From bd8aca004c242d44dbea70c53c81b5bf02c56d67 Mon Sep 17 00:00:00 2001
From: John Hefferman <jhefferman@salesforce.com>
Date: Fri, 12 Sep 2025 13:47:23 -0600
Subject: [PATCH 01/11] feat: added ability to toggle
 experimentalComplexExpressions in ssr fixtures

---
 .../__tests__/fixtures/text-interpolation-complex/.only   | 0
 .../fixtures/text-interpolation-complex/config.json       | 7 +++++++
 .../fixtures/text-interpolation-complex/error.txt         | 0
 .../fixtures/text-interpolation-complex/expected.html     | 6 ++++++
 .../modules/x/text-interpolation/text-interpolation.html  | 3 +++
 .../modules/x/text-interpolation/text-interpolation.js    | 8 ++++++++
 packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts | 7 ++++++-
 7 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/.only
 create mode 100755 packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/config.json
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/error.txt
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected.html
 create mode 100755 packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.html
 create mode 100755 packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.js

diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/.only b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/.only
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/config.json b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/config.json
new file mode 100755
index 0000000000..a2dc92585b
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/config.json
@@ -0,0 +1,7 @@
+{
+    "entry": "x/text-interpolation",
+    "props": {
+        "publicProp": "public-prop"
+    },
+    "experimentalComplexExpressions": true
+}
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/error.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/error.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected.html b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected.html
new file mode 100644
index 0000000000..36620af52d
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected.html
@@ -0,0 +1,6 @@
+<fixture-test>
+  <template shadowrootmode="open">
+    <p>
+    </p>
+  </template>
+</fixture-test>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.html b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.html
new file mode 100755
index 0000000000..852481087d
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.html
@@ -0,0 +1,3 @@
+<template>
+    <p>function call: {privateProp + 1}</p>
+</template>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.js b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.js
new file mode 100755
index 0000000000..0e67491f42
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.js
@@ -0,0 +1,8 @@
+import { LightningElement } from 'lwc';
+
+export default class TextInterpolation extends LightningElement {
+    privateProp = 1;
+    functionCall() {
+        this.privateProp++;
+    }
+}
diff --git a/packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts b/packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts
index 8c39d7ba7c..54d4b5277b 100644
--- a/packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts
+++ b/packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts
@@ -33,6 +33,9 @@ interface FixtureConfig {
 
     /** The string used to uniquely identify one set of dedupe IDs with multiple SSR islands */
     styleDedupe?: string;
+
+    /* TODO [#3370]: remove experimental template expression flag */
+    experimentalComplexExpressions?: boolean;
 }
 
 vi.mock('@lwc/ssr-runtime', async () => {
@@ -51,7 +54,7 @@ vi.mock('@lwc/ssr-runtime', async () => {
 
 const SSR_MODE: CompilationMode = DEFAULT_SSR_MODE;
 
-async function compileFixture({ entry, dirname }: { entry: string; dirname: string }) {
+async function compileFixture({ entry, dirname, experimentalComplexExpressions }: { entry: string; dirname: string, experimentalComplexExpressions: boolean }) {
     const modulesDir = path.resolve(dirname, './modules');
     const outputFile = path.resolve(dirname, './dist/compiled-experimental-ssr.js');
     const input = 'virtual/fixture/test.js';
@@ -73,6 +76,7 @@ async function compileFixture({ entry, dirname }: { entry: string; dirname: stri
                     loader: path.join(__dirname, './utils/custom-loader.js'),
                     strictSpecifier: false,
                 },
+                experimentalComplexExpressions
             }),
         ],
         onwarn({ message, code }) {
@@ -109,6 +113,7 @@ describe.concurrent('fixtures', () => {
                 compiledFixturePath = await compileFixture({
                     entry: config!.entry,
                     dirname,
+                    experimentalComplexExpressions: config!.experimentalComplexExpressions,
                 });
             } catch (err: any) {
                 return {

From 9035b036b81bd878f30b670f0f9c25baad180985 Mon Sep 17 00:00:00 2001
From: John Hefferman <jhefferman@salesforce.com>
Date: Tue, 16 Sep 2025 11:30:21 -0600
Subject: [PATCH 02/11] chore: disable

---
 .../valid/object-expr/.only                   |   0
 .../valid/object-expr/actual.html             |   2 +-
 .../valid/object-expr/ast.json                | 143 ++++--------------
 .../valid/object-expr/expected.js             |  10 +-
 4 files changed, 30 insertions(+), 125 deletions(-)
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/.only

diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/.only b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/.only
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html
index a594536bea..3e2488f2ce 100644
--- a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html
@@ -1,5 +1,5 @@
 <template>
     <section>
-        <x-pert attr="{({ obj: 'literal' })}">{({ obj: 'literal'}).toString()}</x-pert>
+        <x-pert>{foo()}</x-pert>
     </section>
 </template>
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json
index 79af6ab260..b33b77bcc7 100644
--- a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json
@@ -7,7 +7,7 @@
             "endLine": 5,
             "endColumn": 12,
             "start": 0,
-            "end": 139,
+            "end": 84,
             "startTag": {
                 "startLine": 1,
                 "startColumn": 1,
@@ -21,8 +21,8 @@
                 "startColumn": 1,
                 "endLine": 5,
                 "endColumn": 12,
-                "start": 128,
-                "end": 139
+                "start": 73,
+                "end": 84
             }
         },
         "directives": [],
@@ -37,7 +37,7 @@
                     "endLine": 4,
                     "endColumn": 15,
                     "start": 15,
-                    "end": 127,
+                    "end": 72,
                     "startTag": {
                         "startLine": 2,
                         "startColumn": 5,
@@ -51,8 +51,8 @@
                         "startColumn": 5,
                         "endLine": 4,
                         "endColumn": 15,
-                        "start": 117,
-                        "end": 127
+                        "start": 62,
+                        "end": 72
                     }
                 },
                 "attributes": [],
@@ -68,149 +68,62 @@
                             "startLine": 3,
                             "startColumn": 9,
                             "endLine": 3,
-                            "endColumn": 88,
+                            "endColumn": 33,
                             "start": 33,
-                            "end": 112,
+                            "end": 57,
                             "startTag": {
                                 "startLine": 3,
                                 "startColumn": 9,
                                 "endLine": 3,
-                                "endColumn": 47,
+                                "endColumn": 17,
                                 "start": 33,
-                                "end": 71
+                                "end": 41
                             },
                             "endTag": {
                                 "startLine": 3,
-                                "startColumn": 79,
+                                "startColumn": 24,
                                 "endLine": 3,
-                                "endColumn": 88,
-                                "start": 103,
-                                "end": 112
+                                "endColumn": 33,
+                                "start": 48,
+                                "end": 57
                             }
                         },
                         "attributes": [],
-                        "properties": [
-                            {
-                                "type": "Property",
-                                "name": "attr",
-                                "attributeName": "attr",
-                                "value": {
-                                    "type": "ObjectExpression",
-                                    "start": 2,
-                                    "end": 20,
-                                    "properties": [
-                                        {
-                                            "type": "Property",
-                                            "start": 4,
-                                            "end": 18,
-                                            "method": false,
-                                            "shorthand": false,
-                                            "computed": false,
-                                            "key": {
-                                                "type": "Identifier",
-                                                "start": 4,
-                                                "end": 7,
-                                                "name": "obj"
-                                            },
-                                            "value": {
-                                                "type": "Literal",
-                                                "start": 9,
-                                                "end": 18,
-                                                "value": "literal",
-                                                "raw": "'literal'"
-                                            },
-                                            "kind": "init"
-                                        }
-                                    ],
-                                    "location": {
-                                        "startLine": 3,
-                                        "startColumn": 17,
-                                        "endLine": 3,
-                                        "endColumn": 46,
-                                        "start": 41,
-                                        "end": 70
-                                    }
-                                },
-                                "location": {
-                                    "startLine": 3,
-                                    "startColumn": 17,
-                                    "endLine": 3,
-                                    "endColumn": 46,
-                                    "start": 41,
-                                    "end": 70
-                                }
-                            }
-                        ],
+                        "properties": [],
                         "directives": [],
                         "listeners": [],
                         "children": [
                             {
                                 "type": "Text",
-                                "raw": "{({ obj: 'literal'}).toString()}",
+                                "raw": "{foo()}",
                                 "value": {
                                     "type": "CallExpression",
                                     "start": 1,
-                                    "end": 31,
+                                    "end": 6,
                                     "callee": {
-                                        "type": "MemberExpression",
+                                        "type": "Identifier",
                                         "start": 1,
-                                        "end": 29,
-                                        "object": {
-                                            "type": "ObjectExpression",
-                                            "start": 2,
-                                            "end": 19,
-                                            "properties": [
-                                                {
-                                                    "type": "Property",
-                                                    "start": 4,
-                                                    "end": 18,
-                                                    "method": false,
-                                                    "shorthand": false,
-                                                    "computed": false,
-                                                    "key": {
-                                                        "type": "Identifier",
-                                                        "start": 4,
-                                                        "end": 7,
-                                                        "name": "obj"
-                                                    },
-                                                    "value": {
-                                                        "type": "Literal",
-                                                        "start": 9,
-                                                        "end": 18,
-                                                        "value": "literal",
-                                                        "raw": "'literal'"
-                                                    },
-                                                    "kind": "init"
-                                                }
-                                            ]
-                                        },
-                                        "property": {
-                                            "type": "Identifier",
-                                            "start": 21,
-                                            "end": 29,
-                                            "name": "toString"
-                                        },
-                                        "computed": false,
-                                        "optional": false
+                                        "end": 4,
+                                        "name": "foo"
                                     },
                                     "arguments": [],
                                     "optional": false,
                                     "location": {
                                         "startLine": 3,
-                                        "startColumn": 47,
+                                        "startColumn": 17,
                                         "endLine": 3,
-                                        "endColumn": 79,
-                                        "start": 71,
-                                        "end": 103
+                                        "endColumn": 24,
+                                        "start": 41,
+                                        "end": 48
                                     }
                                 },
                                 "location": {
                                     "startLine": 3,
-                                    "startColumn": 47,
+                                    "startColumn": 17,
                                     "endLine": 3,
-                                    "endColumn": 79,
-                                    "start": 71,
-                                    "end": 103
+                                    "endColumn": 24,
+                                    "start": 41,
+                                    "end": 48
                                 }
                             }
                         ]
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js
index 322fe089a7..43dab3dd70 100644
--- a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js
@@ -6,16 +6,8 @@ const stc0 = {
   key: 0,
 };
 const stc1 = {
-  props: {
-    attr: {
-      obj: "literal",
-    },
-  },
   key: 1,
 };
-const stc2 = {
-  obj: "literal",
-};
 function tmpl($api, $cmp, $slotset, $ctx) {
   const {
     d: api_dynamic_text,
@@ -26,7 +18,7 @@ function tmpl($api, $cmp, $slotset, $ctx) {
   return [
     api_element("section", stc0, [
       api_custom_element("x-pert", _xPert, stc1, [
-        api_text(api_dynamic_text(stc2.toString())),
+        api_text(api_dynamic_text($cmp.foo())),
       ]),
     ]),
   ];

From eb7a327d57a0e9daba90bd24a933d86f0e2562a8 Mon Sep 17 00:00:00 2001
From: John Hefferman <jhefferman@salesforce.com>
Date: Wed, 24 Sep 2025 12:33:23 -0600
Subject: [PATCH 03/11] feat: ssr cte support

---
 .../fixtures/text-interpolation-complex/.only |  0
 .../text-interpolation-complex/config.json    |  6 +-
 .../text-interpolation-complex/error.txt      |  1 +
 .../text-interpolation-complex/expected.html  |  6 --
 .../text-interpolation.html                   |  2 +-
 .../text-interpolation/text-interpolation.js  |  8 +-
 .../src/__tests__/fixtures.spec.ts            | 12 ++-
 .../src/compile-template/expression.ts        | 82 ++++++++++++-------
 .../src/compile-template/shared.ts            | 55 -------------
 .../compile-template/transformers/element.ts  |  9 +-
 .../compile-template/transformers/for-each.ts |  7 +-
 .../src/compile-template/transformers/slot.ts | 11 +--
 .../valid/object-expr/.only                   |  0
 .../template-compiler/src/codegen/codegen.ts  | 54 ++----------
 .../src/codegen/expression.ts                 | 74 +++++++++++++++--
 packages/@lwc/template-compiler/src/index.ts  |  1 +
 16 files changed, 163 insertions(+), 165 deletions(-)
 delete mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/.only
 delete mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/.only

diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/.only b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/.only
deleted file mode 100644
index e69de29bb2..0000000000
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/config.json b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/config.json
index a2dc92585b..154db9aa40 100755
--- a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/config.json
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/config.json
@@ -3,5 +3,9 @@
     "props": {
         "publicProp": "public-prop"
     },
-    "experimentalComplexExpressions": true
+    "experimentalComplexExpressions": true,
+    "ssrFiles": {
+        "expected": "expected-ssr.txt",
+        "error": "error-ssr.txt"
+    }
 }
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/error.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/error.txt
index e69de29bb2..35dac9946c 100644
--- a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/error.txt
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/error.txt
@@ -0,0 +1 @@
+LWC1060: Template expression doesn't allow BinaryExpression
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected.html b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected.html
index 36620af52d..e69de29bb2 100644
--- a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected.html
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected.html
@@ -1,6 +0,0 @@
-<fixture-test>
-  <template shadowrootmode="open">
-    <p>
-    </p>
-  </template>
-</fixture-test>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.html b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.html
index 852481087d..2398b50a3d 100755
--- a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.html
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.html
@@ -1,3 +1,3 @@
 <template>
-    <p>function call: {privateProp + 1}</p>
+    <p>{bar() + ' ' + foo()} {foo() + ' ' + bar()}</p>
 </template>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.js b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.js
index 0e67491f42..5959b04818 100755
--- a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.js
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/modules/x/text-interpolation/text-interpolation.js
@@ -1,8 +1,10 @@
 import { LightningElement } from 'lwc';
 
 export default class TextInterpolation extends LightningElement {
-    privateProp = 1;
-    functionCall() {
-        this.privateProp++;
+    foo() {
+        return 'bar';
+    }
+    bar() {
+        return 'foo';
     }
 }
diff --git a/packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts b/packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts
index 54d4b5277b..0af9fa2537 100644
--- a/packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts
+++ b/packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts
@@ -54,7 +54,15 @@ vi.mock('@lwc/ssr-runtime', async () => {
 
 const SSR_MODE: CompilationMode = DEFAULT_SSR_MODE;
 
-async function compileFixture({ entry, dirname, experimentalComplexExpressions }: { entry: string; dirname: string, experimentalComplexExpressions: boolean }) {
+async function compileFixture({
+    entry,
+    dirname,
+    experimentalComplexExpressions,
+}: {
+    entry: string;
+    dirname: string;
+    experimentalComplexExpressions: boolean;
+}) {
     const modulesDir = path.resolve(dirname, './modules');
     const outputFile = path.resolve(dirname, './dist/compiled-experimental-ssr.js');
     const input = 'virtual/fixture/test.js';
@@ -76,7 +84,7 @@ async function compileFixture({ entry, dirname, experimentalComplexExpressions }
                     loader: path.join(__dirname, './utils/custom-loader.js'),
                     strictSpecifier: false,
                 },
-                experimentalComplexExpressions
+                experimentalComplexExpressions,
             }),
         ],
         onwarn({ message, code }) {
diff --git a/packages/@lwc/ssr-compiler/src/compile-template/expression.ts b/packages/@lwc/ssr-compiler/src/compile-template/expression.ts
index 63a3516a05..f554571f12 100644
--- a/packages/@lwc/ssr-compiler/src/compile-template/expression.ts
+++ b/packages/@lwc/ssr-compiler/src/compile-template/expression.ts
@@ -4,45 +4,71 @@
  * SPDX-License-Identifier: MIT
  * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
  */
-
-import { builders as b } from 'estree-toolkit';
-
+import { bindExpression } from '@lwc/template-compiler';
 import type {
     ComplexExpression as IrComplexExpression,
     Expression as IrExpression,
     Identifier as IrIdentifier,
     MemberExpression as IrMemberExpression,
 } from '@lwc/template-compiler';
-import type {
-    Identifier as EsIdentifier,
-    Expression as EsExpression,
-    MemberExpression as EsMemberExpression,
-} from 'estree';
+import type { Identifier as EsIdentifier, Expression as EsExpression } from 'estree';
 import type { TransformerContext } from './types';
 
-function getRootMemberExpression(node: IrMemberExpression): IrMemberExpression {
-    return node.object.type === 'MemberExpression' ? getRootMemberExpression(node.object) : node;
-}
-
 export function expressionIrToEs(
     node: IrExpression | IrComplexExpression,
     cxt: TransformerContext
 ): EsExpression {
-    if (node.type === 'Identifier') {
-        const isLocalVar = cxt.isLocalVar((node as IrIdentifier).name);
-        return isLocalVar
-            ? (node as EsIdentifier)
-            : b.memberExpression(b.identifier('instance'), node as EsIdentifier);
-    } else if (node.type === 'MemberExpression') {
-        const nodeClone = structuredClone(node);
-        const rootMemberExpr = getRootMemberExpression(nodeClone as IrMemberExpression);
-        if (!cxt.isLocalVar((rootMemberExpr.object as IrIdentifier).name)) {
-            rootMemberExpr.object = b.memberExpression(
-                b.identifier('instance'),
-                rootMemberExpr.object as EsIdentifier
-            ) as unknown as IrMemberExpression;
-        }
-        return nodeClone as unknown as EsMemberExpression;
+    return bindExpression(
+        node as IrComplexExpression,
+        (n: EsIdentifier) => cxt.isLocalVar((n as EsIdentifier).name),
+        'instance',
+        cxt.templateOptions.experimentalComplexExpressions
+    );
+}
+
+/**
+ * Given an expression in a context, return an expression that may be scoped to that context.
+ * For example, for the expression `foo`, it will typically be `instance.foo`, but if we're
+ * inside a `for:each` block then the `foo` variable may refer to the scoped `foo`,
+ * e.g. `<template for:each={foos} for:item="foo">`
+ * @param expression
+ * @param cxt
+ */
+export function getScopedExpression(
+    expression: IrExpression,
+    cxt: TransformerContext
+): EsExpression {
+    let scopeReferencedId: IrExpression | null = null;
+    if (expression.type === 'MemberExpression') {
+        // e.g. `foo.bar` -> scopeReferencedId is `foo`
+        scopeReferencedId = getRootIdentifier(expression);
+    } else if (expression.type === 'Identifier') {
+        // e.g. `foo` -> scopeReferencedId is `foo`
+        scopeReferencedId = expression;
     }
-    throw new Error(`Unimplemented expression: ${node.type}`);
+
+    if (scopeReferencedId === null && !cxt.templateOptions.experimentalComplexExpressions) {
+        throw new Error(
+            `Invalid expression, must be a MemberExpression or Identifier, found type="${expression.type}": \`${JSON.stringify(expression)}\``
+        );
+    }
+
+    return cxt.isLocalVar(scopeReferencedId?.name)
+        ? (expression as EsExpression)
+        : expressionIrToEs(expression, cxt);
+}
+
+function getRootMemberExpression(node: IrMemberExpression): IrMemberExpression {
+    return node.object.type === 'MemberExpression' ? getRootMemberExpression(node.object) : node;
+}
+
+function getRootIdentifier(node: IrMemberExpression): IrIdentifier {
+    const rootMemberExpression = getRootMemberExpression(node);
+    if (rootMemberExpression.object.type === 'Identifier') {
+        return rootMemberExpression.object;
+    }
+
+    throw new Error(
+        `Invalid expression, must be an Identifier, found type="${rootMemberExpression.type}": \`${JSON.stringify(rootMemberExpression)}\``
+    );
 }
diff --git a/packages/@lwc/ssr-compiler/src/compile-template/shared.ts b/packages/@lwc/ssr-compiler/src/compile-template/shared.ts
index 2e2e4590a2..33f37c5a8c 100644
--- a/packages/@lwc/ssr-compiler/src/compile-template/shared.ts
+++ b/packages/@lwc/ssr-compiler/src/compile-template/shared.ts
@@ -22,8 +22,6 @@ import type {
 } from '@lwc/template-compiler';
 import type {
     Expression as EsExpression,
-    Identifier as EsIdentifier,
-    MemberExpression as EsMemberExpression,
     ObjectExpression as EsObjectExpression,
     Property as EsProperty,
     Statement as EsStatement,
@@ -79,59 +77,6 @@ export function bAttributeValue(node: IrNode, attrName: string): EsExpression {
     }
 }
 
-function getRootMemberExpression(node: EsMemberExpression): EsMemberExpression {
-    return node.object.type === 'MemberExpression' ? getRootMemberExpression(node.object) : node;
-}
-
-function getRootIdentifier(node: EsMemberExpression, cxt: TransformerContext): EsIdentifier | null {
-    const rootMemberExpression = getRootMemberExpression(node);
-    if (is.identifier(rootMemberExpression.object)) {
-        return rootMemberExpression.object;
-    }
-    if (cxt.templateOptions.experimentalComplexExpressions) {
-        // TODO [#3370]: Implement complex template expressions
-        return null;
-    }
-    // Should be impossible to hit, at least until we implement complex template expressions
-    /* v8 ignore next */
-    throw new Error(
-        `Invalid expression, must be an Identifier, found type="${rootMemberExpression.type}": \`${JSON.stringify(rootMemberExpression)}\``
-    );
-}
-
-/**
- * Given an expression in a context, return an expression that may be scoped to that context.
- * For example, for the expression `foo`, it will typically be `instance.foo`, but if we're
- * inside a `for:each` block then the `foo` variable may refer to the scoped `foo`,
- * e.g. `<template for:each={foos} for:item="foo">`
- * @param expression
- * @param cxt
- */
-export function getScopedExpression(expression: EsExpression, cxt: TransformerContext) {
-    let scopeReferencedId: EsExpression | null = null;
-    if (is.memberExpression(expression)) {
-        // e.g. `foo.bar` -> scopeReferencedId is `foo`
-        scopeReferencedId = getRootIdentifier(expression, cxt);
-    } else if (is.identifier(expression)) {
-        // e.g. `foo` -> scopeReferencedId is `foo`
-        scopeReferencedId = expression;
-    }
-    if (scopeReferencedId === null) {
-        if (cxt.templateOptions.experimentalComplexExpressions) {
-            // TODO [#3370]: Implement complex template expressions
-            return expression;
-        }
-        // Should be impossible to hit, at least until we implement complex template expressions
-        /* v8 ignore next */
-        throw new Error(
-            `Invalid expression, must be a MemberExpression or Identifier, found type="${expression.type}": \`${JSON.stringify(expression)}\``
-        );
-    }
-    return cxt.isLocalVar(scopeReferencedId.name)
-        ? expression
-        : b.memberExpression(b.identifier('instance'), expression);
-}
-
 export function normalizeClassAttributeValue(value: string) {
     // @ts-expect-error weird indirection results in wrong overload being picked up
     return StringReplace.call(StringTrim.call(value), /\s+/g, ' ');
diff --git a/packages/@lwc/ssr-compiler/src/compile-template/transformers/element.ts b/packages/@lwc/ssr-compiler/src/compile-template/transformers/element.ts
index 32c673fe7c..a6646d0a36 100644
--- a/packages/@lwc/ssr-compiler/src/compile-template/transformers/element.ts
+++ b/packages/@lwc/ssr-compiler/src/compile-template/transformers/element.ts
@@ -20,16 +20,15 @@ import {
     type Property as IrProperty,
 } from '@lwc/template-compiler';
 import { esTemplateWithYield } from '../../estemplate';
-import { expressionIrToEs } from '../expression';
+import { expressionIrToEs, getScopedExpression } from '../expression';
 import { irChildrenToEs } from '../ir-to-es';
-import { getScopedExpression, normalizeClassAttributeValue } from '../shared';
+import { normalizeClassAttributeValue } from '../shared';
 import type {
     ExternalComponent as IrExternalComponent,
     Slot as IrSlot,
 } from '@lwc/template-compiler';
 
 import type {
-    BinaryExpression,
     BlockStatement as EsBlockStatement,
     Expression as EsExpression,
     Statement as EsStatement,
@@ -165,11 +164,11 @@ function yieldAttrOrPropLiteralValue(name: string, valueNode: IrLiteral): EsStat
 function yieldAttrOrPropDynamicValue(
     elementName: string,
     name: string,
-    value: IrExpression | BinaryExpression,
+    value: IrExpression,
     cxt: TransformerContext
 ): EsStatement[] {
     cxt.import('htmlEscape');
-    const scopedExpression = getScopedExpression(value as EsExpression, cxt);
+    const scopedExpression = getScopedExpression(value, cxt);
     switch (name) {
         case 'class':
             cxt.import('normalizeClass');
diff --git a/packages/@lwc/ssr-compiler/src/compile-template/transformers/for-each.ts b/packages/@lwc/ssr-compiler/src/compile-template/transformers/for-each.ts
index a4b3d53e2a..be53b0b2d2 100644
--- a/packages/@lwc/ssr-compiler/src/compile-template/transformers/for-each.ts
+++ b/packages/@lwc/ssr-compiler/src/compile-template/transformers/for-each.ts
@@ -8,10 +8,11 @@
 import { builders as b, is } from 'estree-toolkit';
 import { esTemplate } from '../../estemplate';
 import { irChildrenToEs } from '../ir-to-es';
-import { getScopedExpression, optimizeAdjacentYieldStmts } from '../shared';
+import { optimizeAdjacentYieldStmts } from '../shared';
 
+import { getScopedExpression } from '../expression';
 import type { ForEach as IrForEach } from '@lwc/template-compiler';
-import type { Expression as EsExpression, ForOfStatement as EsForOfStatement } from 'estree';
+import type { ForOfStatement as EsForOfStatement } from 'estree';
 import type { Transformer } from '../types';
 
 const bForOfYieldFrom = esTemplate`
@@ -28,7 +29,7 @@ export const ForEach: Transformer<IrForEach> = function ForEach(node, cxt): EsFo
     const forEachStatements = irChildrenToEs(node.children, cxt);
     cxt.popLocalVars();
 
-    const expression = node.expression as EsExpression;
+    const expression = node.expression;
     const iterable = getScopedExpression(expression, cxt);
 
     return [
diff --git a/packages/@lwc/ssr-compiler/src/compile-template/transformers/slot.ts b/packages/@lwc/ssr-compiler/src/compile-template/transformers/slot.ts
index 60aa64a91c..ff8210166f 100644
--- a/packages/@lwc/ssr-compiler/src/compile-template/transformers/slot.ts
+++ b/packages/@lwc/ssr-compiler/src/compile-template/transformers/slot.ts
@@ -10,15 +10,12 @@ import { is, builders as b } from 'estree-toolkit';
 import { esTemplateWithYield } from '../../estemplate';
 
 import { irChildrenToEs } from '../ir-to-es';
-import { bAttributeValue, getScopedExpression } from '../shared';
+import { bAttributeValue } from '../shared';
 import { isNullableOf } from '../../estree/validators';
+import { getScopedExpression } from '../expression';
 import { Element } from './element';
 import type { Slot as IrSlot } from '@lwc/template-compiler';
-import type {
-    Statement as EsStatement,
-    IfStatement as EsIfStatement,
-    Expression as EsExpression,
-} from 'estree';
+import type { Statement as EsStatement, IfStatement as EsIfStatement } from 'estree';
 import type { Transformer } from '../types';
 
 const bConditionalSlot = esTemplateWithYield`
@@ -86,7 +83,7 @@ const bConditionalSlot = esTemplateWithYield`
 export const Slot: Transformer<IrSlot> = function Slot(node, ctx): EsStatement[] {
     const slotBindDirective = node.directives.find((dir) => dir.name === 'SlotBind');
     const slotBound = slotBindDirective?.value
-        ? getScopedExpression(slotBindDirective.value as EsExpression, ctx)
+        ? getScopedExpression(slotBindDirective.value, ctx)
         : null;
     const slotName = bAttributeValue(node, 'name');
     // FIXME: avoid serializing the slot's children twice
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/.only b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/.only
deleted file mode 100644
index e69de29bb2..0000000000
diff --git a/packages/@lwc/template-compiler/src/codegen/codegen.ts b/packages/@lwc/template-compiler/src/codegen/codegen.ts
index b991b09104..e1da655d4c 100644
--- a/packages/@lwc/template-compiler/src/codegen/codegen.ts
+++ b/packages/@lwc/template-compiler/src/codegen/codegen.ts
@@ -4,7 +4,6 @@
  * SPDX-License-Identifier: MIT
  * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
  */
-import { walk } from 'estree-walker';
 import {
     getAPIVersionFromNumber,
     SVG_NAMESPACE,
@@ -47,7 +46,7 @@ import {
     hasDynamicText,
 } from './static-element';
 import { serializeStaticElement } from './static-element-serializer';
-import { bindAttributeExpression, bindComplexExpression } from './expression';
+import { bindAttributeExpression, bindExpression } from './expression';
 import type State from '../state';
 import type {
     ChildNode,
@@ -65,7 +64,6 @@ import type {
     OnDirective,
 } from '../shared/types';
 import type { APIVersion } from '@lwc/shared';
-import type { Node } from 'estree-walker';
 
 type RenderPrimitive =
     | 'iterator'
@@ -630,50 +628,12 @@ export default class CodeGen {
      * @param expression
      */
     bindExpression(expression: Expression | Literal | ComplexExpression): t.Expression {
-        if (t.isIdentifier(expression)) {
-            if (!this.isLocalIdentifier(expression)) {
-                return t.memberExpression(t.identifier(TEMPLATE_PARAMS.INSTANCE), expression);
-            } else {
-                return expression;
-            }
-        }
-
-        // TODO [#3370]: remove experimental template expression flag
-        if (this.state.config.experimentalComplexExpressions) {
-            // Cloning here is necessary because `this.replace()` is destructive, and we might use the
-            // node later during static content optimization
-            expression = structuredClone(expression);
-            return bindComplexExpression(expression as ComplexExpression, this);
-        }
-
-        // We need access to both this `this` and the walker's `this` in the walker
-        // eslint-disable-next-line @typescript-eslint/no-this-alias
-        const scope = this;
-
-        // Cloning here is necessary because `this.replace()` is destructive, and we might use the
-        // node later during static content optimization
-        expression = structuredClone(expression);
-        // TODO [#3370]: when the template expression flag is removed, the
-        // ComplexExpression type should be redefined as an ESTree Node. Doing
-        // so when the flag is still in place results in a cascade of required
-        // type changes across the codebase.
-        walk(expression as Node, {
-            leave(node, parent) {
-                if (
-                    parent !== null &&
-                    t.isIdentifier(node) &&
-                    t.isMemberExpression(parent) &&
-                    parent.object === node &&
-                    !scope.isLocalIdentifier(node)
-                ) {
-                    this.replace(
-                        t.memberExpression(t.identifier(TEMPLATE_PARAMS.INSTANCE), node) as Node
-                    );
-                }
-            },
-        });
-
-        return expression as t.Expression;
+        return bindExpression(
+            expression,
+            this.isLocalIdentifier.bind(this),
+            TEMPLATE_PARAMS.INSTANCE,
+            this.state.config.experimentalComplexExpressions
+        );
     }
 
     genStaticElement(element: StaticElement, slotParentName?: string): t.Expression {
diff --git a/packages/@lwc/template-compiler/src/codegen/expression.ts b/packages/@lwc/template-compiler/src/codegen/expression.ts
index e0ceccc1fa..cc17a3f6aa 100644
--- a/packages/@lwc/template-compiler/src/codegen/expression.ts
+++ b/packages/@lwc/template-compiler/src/codegen/expression.ts
@@ -9,7 +9,6 @@ import { walk } from 'estree-walker';
 import { ParserDiagnostics, invariant } from '@lwc/errors';
 import { isBooleanAttribute } from '@lwc/shared';
 import * as t from '../shared/estree';
-import { TEMPLATE_PARAMS } from '../shared/constants';
 import { isProperty, isStringLiteral } from '../shared/ast';
 import {
     isAllowedFragOnlyUrlsXHTML,
@@ -18,7 +17,13 @@ import {
     isIdReferencingAttribute,
     isSvgUseHref,
 } from '../parser/attribute';
-import type { Attribute, BaseElement, ComplexExpression, Property } from '../shared/types';
+import type {
+    Attribute,
+    BaseElement,
+    Expression,
+    ComplexExpression,
+    Property,
+} from '../shared/types';
 import type { Node } from 'estree-walker';
 import type CodeGen from './codegen';
 
@@ -26,6 +31,62 @@ type VariableName = string;
 type VariableShadowingMultiplicity = number;
 type VariableNames = Set<string>;
 
+/**
+ * Bind the passed expression to the component instance. It applies the following transformation to the expression:
+ * - {value} --> {$cmp.value}
+ * - {value[index]} --> {$cmp.value[$cmp.index]}
+ * @param expression
+ */
+export function bindExpression(
+    expression: Expression | t.Literal | ComplexExpression,
+    isLocalIdentifier: (node: t.Identifier) => boolean,
+    templateInstanceName: string,
+    experimentalComplexExpressions: boolean
+): t.Expression {
+    if (t.isIdentifier(expression)) {
+        if (!isLocalIdentifier(expression)) {
+            return t.memberExpression(t.identifier(templateInstanceName), expression);
+        } else {
+            return expression;
+        }
+    }
+
+    // TODO [#3370]: remove experimental template expression flag
+    if (experimentalComplexExpressions) {
+        // Cloning here is necessary because `this.replace()` is destructive, and we might use the
+        // node later during static content optimization
+        expression = structuredClone(expression);
+        return bindComplexExpression(
+            expression as ComplexExpression,
+            isLocalIdentifier,
+            templateInstanceName
+        );
+    }
+
+    // Cloning here is necessary because `this.replace()` is destructive, and we might use the
+    // node later during static content optimization
+    expression = structuredClone(expression);
+    // TODO [#3370]: when the template expression flag is removed, the
+    // ComplexExpression type should be redefined as an ESTree Node. Doing
+    // so when the flag is still in place results in a cascade of required
+    // type changes across the codebase.
+    walk(expression as Node, {
+        leave(node, parent) {
+            if (
+                parent !== null &&
+                t.isIdentifier(node) &&
+                t.isMemberExpression(parent) &&
+                parent.object === node &&
+                !isLocalIdentifier(node)
+            ) {
+                this.replace(t.memberExpression(t.identifier(templateInstanceName), node) as Node);
+            }
+        },
+    });
+
+    return expression as t.Expression;
+}
+
 /**
  * Bind the passed expression to the component instance. It applies the following
  * transformation to the expression:
@@ -49,7 +110,8 @@ type VariableNames = Set<string>;
  */
 export function bindComplexExpression(
     expression: ComplexExpression,
-    codeGen: CodeGen
+    isLocalIdentifier: (node: t.Identifier) => boolean,
+    templateInstanceName: string
 ): t.Expression {
     const expressionScopes = new ExpressionScopes();
     // TODO [#3370]: when the template expression flag is removed, the
@@ -76,12 +138,10 @@ export function bindComplexExpression(
                 isIdentifier &&
                 !(t.isMemberExpression(parent) && parent.property === node && !parent.computed) &&
                 !(t.isProperty(parent) && parent.key === node) &&
-                !codeGen.isLocalIdentifier(node) &&
+                !isLocalIdentifier(node) &&
                 !expressionScopes.isScopedToExpression(node)
             ) {
-                this.replace(
-                    t.memberExpression(t.identifier(TEMPLATE_PARAMS.INSTANCE), node) as Node
-                );
+                this.replace(t.memberExpression(t.identifier(templateInstanceName), node) as Node);
             }
         },
     });
diff --git a/packages/@lwc/template-compiler/src/index.ts b/packages/@lwc/template-compiler/src/index.ts
index f16cfe1aab..5cd5f37b98 100644
--- a/packages/@lwc/template-compiler/src/index.ts
+++ b/packages/@lwc/template-compiler/src/index.ts
@@ -22,6 +22,7 @@ export { Config } from './config';
 export { toPropertyName } from './shared/utils';
 export { kebabcaseToCamelcase } from './shared/naming';
 export { generateScopeTokens } from './scopeTokens';
+export { bindExpression } from './codegen/expression';
 
 /**
  * Parses HTML markup into an AST

From 59e2002eff1cbd567479175612525a46b8b90d0a Mon Sep 17 00:00:00 2001
From: John Hefferman <jhefferman@salesforce.com>
Date: Wed, 24 Sep 2025 12:35:40 -0600
Subject: [PATCH 04/11] fix: ssr coverage

---
 .../fixtures/attribute-dynamic-complex/config.json     |  8 ++++++++
 .../fixtures/attribute-dynamic-complex/error-ssr.txt   |  0
 .../fixtures/attribute-dynamic-complex/error.txt       |  1 +
 .../attribute-dynamic-complex/expected-ssr.txt         |  6 ++++++
 .../fixtures/attribute-dynamic-complex/expected.html   |  0
 .../attribute-dynamic-complex.html                     |  3 +++
 .../attribute-dynamic-complex.js                       | 10 ++++++++++
 .../fixtures/text-interpolation-complex/error-ssr.txt  |  0
 .../text-interpolation-complex/expected-ssr.txt        |  7 +++++++
 9 files changed, 35 insertions(+)
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/config.json
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/error-ssr.txt
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/error.txt
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected-ssr.txt
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected.html
 create mode 100755 packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/modules/x/attribute-dynamic-complex/attribute-dynamic-complex.html
 create mode 100755 packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/modules/x/attribute-dynamic-complex/attribute-dynamic-complex.js
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/error-ssr.txt
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected-ssr.txt

diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/config.json b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/config.json
new file mode 100644
index 0000000000..90324f894b
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/config.json
@@ -0,0 +1,8 @@
+{
+    "entry": "x/attribute-dynamic-complex",
+    "experimentalComplexExpressions": true,
+    "ssrFiles": {
+        "expected": "expected-ssr.txt",
+        "error": "error-ssr.txt"
+    }
+}
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/error-ssr.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/error-ssr.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/error.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/error.txt
new file mode 100644
index 0000000000..b7603fab66
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/error.txt
@@ -0,0 +1 @@
+LWC1034: Ambiguous attribute value class="{bar() + foo()}". If you want to make it a valid identifier you should remove the surrounding quotes class={bar() + foo()}. If you want to make it a string you should escape it class="\{bar() + foo()}".
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected-ssr.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected-ssr.txt
new file mode 100644
index 0000000000..259866046b
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected-ssr.txt
@@ -0,0 +1,6 @@
+<fixture-test>
+  <template shadowrootmode="open">
+    <div class="foobar">
+    </div>
+  </template>
+</fixture-test>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected.html b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected.html
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/modules/x/attribute-dynamic-complex/attribute-dynamic-complex.html b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/modules/x/attribute-dynamic-complex/attribute-dynamic-complex.html
new file mode 100755
index 0000000000..4f9c66db53
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/modules/x/attribute-dynamic-complex/attribute-dynamic-complex.html
@@ -0,0 +1,3 @@
+<template>
+    <div class="{bar() + foo()}"></div>
+</template>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/modules/x/attribute-dynamic-complex/attribute-dynamic-complex.js b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/modules/x/attribute-dynamic-complex/attribute-dynamic-complex.js
new file mode 100755
index 0000000000..602273dffa
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/modules/x/attribute-dynamic-complex/attribute-dynamic-complex.js
@@ -0,0 +1,10 @@
+import { LightningElement } from 'lwc';
+
+export default class AttributeDynamicComplex extends LightningElement {
+    bar() {
+        return 'foo';
+    }
+    foo() {
+        return 'bar';
+    }
+}
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/error-ssr.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/error-ssr.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected-ssr.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected-ssr.txt
new file mode 100644
index 0000000000..68f5d530f9
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected-ssr.txt
@@ -0,0 +1,7 @@
+<fixture-test>
+  <template shadowrootmode="open">
+    <p>
+      foo bar bar foo
+    </p>
+  </template>
+</fixture-test>
\ No newline at end of file

From db0723786fd699228f45ef75d57f32bd5d6066a5 Mon Sep 17 00:00:00 2001
From: John Hefferman <jhefferman@salesforce.com>
Date: Wed, 24 Sep 2025 12:39:05 -0600
Subject: [PATCH 05/11] chore: revert test change

---
 .../valid/object-expr/actual.html             |   2 +-
 .../valid/object-expr/ast.json                | 143 ++++++++++++++----
 .../valid/object-expr/expected.js             |  10 +-
 3 files changed, 125 insertions(+), 30 deletions(-)

diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html
index 3e2488f2ce..a594536bea 100644
--- a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html
@@ -1,5 +1,5 @@
 <template>
     <section>
-        <x-pert>{foo()}</x-pert>
+        <x-pert attr="{({ obj: 'literal' })}">{({ obj: 'literal'}).toString()}</x-pert>
     </section>
 </template>
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json
index b33b77bcc7..79af6ab260 100644
--- a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json
@@ -7,7 +7,7 @@
             "endLine": 5,
             "endColumn": 12,
             "start": 0,
-            "end": 84,
+            "end": 139,
             "startTag": {
                 "startLine": 1,
                 "startColumn": 1,
@@ -21,8 +21,8 @@
                 "startColumn": 1,
                 "endLine": 5,
                 "endColumn": 12,
-                "start": 73,
-                "end": 84
+                "start": 128,
+                "end": 139
             }
         },
         "directives": [],
@@ -37,7 +37,7 @@
                     "endLine": 4,
                     "endColumn": 15,
                     "start": 15,
-                    "end": 72,
+                    "end": 127,
                     "startTag": {
                         "startLine": 2,
                         "startColumn": 5,
@@ -51,8 +51,8 @@
                         "startColumn": 5,
                         "endLine": 4,
                         "endColumn": 15,
-                        "start": 62,
-                        "end": 72
+                        "start": 117,
+                        "end": 127
                     }
                 },
                 "attributes": [],
@@ -68,62 +68,149 @@
                             "startLine": 3,
                             "startColumn": 9,
                             "endLine": 3,
-                            "endColumn": 33,
+                            "endColumn": 88,
                             "start": 33,
-                            "end": 57,
+                            "end": 112,
                             "startTag": {
                                 "startLine": 3,
                                 "startColumn": 9,
                                 "endLine": 3,
-                                "endColumn": 17,
+                                "endColumn": 47,
                                 "start": 33,
-                                "end": 41
+                                "end": 71
                             },
                             "endTag": {
                                 "startLine": 3,
-                                "startColumn": 24,
+                                "startColumn": 79,
                                 "endLine": 3,
-                                "endColumn": 33,
-                                "start": 48,
-                                "end": 57
+                                "endColumn": 88,
+                                "start": 103,
+                                "end": 112
                             }
                         },
                         "attributes": [],
-                        "properties": [],
+                        "properties": [
+                            {
+                                "type": "Property",
+                                "name": "attr",
+                                "attributeName": "attr",
+                                "value": {
+                                    "type": "ObjectExpression",
+                                    "start": 2,
+                                    "end": 20,
+                                    "properties": [
+                                        {
+                                            "type": "Property",
+                                            "start": 4,
+                                            "end": 18,
+                                            "method": false,
+                                            "shorthand": false,
+                                            "computed": false,
+                                            "key": {
+                                                "type": "Identifier",
+                                                "start": 4,
+                                                "end": 7,
+                                                "name": "obj"
+                                            },
+                                            "value": {
+                                                "type": "Literal",
+                                                "start": 9,
+                                                "end": 18,
+                                                "value": "literal",
+                                                "raw": "'literal'"
+                                            },
+                                            "kind": "init"
+                                        }
+                                    ],
+                                    "location": {
+                                        "startLine": 3,
+                                        "startColumn": 17,
+                                        "endLine": 3,
+                                        "endColumn": 46,
+                                        "start": 41,
+                                        "end": 70
+                                    }
+                                },
+                                "location": {
+                                    "startLine": 3,
+                                    "startColumn": 17,
+                                    "endLine": 3,
+                                    "endColumn": 46,
+                                    "start": 41,
+                                    "end": 70
+                                }
+                            }
+                        ],
                         "directives": [],
                         "listeners": [],
                         "children": [
                             {
                                 "type": "Text",
-                                "raw": "{foo()}",
+                                "raw": "{({ obj: 'literal'}).toString()}",
                                 "value": {
                                     "type": "CallExpression",
                                     "start": 1,
-                                    "end": 6,
+                                    "end": 31,
                                     "callee": {
-                                        "type": "Identifier",
+                                        "type": "MemberExpression",
                                         "start": 1,
-                                        "end": 4,
-                                        "name": "foo"
+                                        "end": 29,
+                                        "object": {
+                                            "type": "ObjectExpression",
+                                            "start": 2,
+                                            "end": 19,
+                                            "properties": [
+                                                {
+                                                    "type": "Property",
+                                                    "start": 4,
+                                                    "end": 18,
+                                                    "method": false,
+                                                    "shorthand": false,
+                                                    "computed": false,
+                                                    "key": {
+                                                        "type": "Identifier",
+                                                        "start": 4,
+                                                        "end": 7,
+                                                        "name": "obj"
+                                                    },
+                                                    "value": {
+                                                        "type": "Literal",
+                                                        "start": 9,
+                                                        "end": 18,
+                                                        "value": "literal",
+                                                        "raw": "'literal'"
+                                                    },
+                                                    "kind": "init"
+                                                }
+                                            ]
+                                        },
+                                        "property": {
+                                            "type": "Identifier",
+                                            "start": 21,
+                                            "end": 29,
+                                            "name": "toString"
+                                        },
+                                        "computed": false,
+                                        "optional": false
                                     },
                                     "arguments": [],
                                     "optional": false,
                                     "location": {
                                         "startLine": 3,
-                                        "startColumn": 17,
+                                        "startColumn": 47,
                                         "endLine": 3,
-                                        "endColumn": 24,
-                                        "start": 41,
-                                        "end": 48
+                                        "endColumn": 79,
+                                        "start": 71,
+                                        "end": 103
                                     }
                                 },
                                 "location": {
                                     "startLine": 3,
-                                    "startColumn": 17,
+                                    "startColumn": 47,
                                     "endLine": 3,
-                                    "endColumn": 24,
-                                    "start": 41,
-                                    "end": 48
+                                    "endColumn": 79,
+                                    "start": 71,
+                                    "end": 103
                                 }
                             }
                         ]
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js
index 43dab3dd70..322fe089a7 100644
--- a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js
@@ -6,8 +6,16 @@ const stc0 = {
   key: 0,
 };
 const stc1 = {
+  props: {
+    attr: {
+      obj: "literal",
+    },
+  },
   key: 1,
 };
+const stc2 = {
+  obj: "literal",
+};
 function tmpl($api, $cmp, $slotset, $ctx) {
   const {
     d: api_dynamic_text,
@@ -18,7 +26,7 @@ function tmpl($api, $cmp, $slotset, $ctx) {
   return [
     api_element("section", stc0, [
       api_custom_element("x-pert", _xPert, stc1, [
-        api_text(api_dynamic_text($cmp.foo())),
+        api_text(api_dynamic_text(stc2.toString())),
       ]),
     ]),
   ];

From 3b9d43adba060c88890080d9a87b16840b2e1d00 Mon Sep 17 00:00:00 2001
From: John Hefferman <jhefferman@salesforce.com>
Date: Wed, 24 Sep 2025 14:01:00 -0600
Subject: [PATCH 06/11] fix: additional testing around ssr specific codepaths

---
 .../attribute-dynamic-complex/config.json     |   2 +-
 .../expected-ssr.txt                          |   6 -
 .../text-interpolation-complex/config.json    |   2 +-
 .../expected-ssr.txt                          |   7 -
 .../valid/object-expr/actual.html             |  10 +-
 .../valid/object-expr/ast.json                | 349 ++++++++++--------
 .../valid/object-expr/expected.js             |  39 +-
 7 files changed, 222 insertions(+), 193 deletions(-)
 delete mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected-ssr.txt
 delete mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected-ssr.txt

diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/config.json b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/config.json
index 90324f894b..3af06c8613 100644
--- a/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/config.json
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/config.json
@@ -2,7 +2,7 @@
     "entry": "x/attribute-dynamic-complex",
     "experimentalComplexExpressions": true,
     "ssrFiles": {
-        "expected": "expected-ssr.txt",
+        "expected": "expected-ssr.html",
         "error": "error-ssr.txt"
     }
 }
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected-ssr.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected-ssr.txt
deleted file mode 100644
index 259866046b..0000000000
--- a/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected-ssr.txt
+++ /dev/null
@@ -1,6 +0,0 @@
-<fixture-test>
-  <template shadowrootmode="open">
-    <div class="foobar">
-    </div>
-  </template>
-</fixture-test>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/config.json b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/config.json
index 154db9aa40..7f133355aa 100755
--- a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/config.json
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/config.json
@@ -5,7 +5,7 @@
     },
     "experimentalComplexExpressions": true,
     "ssrFiles": {
-        "expected": "expected-ssr.txt",
+        "expected": "expected-ssr.html",
         "error": "error-ssr.txt"
     }
 }
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected-ssr.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected-ssr.txt
deleted file mode 100644
index 68f5d530f9..0000000000
--- a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected-ssr.txt
+++ /dev/null
@@ -1,7 +0,0 @@
-<fixture-test>
-  <template shadowrootmode="open">
-    <p>
-      foo bar bar foo
-    </p>
-  </template>
-</fixture-test>
\ No newline at end of file
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html
index a594536bea..664b217367 100644
--- a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html
@@ -1,5 +1,7 @@
 <template>
-    <section>
-        <x-pert attr="{({ obj: 'literal' })}">{({ obj: 'literal'}).toString()}</x-pert>
-    </section>
-</template>
+    <ul>
+        <template for:each="{list()}" for:item="item" for:index="index">
+            <li key={item}>{index} - {item}</li>
+        </template>
+    </ul>
+</template>
\ No newline at end of file
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json
index 79af6ab260..52c9d119bb 100644
--- a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json
@@ -4,10 +4,10 @@
         "location": {
             "startLine": 1,
             "startColumn": 1,
-            "endLine": 5,
+            "endLine": 7,
             "endColumn": 12,
             "start": 0,
-            "end": 139,
+            "end": 183,
             "startTag": {
                 "startLine": 1,
                 "startColumn": 1,
@@ -17,42 +17,42 @@
                 "end": 10
             },
             "endTag": {
-                "startLine": 5,
+                "startLine": 7,
                 "startColumn": 1,
-                "endLine": 5,
+                "endLine": 7,
                 "endColumn": 12,
-                "start": 128,
-                "end": 139
+                "start": 172,
+                "end": 183
             }
         },
         "directives": [],
         "children": [
             {
                 "type": "Element",
-                "name": "section",
+                "name": "ul",
                 "namespace": "http://www.w3.org/1999/xhtml",
                 "location": {
                     "startLine": 2,
                     "startColumn": 5,
-                    "endLine": 4,
-                    "endColumn": 15,
+                    "endLine": 6,
+                    "endColumn": 10,
                     "start": 15,
-                    "end": 127,
+                    "end": 171,
                     "startTag": {
                         "startLine": 2,
                         "startColumn": 5,
                         "endLine": 2,
-                        "endColumn": 14,
+                        "endColumn": 9,
                         "start": 15,
-                        "end": 24
+                        "end": 19
                     },
                     "endTag": {
-                        "startLine": 4,
+                        "startLine": 6,
                         "startColumn": 5,
-                        "endLine": 4,
-                        "endColumn": 15,
-                        "start": 117,
-                        "end": 127
+                        "endLine": 6,
+                        "endColumn": 10,
+                        "start": 166,
+                        "end": 171
                     }
                 },
                 "attributes": [],
@@ -61,157 +61,198 @@
                 "listeners": [],
                 "children": [
                     {
-                        "type": "Component",
-                        "name": "x-pert",
-                        "namespace": "http://www.w3.org/1999/xhtml",
-                        "location": {
-                            "startLine": 3,
-                            "startColumn": 9,
-                            "endLine": 3,
-                            "endColumn": 88,
-                            "start": 33,
-                            "end": 112,
-                            "startTag": {
+                        "type": "ForEach",
+                        "expression": {
+                            "type": "CallExpression",
+                            "start": 1,
+                            "end": 7,
+                            "callee": {
+                                "type": "Identifier",
+                                "start": 1,
+                                "end": 5,
+                                "name": "list"
+                            },
+                            "arguments": [],
+                            "optional": false,
+                            "location": {
                                 "startLine": 3,
-                                "startColumn": 9,
+                                "startColumn": 19,
                                 "endLine": 3,
-                                "endColumn": 47,
-                                "start": 33,
-                                "end": 71
-                            },
-                            "endTag": {
+                                "endColumn": 38,
+                                "start": 38,
+                                "end": 57
+                            }
+                        },
+                        "item": {
+                            "type": "Identifier",
+                            "name": "item",
+                            "location": {
                                 "startLine": 3,
-                                "startColumn": 79,
+                                "startColumn": 39,
                                 "endLine": 3,
-                                "endColumn": 88,
-                                "start": 103,
-                                "end": 112
+                                "endColumn": 54,
+                                "start": 58,
+                                "end": 73
                             }
                         },
-                        "attributes": [],
-                        "properties": [
-                            {
-                                "type": "Property",
-                                "name": "attr",
-                                "attributeName": "attr",
-                                "value": {
-                                    "type": "ObjectExpression",
-                                    "start": 2,
-                                    "end": 20,
-                                    "properties": [
-                                        {
-                                            "type": "Property",
-                                            "start": 4,
-                                            "end": 18,
-                                            "method": false,
-                                            "shorthand": false,
-                                            "computed": false,
-                                            "key": {
-                                                "type": "Identifier",
-                                                "start": 4,
-                                                "end": 7,
-                                                "name": "obj"
-                                            },
-                                            "value": {
-                                                "type": "Literal",
-                                                "start": 9,
-                                                "end": 18,
-                                                "value": "literal",
-                                                "raw": "'literal'"
-                                            },
-                                            "kind": "init"
-                                        }
-                                    ],
-                                    "location": {
-                                        "startLine": 3,
-                                        "startColumn": 17,
-                                        "endLine": 3,
-                                        "endColumn": 46,
-                                        "start": 41,
-                                        "end": 70
-                                    }
-                                },
-                                "location": {
-                                    "startLine": 3,
-                                    "startColumn": 17,
-                                    "endLine": 3,
-                                    "endColumn": 46,
-                                    "start": 41,
-                                    "end": 70
-                                }
+                        "index": {
+                            "type": "Identifier",
+                            "name": "index",
+                            "location": {
+                                "startLine": 3,
+                                "startColumn": 55,
+                                "endLine": 3,
+                                "endColumn": 72,
+                                "start": 74,
+                                "end": 91
                             }
-                        ],
-                        "directives": [],
-                        "listeners": [],
+                        },
+                        "location": {
+                            "startLine": 3,
+                            "startColumn": 9,
+                            "endLine": 5,
+                            "endColumn": 20,
+                            "start": 28,
+                            "end": 161
+                        },
+                        "directiveLocation": {
+                            "startLine": 3,
+                            "startColumn": 19,
+                            "endLine": 3,
+                            "endColumn": 38,
+                            "start": 38,
+                            "end": 57
+                        },
                         "children": [
                             {
-                                "type": "Text",
-                                "raw": "{({ obj: 'literal'}).toString()}",
-                                "value": {
-                                    "type": "CallExpression",
-                                    "start": 1,
-                                    "end": 31,
-                                    "callee": {
-                                        "type": "MemberExpression",
-                                        "start": 1,
-                                        "end": 29,
-                                        "object": {
-                                            "type": "ObjectExpression",
-                                            "start": 2,
-                                            "end": 19,
-                                            "properties": [
-                                                {
-                                                    "type": "Property",
-                                                    "start": 4,
-                                                    "end": 18,
-                                                    "method": false,
-                                                    "shorthand": false,
-                                                    "computed": false,
-                                                    "key": {
-                                                        "type": "Identifier",
-                                                        "start": 4,
-                                                        "end": 7,
-                                                        "name": "obj"
-                                                    },
-                                                    "value": {
-                                                        "type": "Literal",
-                                                        "start": 9,
-                                                        "end": 18,
-                                                        "value": "literal",
-                                                        "raw": "'literal'"
-                                                    },
-                                                    "kind": "init"
-                                                }
-                                            ]
+                                "type": "Element",
+                                "name": "li",
+                                "namespace": "http://www.w3.org/1999/xhtml",
+                                "location": {
+                                    "startLine": 4,
+                                    "startColumn": 13,
+                                    "endLine": 4,
+                                    "endColumn": 49,
+                                    "start": 105,
+                                    "end": 141,
+                                    "startTag": {
+                                        "startLine": 4,
+                                        "startColumn": 13,
+                                        "endLine": 4,
+                                        "endColumn": 28,
+                                        "start": 105,
+                                        "end": 120
+                                    },
+                                    "endTag": {
+                                        "startLine": 4,
+                                        "startColumn": 44,
+                                        "endLine": 4,
+                                        "endColumn": 49,
+                                        "start": 136,
+                                        "end": 141
+                                    }
+                                },
+                                "attributes": [],
+                                "properties": [],
+                                "directives": [
+                                    {
+                                        "type": "Directive",
+                                        "name": "Key",
+                                        "value": {
+                                            "type": "Identifier",
+                                            "start": 1,
+                                            "end": 5,
+                                            "name": "item",
+                                            "location": {
+                                                "startLine": 4,
+                                                "startColumn": 17,
+                                                "endLine": 4,
+                                                "endColumn": 27,
+                                                "start": 109,
+                                                "end": 119
+                                            }
                                         },
-                                        "property": {
+                                        "location": {
+                                            "startLine": 4,
+                                            "startColumn": 17,
+                                            "endLine": 4,
+                                            "endColumn": 27,
+                                            "start": 109,
+                                            "end": 119
+                                        }
+                                    }
+                                ],
+                                "listeners": [],
+                                "children": [
+                                    {
+                                        "type": "Text",
+                                        "raw": "{index}",
+                                        "value": {
                                             "type": "Identifier",
-                                            "start": 21,
-                                            "end": 29,
-                                            "name": "toString"
+                                            "start": 1,
+                                            "end": 6,
+                                            "name": "index",
+                                            "location": {
+                                                "startLine": 4,
+                                                "startColumn": 28,
+                                                "endLine": 4,
+                                                "endColumn": 44,
+                                                "start": 120,
+                                                "end": 136
+                                            }
                                         },
-                                        "computed": false,
-                                        "optional": false
+                                        "location": {
+                                            "startLine": 4,
+                                            "startColumn": 28,
+                                            "endLine": 4,
+                                            "endColumn": 44,
+                                            "start": 120,
+                                            "end": 136
+                                        }
                                     },
-                                    "arguments": [],
-                                    "optional": false,
-                                    "location": {
-                                        "startLine": 3,
-                                        "startColumn": 47,
-                                        "endLine": 3,
-                                        "endColumn": 79,
-                                        "start": 71,
-                                        "end": 103
+                                    {
+                                        "type": "Text",
+                                        "raw": " - ",
+                                        "value": {
+                                            "type": "Literal",
+                                            "value": " - "
+                                        },
+                                        "location": {
+                                            "startLine": 4,
+                                            "startColumn": 28,
+                                            "endLine": 4,
+                                            "endColumn": 44,
+                                            "start": 120,
+                                            "end": 136
+                                        }
+                                    },
+                                    {
+                                        "type": "Text",
+                                        "raw": "{item}",
+                                        "value": {
+                                            "type": "Identifier",
+                                            "start": 11,
+                                            "end": 15,
+                                            "name": "item",
+                                            "location": {
+                                                "startLine": 4,
+                                                "startColumn": 28,
+                                                "endLine": 4,
+                                                "endColumn": 44,
+                                                "start": 120,
+                                                "end": 136
+                                            }
+                                        },
+                                        "location": {
+                                            "startLine": 4,
+                                            "startColumn": 28,
+                                            "endLine": 4,
+                                            "endColumn": 44,
+                                            "start": 120,
+                                            "end": 136
+                                        }
                                     }
-                                },
-                                "location": {
-                                    "startLine": 3,
-                                    "startColumn": 47,
-                                    "endLine": 3,
-                                    "endColumn": 79,
-                                    "start": 71,
-                                    "end": 103
-                                }
+                                ]
                             }
                         ]
                     }
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js
index 322fe089a7..79f05a68a1 100644
--- a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js
@@ -1,34 +1,33 @@
 import _implicitStylesheets from "./object-expr.css";
 import _implicitScopedStylesheets from "./object-expr.scoped.css?scoped=true";
-import _xPert from "x/pert";
-import { freezeTemplate, registerTemplate } from "lwc";
+import { freezeTemplate, parseFragment, registerTemplate } from "lwc";
+const $fragment1 = parseFragment`<li${3}>${"t1"}</li>`;
 const stc0 = {
   key: 0,
 };
-const stc1 = {
-  props: {
-    attr: {
-      obj: "literal",
-    },
-  },
-  key: 1,
-};
-const stc2 = {
-  obj: "literal",
-};
 function tmpl($api, $cmp, $slotset, $ctx) {
   const {
+    k: api_key,
     d: api_dynamic_text,
-    t: api_text,
-    c: api_custom_element,
+    sp: api_static_part,
+    st: api_static_fragment,
+    i: api_iterator,
     h: api_element,
   } = $api;
   return [
-    api_element("section", stc0, [
-      api_custom_element("x-pert", _xPert, stc1, [
-        api_text(api_dynamic_text(stc2.toString())),
-      ]),
-    ]),
+    api_element(
+      "ul",
+      stc0,
+      api_iterator($cmp.list(), function (item, index) {
+        return api_static_fragment($fragment1, api_key(2, item), [
+          api_static_part(
+            1,
+            null,
+            api_dynamic_text(index) + " - " + api_dynamic_text(item)
+          ),
+        ]);
+      })
+    ),
   ];
   /*LWC compiler vX.X.X*/
 }

From aaffccf99da182258a6dadc4f7fc20a7bb857c35 Mon Sep 17 00:00:00 2001
From: John Hefferman <jhefferman@salesforce.com>
Date: Wed, 24 Sep 2025 14:02:19 -0600
Subject: [PATCH 07/11] fix: additional testing around ssr specific codepaths

---
 .../expected-ssr.html                         |   6 +
 .../for-each-block/complex/config.json        |   8 +
 .../for-each-block/complex/error-ssr.txt      |   0
 .../fixtures/for-each-block/complex/error.txt |   1 +
 .../for-each-block/complex/expected-ssr.html  |  15 +
 .../for-each-block/complex/expected.html      |   0
 .../x/for-each-block/for-each-block.html      |   7 +
 .../x/for-each-block/for-each-block.js        |   7 +
 .../fixtures/lwc-if-else-complex/config.json  |   8 +
 .../lwc-if-else-complex/error-ssr.txt         |   0
 .../fixtures/lwc-if-else-complex/error.txt    |   1 +
 .../lwc-if-else-complex/expected-ssr.html     |  10 +
 .../lwc-if-else-complex/expected.html         |   0
 .../modules/x/component/component.html        |  15 +
 .../modules/x/component/component.js          |  11 +
 .../fixtures/scoped-slots/complex/config.json |   8 +
 .../scoped-slots/complex/error-ssr.txt        |   0
 .../fixtures/scoped-slots/complex/error.txt   |   1 +
 .../scoped-slots/complex/expected-ssr.html    |  15 +
 .../scoped-slots/complex/expected.html        |   0
 .../modules/x/complexChild/complexChild.html  |   5 +
 .../modules/x/complexChild/complexChild.js    |   8 +
 .../x/complexParent/complexParent.html        |   7 +
 .../modules/x/complexParent/complexParent.js  |   3 +
 .../expected-ssr.html                         |   7 +
 .../valid/object-expr/actual.html             |  10 +-
 .../valid/object-expr/ast.json                | 349 ++++++++----------
 .../valid/object-expr/expected.js             |  39 +-
 28 files changed, 321 insertions(+), 220 deletions(-)
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected-ssr.html
 create mode 100755 packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/config.json
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/error-ssr.txt
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/error.txt
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/expected-ssr.html
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/expected.html
 create mode 100755 packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/modules/x/for-each-block/for-each-block.html
 create mode 100755 packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/modules/x/for-each-block/for-each-block.js
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/config.json
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/error-ssr.txt
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/error.txt
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/expected-ssr.html
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/expected.html
 create mode 100755 packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/modules/x/component/component.html
 create mode 100755 packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/modules/x/component/component.js
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/config.json
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/error-ssr.txt
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/error.txt
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/expected-ssr.html
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/expected.html
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexChild/complexChild.html
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexChild/complexChild.js
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexParent/complexParent.html
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexParent/complexParent.js
 create mode 100644 packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected-ssr.html

diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected-ssr.html b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected-ssr.html
new file mode 100644
index 0000000000..259866046b
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/attribute-dynamic-complex/expected-ssr.html
@@ -0,0 +1,6 @@
+<fixture-test>
+  <template shadowrootmode="open">
+    <div class="foobar">
+    </div>
+  </template>
+</fixture-test>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/config.json b/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/config.json
new file mode 100755
index 0000000000..b302e68ad6
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/config.json
@@ -0,0 +1,8 @@
+{
+    "entry": "x/for-each-block",
+    "experimentalComplexExpressions": true,
+    "ssrFiles": {
+        "expected": "expected-ssr.html",
+        "error": "error-ssr.txt"
+    }
+}
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/error-ssr.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/error-ssr.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/error.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/error.txt
new file mode 100644
index 0000000000..f13176a7a6
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/error.txt
@@ -0,0 +1 @@
+LWC1034: Ambiguous attribute value for:each="{list()}". If you want to make it a valid identifier you should remove the surrounding quotes for:each={list()}. If you want to make it a string you should escape it for:each="\{list()}".
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/expected-ssr.html b/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/expected-ssr.html
new file mode 100644
index 0000000000..3b62ecf650
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/expected-ssr.html
@@ -0,0 +1,15 @@
+<fixture-test>
+  <template shadowrootmode="open">
+    <ul>
+      <li>
+        0 - paris
+      </li>
+      <li>
+        1 - london
+      </li>
+      <li>
+        2 - tokyo
+      </li>
+    </ul>
+  </template>
+</fixture-test>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/expected.html b/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/expected.html
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/modules/x/for-each-block/for-each-block.html b/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/modules/x/for-each-block/for-each-block.html
new file mode 100755
index 0000000000..664b217367
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/modules/x/for-each-block/for-each-block.html
@@ -0,0 +1,7 @@
+<template>
+    <ul>
+        <template for:each="{list()}" for:item="item" for:index="index">
+            <li key={item}>{index} - {item}</li>
+        </template>
+    </ul>
+</template>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/modules/x/for-each-block/for-each-block.js b/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/modules/x/for-each-block/for-each-block.js
new file mode 100755
index 0000000000..4a98edc205
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/for-each-block/complex/modules/x/for-each-block/for-each-block.js
@@ -0,0 +1,7 @@
+import { LightningElement } from 'lwc';
+
+export default class Component extends LightningElement {
+    list() {
+        return ['paris', 'london', 'tokyo'];
+    }
+}
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/config.json b/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/config.json
new file mode 100644
index 0000000000..74eaaf0c4f
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/config.json
@@ -0,0 +1,8 @@
+{
+    "entry": "x/component",
+    "experimentalComplexExpressions": true,
+    "ssrFiles": {
+        "expected": "expected-ssr.html",
+        "error": "error-ssr.txt"
+    }
+}
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/error-ssr.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/error-ssr.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/error.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/error.txt
new file mode 100644
index 0000000000..1f6547bdc5
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/error.txt
@@ -0,0 +1 @@
+LWC1034: Ambiguous attribute value lwc:if="{isTrue()}". If you want to make it a valid identifier you should remove the surrounding quotes lwc:if={isTrue()}. If you want to make it a string you should escape it lwc:if="\{isTrue()}".
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/expected-ssr.html b/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/expected-ssr.html
new file mode 100644
index 0000000000..3985fdcdf6
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/expected-ssr.html
@@ -0,0 +1,10 @@
+<fixture-test>
+  <template shadowrootmode="open">
+    <!---->
+    I am true!
+    <!---->
+    <!---->
+    I am not false!
+    <!---->
+  </template>
+</fixture-test>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/expected.html b/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/expected.html
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/modules/x/component/component.html b/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/modules/x/component/component.html
new file mode 100755
index 0000000000..83717eb733
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/modules/x/component/component.html
@@ -0,0 +1,15 @@
+<template>
+    <template lwc:if="{isTrue()}">
+        I am true!
+    </template>
+    <template lwc:else>
+        I am not true!
+    </template>
+
+    <template lwc:if="{isFalse()}">
+        I am false!
+    </template>
+    <template lwc:else>
+        I am not false!
+    </template>
+</template>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/modules/x/component/component.js b/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/modules/x/component/component.js
new file mode 100755
index 0000000000..ee524af201
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/lwc-if-else-complex/modules/x/component/component.js
@@ -0,0 +1,11 @@
+import { LightningElement } from 'lwc';
+
+export default class IfBlock extends LightningElement {
+    isTrue() {
+        return true;
+    }
+
+    isFalse() {
+        return this.false;
+    }
+}
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/config.json b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/config.json
new file mode 100644
index 0000000000..045b0db31b
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/config.json
@@ -0,0 +1,8 @@
+{
+    "entry": "x/complexParent",
+    "experimentalComplexExpressions": true,
+    "ssrFiles": {
+        "expected": "expected-ssr.html",
+        "error": "error-ssr.txt"
+    }
+}
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/error-ssr.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/error-ssr.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/error.txt b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/error.txt
new file mode 100644
index 0000000000..a4bc6c6950
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/error.txt
@@ -0,0 +1 @@
+LWC1060: Template expression doesn't allow CallExpression
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/expected-ssr.html b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/expected-ssr.html
new file mode 100644
index 0000000000..63dd5a68eb
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/expected-ssr.html
@@ -0,0 +1,15 @@
+<fixture-test>
+  <template shadowrootmode="open">
+    <x-complex-child>
+      <div>
+        <!---->
+        <!---->
+        <span>
+          99 - ssr
+        </span>
+        <!---->
+        <!---->
+      </div>
+    </x-complex-child>
+  </template>
+</fixture-test>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/expected.html b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/expected.html
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexChild/complexChild.html b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexChild/complexChild.html
new file mode 100644
index 0000000000..c624f74879
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexChild/complexChild.html
@@ -0,0 +1,5 @@
+<template lwc:render-mode="light">
+    <div>
+        <slot lwc:slot-bind="{itemFn()}">Default slot content</slot>
+    </div>
+</template>
\ No newline at end of file
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexChild/complexChild.js b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexChild/complexChild.js
new file mode 100644
index 0000000000..c5970cfa44
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexChild/complexChild.js
@@ -0,0 +1,8 @@
+import { LightningElement } from 'lwc';
+
+export default class Child extends LightningElement {
+    static renderMode = 'light';
+    itemFn() {
+        return () => ({ id: 99, name: 'ssr' });
+    }
+}
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexParent/complexParent.html b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexParent/complexParent.html
new file mode 100644
index 0000000000..fda7fb7d7d
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexParent/complexParent.html
@@ -0,0 +1,7 @@
+<template>
+    <x-complex-child>
+        <template lwc:slot-data="itemFn">
+            <span>{itemFn().id} - {itemFn().name}</span>
+        </template>
+    </x-complex-child>
+</template>
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexParent/complexParent.js b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexParent/complexParent.js
new file mode 100644
index 0000000000..a5746a015a
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/scoped-slots/complex/modules/x/complexParent/complexParent.js
@@ -0,0 +1,3 @@
+import { LightningElement } from 'lwc';
+
+export default class Parent extends LightningElement {}
diff --git a/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected-ssr.html b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected-ssr.html
new file mode 100644
index 0000000000..68f5d530f9
--- /dev/null
+++ b/packages/@lwc/engine-server/src/__tests__/fixtures/text-interpolation-complex/expected-ssr.html
@@ -0,0 +1,7 @@
+<fixture-test>
+  <template shadowrootmode="open">
+    <p>
+      foo bar bar foo
+    </p>
+  </template>
+</fixture-test>
\ No newline at end of file
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html
index 664b217367..a594536bea 100644
--- a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/actual.html
@@ -1,7 +1,5 @@
 <template>
-    <ul>
-        <template for:each="{list()}" for:item="item" for:index="index">
-            <li key={item}>{index} - {item}</li>
-        </template>
-    </ul>
-</template>
\ No newline at end of file
+    <section>
+        <x-pert attr="{({ obj: 'literal' })}">{({ obj: 'literal'}).toString()}</x-pert>
+    </section>
+</template>
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json
index 52c9d119bb..79af6ab260 100644
--- a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/ast.json
@@ -4,10 +4,10 @@
         "location": {
             "startLine": 1,
             "startColumn": 1,
-            "endLine": 7,
+            "endLine": 5,
             "endColumn": 12,
             "start": 0,
-            "end": 183,
+            "end": 139,
             "startTag": {
                 "startLine": 1,
                 "startColumn": 1,
@@ -17,42 +17,42 @@
                 "end": 10
             },
             "endTag": {
-                "startLine": 7,
+                "startLine": 5,
                 "startColumn": 1,
-                "endLine": 7,
+                "endLine": 5,
                 "endColumn": 12,
-                "start": 172,
-                "end": 183
+                "start": 128,
+                "end": 139
             }
         },
         "directives": [],
         "children": [
             {
                 "type": "Element",
-                "name": "ul",
+                "name": "section",
                 "namespace": "http://www.w3.org/1999/xhtml",
                 "location": {
                     "startLine": 2,
                     "startColumn": 5,
-                    "endLine": 6,
-                    "endColumn": 10,
+                    "endLine": 4,
+                    "endColumn": 15,
                     "start": 15,
-                    "end": 171,
+                    "end": 127,
                     "startTag": {
                         "startLine": 2,
                         "startColumn": 5,
                         "endLine": 2,
-                        "endColumn": 9,
+                        "endColumn": 14,
                         "start": 15,
-                        "end": 19
+                        "end": 24
                     },
                     "endTag": {
-                        "startLine": 6,
+                        "startLine": 4,
                         "startColumn": 5,
-                        "endLine": 6,
-                        "endColumn": 10,
-                        "start": 166,
-                        "end": 171
+                        "endLine": 4,
+                        "endColumn": 15,
+                        "start": 117,
+                        "end": 127
                     }
                 },
                 "attributes": [],
@@ -61,198 +61,157 @@
                 "listeners": [],
                 "children": [
                     {
-                        "type": "ForEach",
-                        "expression": {
-                            "type": "CallExpression",
-                            "start": 1,
-                            "end": 7,
-                            "callee": {
-                                "type": "Identifier",
-                                "start": 1,
-                                "end": 5,
-                                "name": "list"
-                            },
-                            "arguments": [],
-                            "optional": false,
-                            "location": {
-                                "startLine": 3,
-                                "startColumn": 19,
-                                "endLine": 3,
-                                "endColumn": 38,
-                                "start": 38,
-                                "end": 57
-                            }
-                        },
-                        "item": {
-                            "type": "Identifier",
-                            "name": "item",
-                            "location": {
+                        "type": "Component",
+                        "name": "x-pert",
+                        "namespace": "http://www.w3.org/1999/xhtml",
+                        "location": {
+                            "startLine": 3,
+                            "startColumn": 9,
+                            "endLine": 3,
+                            "endColumn": 88,
+                            "start": 33,
+                            "end": 112,
+                            "startTag": {
                                 "startLine": 3,
-                                "startColumn": 39,
+                                "startColumn": 9,
                                 "endLine": 3,
-                                "endColumn": 54,
-                                "start": 58,
-                                "end": 73
-                            }
-                        },
-                        "index": {
-                            "type": "Identifier",
-                            "name": "index",
-                            "location": {
+                                "endColumn": 47,
+                                "start": 33,
+                                "end": 71
+                            },
+                            "endTag": {
                                 "startLine": 3,
-                                "startColumn": 55,
+                                "startColumn": 79,
                                 "endLine": 3,
-                                "endColumn": 72,
-                                "start": 74,
-                                "end": 91
+                                "endColumn": 88,
+                                "start": 103,
+                                "end": 112
                             }
                         },
-                        "location": {
-                            "startLine": 3,
-                            "startColumn": 9,
-                            "endLine": 5,
-                            "endColumn": 20,
-                            "start": 28,
-                            "end": 161
-                        },
-                        "directiveLocation": {
-                            "startLine": 3,
-                            "startColumn": 19,
-                            "endLine": 3,
-                            "endColumn": 38,
-                            "start": 38,
-                            "end": 57
-                        },
-                        "children": [
+                        "attributes": [],
+                        "properties": [
                             {
-                                "type": "Element",
-                                "name": "li",
-                                "namespace": "http://www.w3.org/1999/xhtml",
-                                "location": {
-                                    "startLine": 4,
-                                    "startColumn": 13,
-                                    "endLine": 4,
-                                    "endColumn": 49,
-                                    "start": 105,
-                                    "end": 141,
-                                    "startTag": {
-                                        "startLine": 4,
-                                        "startColumn": 13,
-                                        "endLine": 4,
-                                        "endColumn": 28,
-                                        "start": 105,
-                                        "end": 120
-                                    },
-                                    "endTag": {
-                                        "startLine": 4,
-                                        "startColumn": 44,
-                                        "endLine": 4,
-                                        "endColumn": 49,
-                                        "start": 136,
-                                        "end": 141
+                                "type": "Property",
+                                "name": "attr",
+                                "attributeName": "attr",
+                                "value": {
+                                    "type": "ObjectExpression",
+                                    "start": 2,
+                                    "end": 20,
+                                    "properties": [
+                                        {
+                                            "type": "Property",
+                                            "start": 4,
+                                            "end": 18,
+                                            "method": false,
+                                            "shorthand": false,
+                                            "computed": false,
+                                            "key": {
+                                                "type": "Identifier",
+                                                "start": 4,
+                                                "end": 7,
+                                                "name": "obj"
+                                            },
+                                            "value": {
+                                                "type": "Literal",
+                                                "start": 9,
+                                                "end": 18,
+                                                "value": "literal",
+                                                "raw": "'literal'"
+                                            },
+                                            "kind": "init"
+                                        }
+                                    ],
+                                    "location": {
+                                        "startLine": 3,
+                                        "startColumn": 17,
+                                        "endLine": 3,
+                                        "endColumn": 46,
+                                        "start": 41,
+                                        "end": 70
                                     }
                                 },
-                                "attributes": [],
-                                "properties": [],
-                                "directives": [
-                                    {
-                                        "type": "Directive",
-                                        "name": "Key",
-                                        "value": {
-                                            "type": "Identifier",
-                                            "start": 1,
-                                            "end": 5,
-                                            "name": "item",
-                                            "location": {
-                                                "startLine": 4,
-                                                "startColumn": 17,
-                                                "endLine": 4,
-                                                "endColumn": 27,
-                                                "start": 109,
-                                                "end": 119
-                                            }
+                                "location": {
+                                    "startLine": 3,
+                                    "startColumn": 17,
+                                    "endLine": 3,
+                                    "endColumn": 46,
+                                    "start": 41,
+                                    "end": 70
+                                }
+                            }
+                        ],
+                        "directives": [],
+                        "listeners": [],
+                        "children": [
+                            {
+                                "type": "Text",
+                                "raw": "{({ obj: 'literal'}).toString()}",
+                                "value": {
+                                    "type": "CallExpression",
+                                    "start": 1,
+                                    "end": 31,
+                                    "callee": {
+                                        "type": "MemberExpression",
+                                        "start": 1,
+                                        "end": 29,
+                                        "object": {
+                                            "type": "ObjectExpression",
+                                            "start": 2,
+                                            "end": 19,
+                                            "properties": [
+                                                {
+                                                    "type": "Property",
+                                                    "start": 4,
+                                                    "end": 18,
+                                                    "method": false,
+                                                    "shorthand": false,
+                                                    "computed": false,
+                                                    "key": {
+                                                        "type": "Identifier",
+                                                        "start": 4,
+                                                        "end": 7,
+                                                        "name": "obj"
+                                                    },
+                                                    "value": {
+                                                        "type": "Literal",
+                                                        "start": 9,
+                                                        "end": 18,
+                                                        "value": "literal",
+                                                        "raw": "'literal'"
+                                                    },
+                                                    "kind": "init"
+                                                }
+                                            ]
                                         },
-                                        "location": {
-                                            "startLine": 4,
-                                            "startColumn": 17,
-                                            "endLine": 4,
-                                            "endColumn": 27,
-                                            "start": 109,
-                                            "end": 119
-                                        }
-                                    }
-                                ],
-                                "listeners": [],
-                                "children": [
-                                    {
-                                        "type": "Text",
-                                        "raw": "{index}",
-                                        "value": {
+                                        "property": {
                                             "type": "Identifier",
-                                            "start": 1,
-                                            "end": 6,
-                                            "name": "index",
-                                            "location": {
-                                                "startLine": 4,
-                                                "startColumn": 28,
-                                                "endLine": 4,
-                                                "endColumn": 44,
-                                                "start": 120,
-                                                "end": 136
-                                            }
+                                            "start": 21,
+                                            "end": 29,
+                                            "name": "toString"
                                         },
-                                        "location": {
-                                            "startLine": 4,
-                                            "startColumn": 28,
-                                            "endLine": 4,
-                                            "endColumn": 44,
-                                            "start": 120,
-                                            "end": 136
-                                        }
+                                        "computed": false,
+                                        "optional": false
                                     },
-                                    {
-                                        "type": "Text",
-                                        "raw": " - ",
-                                        "value": {
-                                            "type": "Literal",
-                                            "value": " - "
-                                        },
-                                        "location": {
-                                            "startLine": 4,
-                                            "startColumn": 28,
-                                            "endLine": 4,
-                                            "endColumn": 44,
-                                            "start": 120,
-                                            "end": 136
-                                        }
-                                    },
-                                    {
-                                        "type": "Text",
-                                        "raw": "{item}",
-                                        "value": {
-                                            "type": "Identifier",
-                                            "start": 11,
-                                            "end": 15,
-                                            "name": "item",
-                                            "location": {
-                                                "startLine": 4,
-                                                "startColumn": 28,
-                                                "endLine": 4,
-                                                "endColumn": 44,
-                                                "start": 120,
-                                                "end": 136
-                                            }
-                                        },
-                                        "location": {
-                                            "startLine": 4,
-                                            "startColumn": 28,
-                                            "endLine": 4,
-                                            "endColumn": 44,
-                                            "start": 120,
-                                            "end": 136
-                                        }
+                                    "arguments": [],
+                                    "optional": false,
+                                    "location": {
+                                        "startLine": 3,
+                                        "startColumn": 47,
+                                        "endLine": 3,
+                                        "endColumn": 79,
+                                        "start": 71,
+                                        "end": 103
                                     }
-                                ]
+                                },
+                                "location": {
+                                    "startLine": 3,
+                                    "startColumn": 47,
+                                    "endLine": 3,
+                                    "endColumn": 79,
+                                    "start": 71,
+                                    "end": 103
+                                }
                             }
                         ]
                     }
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js
index 79f05a68a1..322fe089a7 100644
--- a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/valid/object-expr/expected.js
@@ -1,33 +1,34 @@
 import _implicitStylesheets from "./object-expr.css";
 import _implicitScopedStylesheets from "./object-expr.scoped.css?scoped=true";
-import { freezeTemplate, parseFragment, registerTemplate } from "lwc";
-const $fragment1 = parseFragment`<li${3}>${"t1"}</li>`;
+import _xPert from "x/pert";
+import { freezeTemplate, registerTemplate } from "lwc";
 const stc0 = {
   key: 0,
 };
+const stc1 = {
+  props: {
+    attr: {
+      obj: "literal",
+    },
+  },
+  key: 1,
+};
+const stc2 = {
+  obj: "literal",
+};
 function tmpl($api, $cmp, $slotset, $ctx) {
   const {
-    k: api_key,
     d: api_dynamic_text,
-    sp: api_static_part,
-    st: api_static_fragment,
-    i: api_iterator,
+    t: api_text,
+    c: api_custom_element,
     h: api_element,
   } = $api;
   return [
-    api_element(
-      "ul",
-      stc0,
-      api_iterator($cmp.list(), function (item, index) {
-        return api_static_fragment($fragment1, api_key(2, item), [
-          api_static_part(
-            1,
-            null,
-            api_dynamic_text(index) + " - " + api_dynamic_text(item)
-          ),
-        ]);
-      })
-    ),
+    api_element("section", stc0, [
+      api_custom_element("x-pert", _xPert, stc1, [
+        api_text(api_dynamic_text(stc2.toString())),
+      ]),
+    ]),
   ];
   /*LWC compiler vX.X.X*/
 }

From a8b5f8810b8421b18175104938fb6633d2f49f71 Mon Sep 17 00:00:00 2001
From: John Hefferman <jhefferman@salesforce.com>
Date: Mon, 29 Sep 2025 09:10:02 -0600
Subject: [PATCH 08/11] feat: api specific errors, tests

---
 .../errors/src/compiler/error-info/index.ts   |  2 +-
 .../compiler/error-info/template-transform.ts | 20 ++++-
 packages/@lwc/shared/src/api-version.ts       | 48 ++++++-----
 .../src/__tests__/fixtures.spec.ts            |  2 +-
 .../src/compile-template/expression.ts        | 11 ++-
 .../src/compile-template/index.ts             |  2 +
 .../src/compile-template/types.ts             |  1 +
 .../actual.html                               |  5 ++
 .../ast.json                                  |  1 +
 .../config.json                               |  4 +
 .../expected.js                               |  0
 .../metadata.json                             | 15 ++++
 .../actual.html                               |  5 ++
 .../ast.json                                  |  1 +
 .../config.json                               |  4 +
 .../expected.js                               |  0
 .../metadata.json                             | 15 ++++
 .../actual.html                               |  5 ++
 .../ast.json                                  |  1 +
 .../config.json                               |  4 +
 .../expected.js                               |  0
 .../metadata.json                             | 15 ++++
 .../actual.html                               |  3 +
 .../ast.json                                  |  1 +
 .../config.json                               |  4 +
 .../expected.js                               |  0
 .../metadata.json                             | 15 ++++
 .../template-compiler/src/parser/attribute.ts |  6 +-
 .../src/parser/expression.ts                  | 81 +++++++++++++------
 .../template-compiler/src/parser/index.ts     | 10 +--
 30 files changed, 225 insertions(+), 56 deletions(-)
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/actual.html
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/ast.json
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/config.json
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/expected.js
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/metadata.json
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/actual.html
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/ast.json
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/config.json
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/expected.js
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/metadata.json
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/actual.html
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/ast.json
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/config.json
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/expected.js
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/metadata.json
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/actual.html
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/ast.json
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/config.json
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/expected.js
 create mode 100644 packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/metadata.json

diff --git a/packages/@lwc/errors/src/compiler/error-info/index.ts b/packages/@lwc/errors/src/compiler/error-info/index.ts
index 4129bedf60..ac79220451 100644
--- a/packages/@lwc/errors/src/compiler/error-info/index.ts
+++ b/packages/@lwc/errors/src/compiler/error-info/index.ts
@@ -5,7 +5,7 @@
  * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
  */
 /**
- * Next error code: 1209
+ * Next error code: 1211
  */
 
 export * from './compiler';
diff --git a/packages/@lwc/errors/src/compiler/error-info/template-transform.ts b/packages/@lwc/errors/src/compiler/error-info/template-transform.ts
index 70fa8f14b0..d3a6729647 100644
--- a/packages/@lwc/errors/src/compiler/error-info/template-transform.ts
+++ b/packages/@lwc/errors/src/compiler/error-info/template-transform.ts
@@ -980,7 +980,7 @@ export const ParserDiagnostics = {
         url: '',
     },
 
-    COMPUTED_PROPERTY_ACCESS_NOT_ALLOWED_COMPLEX: {
+    COMPUTED_PROPERTY_ACCESS_NOT_ALLOWED_CTE_UNQUOTED: {
         code: 1207,
         message:
             'Template expression doesn\'t allow computed property access unless the expression is surrounded by quotes: "{0}"',
@@ -988,11 +988,27 @@ export const ParserDiagnostics = {
         url: '',
     },
 
-    INVALID_NODE_COMPLEX: {
+    INVALID_NODE_CTE_UNQUOTED: {
         code: 1208,
         message:
             'Template expression doesn\'t allow {0} unless the expression is surrounded by quotes: "{1}"',
         level: DiagnosticLevel.Error,
         url: '',
     },
+
+    COMPUTED_PROPERTY_ACCESS_NOT_ALLOWED_CTE_API_VERSION: {
+        code: 1209,
+        message:
+            "Template expression doesn't allow computed property access. The current component API version ({1}) is insufficient and must be increased to at least {2} for this type of expression.",
+        level: DiagnosticLevel.Error,
+        url: '',
+    },
+
+    INVALID_NODE_CTE_API_VERSION: {
+        code: 1210,
+        message:
+            "Template expression doesn't allow {0}. The current component API version ({1}) is insufficient and must be increased to at least {2} for this type of expression.",
+        level: DiagnosticLevel.Error,
+        url: '',
+    },
 };
diff --git a/packages/@lwc/shared/src/api-version.ts b/packages/@lwc/shared/src/api-version.ts
index 72bc130103..becdd472cc 100644
--- a/packages/@lwc/shared/src/api-version.ts
+++ b/packages/@lwc/shared/src/api-version.ts
@@ -14,6 +14,9 @@ export const enum APIVersion {
     V61_250_SUMMER_24 = 61,
     V62_252_WINTER_25 = 62,
     V63_254_SPRING_25 = 63,
+    V64_256_SUMMER_25 = 64,
+    V65_258_WINTER_26 = 65,
+    V66_260_SPRING_26 = 66,
 }
 
 // These must be updated when the enum is updated.
@@ -27,6 +30,9 @@ const allVersions = [
     APIVersion.V61_250_SUMMER_24,
     APIVersion.V62_252_WINTER_25,
     APIVersion.V63_254_SPRING_25,
+    APIVersion.V64_256_SUMMER_25,
+    APIVersion.V65_258_WINTER_26,
+    APIVersion.V66_260_SPRING_26,
 ];
 const allVersionsSet = /*@__PURE__@*/ new Set(allVersions);
 export const LOWEST_API_VERSION = allVersions[0];
@@ -117,6 +123,28 @@ export const enum APIFeature {
     ENABLE_COMPLEX_TEMPLATE_EXPRESSIONS,
 }
 
+const minFeatureApiVersions = new Map([
+    [APIFeature.LOWERCASE_SCOPE_TOKENS, APIVersion.V59_246_WINTER_24],
+    [APIFeature.TREAT_ALL_PARSE5_ERRORS_AS_ERRORS, APIVersion.V59_246_WINTER_24],
+    [APIFeature.DISABLE_OBJECT_REST_SPREAD_TRANSFORMATION, APIVersion.V60_248_SPRING_24],
+    [APIFeature.SKIP_UNNECESSARY_REGISTER_DECORATORS, APIVersion.V60_248_SPRING_24],
+    [APIFeature.USE_COMMENTS_FOR_FRAGMENT_BOOKENDS, APIVersion.V60_248_SPRING_24],
+    [APIFeature.USE_FRAGMENTS_FOR_LIGHT_DOM_SLOTS, APIVersion.V60_248_SPRING_24],
+    [APIFeature.ENABLE_ELEMENT_INTERNALS_AND_FACE, APIVersion.V61_250_SUMMER_24],
+    [APIFeature.USE_LIGHT_DOM_SLOT_FORWARDING, APIVersion.V61_250_SUMMER_24],
+    [APIFeature.ENABLE_THIS_DOT_HOST_ELEMENT, APIVersion.V62_252_WINTER_25],
+    [APIFeature.ENABLE_THIS_DOT_STYLE, APIVersion.V62_252_WINTER_25],
+    [APIFeature.TEMPLATE_CLASS_NAME_OBJECT_BINDING, APIVersion.V62_252_WINTER_25],
+    [APIFeature.ENABLE_COMPLEX_TEMPLATE_EXPRESSIONS, APIVersion.V66_260_SPRING_26],
+]);
+
+/**
+ * @param apiVersionFeature
+ */
+export function minApiVersion(apiVersionFeature: APIFeature): APIVersion {
+    return minFeatureApiVersions.get(apiVersionFeature) || HIGHEST_API_VERSION;
+}
+
 /**
  *
  * @param apiVersionFeature
@@ -126,23 +154,5 @@ export function isAPIFeatureEnabled(
     apiVersionFeature: APIFeature,
     apiVersion: APIVersion
 ): boolean {
-    switch (apiVersionFeature) {
-        case APIFeature.LOWERCASE_SCOPE_TOKENS:
-        case APIFeature.TREAT_ALL_PARSE5_ERRORS_AS_ERRORS:
-            return apiVersion >= APIVersion.V59_246_WINTER_24;
-        case APIFeature.DISABLE_OBJECT_REST_SPREAD_TRANSFORMATION:
-        case APIFeature.SKIP_UNNECESSARY_REGISTER_DECORATORS:
-        case APIFeature.USE_COMMENTS_FOR_FRAGMENT_BOOKENDS:
-        case APIFeature.USE_FRAGMENTS_FOR_LIGHT_DOM_SLOTS:
-            return apiVersion >= APIVersion.V60_248_SPRING_24;
-        case APIFeature.ENABLE_ELEMENT_INTERNALS_AND_FACE:
-        case APIFeature.USE_LIGHT_DOM_SLOT_FORWARDING:
-            return apiVersion >= APIVersion.V61_250_SUMMER_24;
-        case APIFeature.ENABLE_THIS_DOT_HOST_ELEMENT:
-        case APIFeature.ENABLE_THIS_DOT_STYLE:
-        case APIFeature.TEMPLATE_CLASS_NAME_OBJECT_BINDING:
-            return apiVersion >= APIVersion.V62_252_WINTER_25;
-        case APIFeature.ENABLE_COMPLEX_TEMPLATE_EXPRESSIONS:
-            return apiVersion >= APIVersion.V63_254_SPRING_25;
-    }
+    return apiVersion >= minApiVersion(apiVersionFeature);
 }
diff --git a/packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts b/packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts
index 0af9fa2537..559a30ae3d 100644
--- a/packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts
+++ b/packages/@lwc/ssr-compiler/src/__tests__/fixtures.spec.ts
@@ -61,7 +61,7 @@ async function compileFixture({
 }: {
     entry: string;
     dirname: string;
-    experimentalComplexExpressions: boolean;
+    experimentalComplexExpressions: boolean | undefined;
 }) {
     const modulesDir = path.resolve(dirname, './modules');
     const outputFile = path.resolve(dirname, './dist/compiled-experimental-ssr.js');
diff --git a/packages/@lwc/ssr-compiler/src/compile-template/expression.ts b/packages/@lwc/ssr-compiler/src/compile-template/expression.ts
index f554571f12..e2e764ae54 100644
--- a/packages/@lwc/ssr-compiler/src/compile-template/expression.ts
+++ b/packages/@lwc/ssr-compiler/src/compile-template/expression.ts
@@ -5,6 +5,7 @@
  * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
  */
 import { bindExpression } from '@lwc/template-compiler';
+import { APIFeature, isAPIFeatureEnabled } from '@lwc/shared';
 import type {
     ComplexExpression as IrComplexExpression,
     Expression as IrExpression,
@@ -18,11 +19,17 @@ export function expressionIrToEs(
     node: IrExpression | IrComplexExpression,
     cxt: TransformerContext
 ): EsExpression {
+    const isComplexTemplateExpressionEnabled =
+        cxt.templateOptions.experimentalComplexExpressions &&
+        isAPIFeatureEnabled(
+            APIFeature.ENABLE_COMPLEX_TEMPLATE_EXPRESSIONS,
+            cxt.templateOptions.apiVersion
+        );
     return bindExpression(
         node as IrComplexExpression,
-        (n: EsIdentifier) => cxt.isLocalVar((n as EsIdentifier).name),
+        (n: EsIdentifier) => cxt.isLocalVar(n.name),
         'instance',
-        cxt.templateOptions.experimentalComplexExpressions
+        isComplexTemplateExpressionEnabled
     );
 }
 
diff --git a/packages/@lwc/ssr-compiler/src/compile-template/index.ts b/packages/@lwc/ssr-compiler/src/compile-template/index.ts
index c07acc51b1..cd9c1784b8 100644
--- a/packages/@lwc/ssr-compiler/src/compile-template/index.ts
+++ b/packages/@lwc/ssr-compiler/src/compile-template/index.ts
@@ -116,10 +116,12 @@ export default function compileTemplate(
         (directive) => directive.name === 'PreserveComments'
     )?.value?.value;
     const experimentalComplexExpressions = Boolean(options.experimentalComplexExpressions);
+    const apiVersion = Number(options.apiVersion);
 
     const { addImport, getImports, statements, cxt } = templateIrToEsTree(root, {
         preserveComments,
         experimentalComplexExpressions,
+        apiVersion,
     });
     addImport(['renderStylesheets', 'hasScopedStaticStylesheets']);
     for (const [imports, source] of getStylesheetImports(filename)) {
diff --git a/packages/@lwc/ssr-compiler/src/compile-template/types.ts b/packages/@lwc/ssr-compiler/src/compile-template/types.ts
index 73f244a87d..385132bd78 100644
--- a/packages/@lwc/ssr-compiler/src/compile-template/types.ts
+++ b/packages/@lwc/ssr-compiler/src/compile-template/types.ts
@@ -48,4 +48,5 @@ export interface TransformerContext {
 export interface TemplateOpts {
     preserveComments: boolean;
     experimentalComplexExpressions: boolean;
+    apiVersion: number;
 }
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/actual.html b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/actual.html
new file mode 100644
index 0000000000..c392a95ca2
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/actual.html
@@ -0,0 +1,5 @@
+<template>
+    <section>
+        <x-child foo="{foo()}"></x-child>
+    </section>
+</template>
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/ast.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/ast.json
new file mode 100644
index 0000000000..9e26dfeeb6
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/ast.json
@@ -0,0 +1 @@
+{}
\ No newline at end of file
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/config.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/config.json
new file mode 100644
index 0000000000..00f1c239e3
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/config.json
@@ -0,0 +1,4 @@
+{
+    "experimentalComplexExpressions": true,
+    "apiVersion": 59
+}
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/expected.js b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/expected.js
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/metadata.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/metadata.json
new file mode 100644
index 0000000000..ba8bf0fe67
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-attribute/metadata.json
@@ -0,0 +1,15 @@
+{
+    "warnings": [
+        {
+            "code": 1210,
+            "message": "Invalid expression {foo()} - LWC1210: Template expression doesn't allow CallExpression. The current component API version (59) is insufficient and must be increased to at least 66 for this type of expression.",
+            "level": 1,
+            "location": {
+                "line": 3,
+                "column": 18,
+                "start": 42,
+                "length": 13
+            }
+        }
+    ]
+}
\ No newline at end of file
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/actual.html b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/actual.html
new file mode 100644
index 0000000000..e05f5f409c
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/actual.html
@@ -0,0 +1,5 @@
+<template>
+    <section>
+        <x-child>{foo()}</x-child>
+    </section>
+</template>
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/ast.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/ast.json
new file mode 100644
index 0000000000..9e26dfeeb6
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/ast.json
@@ -0,0 +1 @@
+{}
\ No newline at end of file
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/config.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/config.json
new file mode 100644
index 0000000000..00f1c239e3
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/config.json
@@ -0,0 +1,4 @@
+{
+    "experimentalComplexExpressions": true,
+    "apiVersion": 59
+}
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/expected.js b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/expected.js
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/metadata.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/metadata.json
new file mode 100644
index 0000000000..d09517a49b
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-call-expr-text-node/metadata.json
@@ -0,0 +1,15 @@
+{
+    "warnings": [
+        {
+            "code": 1210,
+            "message": "Invalid expression {foo()} - LWC1210: Template expression doesn't allow CallExpression. The current component API version (59) is insufficient and must be increased to at least 66 for this type of expression.",
+            "level": 1,
+            "location": {
+                "line": 3,
+                "column": 18,
+                "start": 42,
+                "length": 7
+            }
+        }
+    ]
+}
\ No newline at end of file
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/actual.html b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/actual.html
new file mode 100644
index 0000000000..2afc794893
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/actual.html
@@ -0,0 +1,5 @@
+<template>
+    <section>
+        <p class="{classNames[0]}"></p>
+    </section>
+</template>
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/ast.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/ast.json
new file mode 100644
index 0000000000..9e26dfeeb6
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/ast.json
@@ -0,0 +1 @@
+{}
\ No newline at end of file
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/config.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/config.json
new file mode 100644
index 0000000000..00f1c239e3
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/config.json
@@ -0,0 +1,4 @@
+{
+    "experimentalComplexExpressions": true,
+    "apiVersion": 59
+}
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/expected.js b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/expected.js
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/metadata.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/metadata.json
new file mode 100644
index 0000000000..086ed12b46
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-attribute/metadata.json
@@ -0,0 +1,15 @@
+{
+    "warnings": [
+        {
+            "code": 1209,
+            "message": "Invalid expression {classNames[0]} - LWC1209: Template expression doesn't allow computed property access. The current component API version (59) is insufficient and must be increased to at least 66 for this type of expression.",
+            "level": 1,
+            "location": {
+                "line": 3,
+                "column": 12,
+                "start": 36,
+                "length": 23
+            }
+        }
+    ]
+}
\ No newline at end of file
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/actual.html b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/actual.html
new file mode 100644
index 0000000000..38c09182be
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/actual.html
@@ -0,0 +1,3 @@
+<template>
+    {val[state.foo]}
+</template>
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/ast.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/ast.json
new file mode 100644
index 0000000000..9e26dfeeb6
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/ast.json
@@ -0,0 +1 @@
+{}
\ No newline at end of file
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/config.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/config.json
new file mode 100644
index 0000000000..00f1c239e3
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/config.json
@@ -0,0 +1,4 @@
+{
+    "experimentalComplexExpressions": true,
+    "apiVersion": 59
+}
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/expected.js b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/expected.js
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/metadata.json b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/metadata.json
new file mode 100644
index 0000000000..d8d1f798f3
--- /dev/null
+++ b/packages/@lwc/template-compiler/src/__tests__/fixtures/expression-complex/invalid/invalid-api-version-computed-prop-node/metadata.json
@@ -0,0 +1,15 @@
+{
+    "warnings": [
+        {
+            "code": 1209,
+            "message": "Invalid expression {val[state.foo]} - LWC1209: Template expression doesn't allow computed property access. The current component API version (59) is insufficient and must be increased to at least 66 for this type of expression.",
+            "level": 1,
+            "location": {
+                "line": 1,
+                "column": 11,
+                "start": 10,
+                "length": 22
+            }
+        }
+    ]
+}
\ No newline at end of file
diff --git a/packages/@lwc/template-compiler/src/parser/attribute.ts b/packages/@lwc/template-compiler/src/parser/attribute.ts
index a71e261b76..6736a20406 100644
--- a/packages/@lwc/template-compiler/src/parser/attribute.ts
+++ b/packages/@lwc/template-compiler/src/parser/attribute.ts
@@ -24,7 +24,7 @@ import {
     isExpression,
     isPotentialExpression,
 } from './expression';
-import { isComplexTemplateExpressionEnabled } from './expression-complex';
+
 import {
     ATTR_NAME,
     DATA_RE,
@@ -111,7 +111,9 @@ export function normalizeAttributeValue(
     const isQuoted = isQuotedAttribute(rawAttrVal);
     const isEscaped = isEscapedAttribute(rawAttrVal);
     if (!isEscaped && isExpression(value)) {
-        if (isQuoted && !isComplexTemplateExpressionEnabled(ctx)) {
+        // Don't test for the API version here, just check if CTE is enabled.
+        // We can provide more specific errors WRT API versions after the expression has been parsed and we know what it is.
+        if (isQuoted && !ctx.config.experimentalComplexExpressions) {
             // <input value="{myValue}" />
             // -> ambiguity if the attribute value is a template identifier or a string literal.
 
diff --git a/packages/@lwc/template-compiler/src/parser/expression.ts b/packages/@lwc/template-compiler/src/parser/expression.ts
index 9d68abe7be..9313965f3c 100644
--- a/packages/@lwc/template-compiler/src/parser/expression.ts
+++ b/packages/@lwc/template-compiler/src/parser/expression.ts
@@ -7,12 +7,13 @@
 import { parseExpressionAt, isIdentifierStart, isIdentifierChar } from 'acorn';
 import { ParserDiagnostics, invariant } from '@lwc/errors';
 
+import { APIFeature, minApiVersion } from '@lwc/shared';
 import * as t from '../shared/estree';
 import { isReservedES6Keyword } from './utils/javascript';
+import { isComplexTemplateExpressionEnabled } from './expression-complex';
 import type { Expression, Identifier, SourceLocation } from '../shared/types';
 
 import type ParserCtx from './parser';
-import type { NormalizedConfig } from '../config';
 import type { Node } from 'acorn';
 
 export const EXPRESSION_SYMBOL_START = '{';
@@ -30,40 +31,71 @@ export function isPotentialExpression(source: string): boolean {
     return !!source.match(POTENTIAL_EXPRESSION_RE);
 }
 
+const minCteApiVersion = minApiVersion(APIFeature.ENABLE_COMPLEX_TEMPLATE_EXPRESSIONS);
+
 function validateExpression(
     source: string,
     node: t.BaseNode,
-    config: NormalizedConfig
+    ctx: ParserCtx,
+    unquotedAttributeExpression: boolean
 ): asserts node is Expression {
-    const isValidNode = t.isIdentifier(node) || t.isMemberExpression(node);
-    // INVALID_XYZ_COMPLEX provides additional context to the user if CTE is enabled.
-    // The author may not have delimited the CTE with quotes, resulting in it being parsed
-    // as a legacy expression.
-    invariant(
-        isValidNode,
-        config.experimentalComplexExpressions
-            ? ParserDiagnostics.INVALID_NODE_COMPLEX
-            : ParserDiagnostics.INVALID_NODE,
-        [node.type, source]
-    );
-
-    if (t.isMemberExpression(node)) {
+    const cteOnlyNode = !t.isIdentifier(node) && !t.isMemberExpression(node);
+
+    // If this node is not an identifier or a member expression (the only two nodes allowed if complexTemplateExpressions are disabled),
+    // then we throw if the following invariants do not hold true.
+    if (cteOnlyNode) {
+        // complexTemplateExpressions must be enabled if this is a cteOnlyNode.
+        invariant(ctx.config.experimentalComplexExpressions, ParserDiagnostics.INVALID_NODE, [
+            node.type,
+        ]);
+        // complexTemplateExpressions must be enabled and the component API version must be sufficient.
         invariant(
-            config.experimentalComputedMemberExpression || !node.computed,
-            config.experimentalComplexExpressions
-                ? ParserDiagnostics.COMPUTED_PROPERTY_ACCESS_NOT_ALLOWED_COMPLEX
-                : ParserDiagnostics.COMPUTED_PROPERTY_ACCESS_NOT_ALLOWED,
-            [source]
+            isComplexTemplateExpressionEnabled(ctx),
+            ParserDiagnostics.INVALID_NODE_CTE_API_VERSION,
+            [node.type, ctx.apiVersion, minCteApiVersion]
         );
+        // complexTemplateExpressions must be enabled, the component API version must be sufficient and the expression should not be
+        // an unquoted attribute expression.
+        invariant(
+            isComplexTemplateExpressionEnabled(ctx) && !unquotedAttributeExpression,
+            ParserDiagnostics.INVALID_NODE_CTE_UNQUOTED,
+            [node.type, source]
+        );
+    }
+
+    if (t.isMemberExpression(node)) {
+        // If this is a computed node and experimentalComputedMemberExpressions is not enabled,
+        // then we throw if the following invariants do not hold true.
+        if (!ctx.config.experimentalComputedMemberExpression && node.computed) {
+            // complexTemplateExpressions must be enabled.
+            invariant(
+                ctx.config.experimentalComplexExpressions,
+                ParserDiagnostics.COMPUTED_PROPERTY_ACCESS_NOT_ALLOWED,
+                [source]
+            );
+            // complexTemplateExpressions must be enabled and the component API version must be sufficient.
+            invariant(
+                isComplexTemplateExpressionEnabled(ctx),
+                ParserDiagnostics.COMPUTED_PROPERTY_ACCESS_NOT_ALLOWED_CTE_API_VERSION,
+                [source, ctx.apiVersion, minCteApiVersion]
+            );
+            // complexTemplateExpressions must be enabled, the component API version must be sufficient and the expression
+            // should not be an unquoted attribute expression.
+            invariant(
+                isComplexTemplateExpressionEnabled(ctx) && !unquotedAttributeExpression,
+                ParserDiagnostics.COMPUTED_PROPERTY_ACCESS_NOT_ALLOWED_CTE_UNQUOTED,
+                [source]
+            );
+        }
 
         const { object, property } = node;
 
         if (!t.isIdentifier(object)) {
-            validateExpression(source, object, config);
+            validateExpression(source, object, ctx, unquotedAttributeExpression);
         }
 
         if (!t.isIdentifier(property)) {
-            validateExpression(source, property, config);
+            validateExpression(source, property, ctx, unquotedAttributeExpression);
         }
     }
 }
@@ -109,7 +141,8 @@ export function validateSourceIsParsedExpression(source: string, parsedExpressio
 export function parseExpression(
     ctx: ParserCtx,
     source: string,
-    location: SourceLocation
+    location: SourceLocation,
+    unquotedAttributeExpression: boolean
 ): Expression {
     const { ecmaVersion } = ctx;
     return ctx.withErrorWrapping(
@@ -122,7 +155,7 @@ export function parseExpression(
             });
 
             validateSourceIsParsedExpression(source, parsed);
-            validateExpression(source, parsed, ctx.config);
+            validateExpression(source, parsed, ctx, unquotedAttributeExpression);
 
             return { ...parsed, location };
         },
diff --git a/packages/@lwc/template-compiler/src/parser/index.ts b/packages/@lwc/template-compiler/src/parser/index.ts
index 8779a79586..eaa268eed4 100644
--- a/packages/@lwc/template-compiler/src/parser/index.ts
+++ b/packages/@lwc/template-compiler/src/parser/index.ts
@@ -61,7 +61,7 @@ import {
     SUPPORTED_SVG_TAGS,
     VALID_IF_MODIFIER,
 } from './constants';
-import { parseComplexExpression } from './expression-complex';
+import { isComplexTemplateExpressionEnabled, parseComplexExpression } from './expression-complex';
 import type {
     TemplateParseResult,
     Attribute,
@@ -480,7 +480,7 @@ function parseText(
 
         let value: Expression | Literal;
         if (isExpression(token)) {
-            value = parseExpression(ctx, token, sourceLocation);
+            value = parseExpression(ctx, token, sourceLocation, false);
         } else {
             value = ast.literal(decodeTextContent(token));
         }
@@ -562,7 +562,7 @@ function parseTextNode(ctx: ParserCtx, parse5Text: parse5Tools.TextNode): Text[]
 
     const sourceLocation = ast.sourceLocation(location);
 
-    return ctx.config.experimentalComplexExpressions
+    return isComplexTemplateExpressionEnabled(ctx)
         ? parseTextComplex(ctx, rawText, sourceLocation, location)
         : parseText(ctx, rawText, sourceLocation, location);
 }
@@ -1927,12 +1927,12 @@ function getTemplateAttribute(
     */
     const isPotentialComplexExpression =
         quotedExpression && !escapedExpression && value.startsWith(EXPRESSION_SYMBOL_START);
-    if (ctx.config.experimentalComplexExpressions && isPotentialComplexExpression) {
+    if (isComplexTemplateExpressionEnabled(ctx) && isPotentialComplexExpression) {
         const attributeNameOffset = attribute.name.length + 2; // The +2 accounts for the '="' in the attribute: attr="...
         const templateSource = ctx.getSource(attributeLocation.startOffset + attributeNameOffset);
         attrValue = parseComplexExpression(ctx, value, templateSource, location).expression;
     } else if (isExpression(value) && !escapedExpression) {
-        attrValue = parseExpression(ctx, value, location);
+        attrValue = parseExpression(ctx, value, location, !quotedExpression);
     } else if (isBooleanAttribute) {
         attrValue = ast.literal(true);
     } else {

From 411b599b59cb9349443a6a40f701694c94fd64c7 Mon Sep 17 00:00:00 2001
From: John Hefferman <jhefferman@salesforce.com>
Date: Mon, 29 Sep 2025 09:31:42 -0600
Subject: [PATCH 09/11] fix: bundlesize

---
 scripts/bundlesize/bundlesize.config.json | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/bundlesize/bundlesize.config.json b/scripts/bundlesize/bundlesize.config.json
index 57c8efea07..085eddc8d4 100644
--- a/scripts/bundlesize/bundlesize.config.json
+++ b/scripts/bundlesize/bundlesize.config.json
@@ -2,7 +2,7 @@
     "files": [
         {
             "path": "packages/@lwc/engine-dom/dist/index.js",
-            "maxSize": "24.72KB"
+            "maxSize": "24.79KB"
         },
         {
             "path": "packages/@lwc/synthetic-shadow/dist/index.js",

From 70e89713ec0ce8d91d674912831b076941f5a4da Mon Sep 17 00:00:00 2001
From: John Hefferman <jhefferman@salesforce.com>
Date: Mon, 29 Sep 2025 10:48:27 -0600
Subject: [PATCH 10/11] fix: retain original switch logic

---
 packages/@lwc/shared/src/api-version.ts | 35 ++++++++++++++-----------
 1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/packages/@lwc/shared/src/api-version.ts b/packages/@lwc/shared/src/api-version.ts
index becdd472cc..bb5ef0b881 100644
--- a/packages/@lwc/shared/src/api-version.ts
+++ b/packages/@lwc/shared/src/api-version.ts
@@ -123,26 +123,29 @@ export const enum APIFeature {
     ENABLE_COMPLEX_TEMPLATE_EXPRESSIONS,
 }
 
-const minFeatureApiVersions = new Map([
-    [APIFeature.LOWERCASE_SCOPE_TOKENS, APIVersion.V59_246_WINTER_24],
-    [APIFeature.TREAT_ALL_PARSE5_ERRORS_AS_ERRORS, APIVersion.V59_246_WINTER_24],
-    [APIFeature.DISABLE_OBJECT_REST_SPREAD_TRANSFORMATION, APIVersion.V60_248_SPRING_24],
-    [APIFeature.SKIP_UNNECESSARY_REGISTER_DECORATORS, APIVersion.V60_248_SPRING_24],
-    [APIFeature.USE_COMMENTS_FOR_FRAGMENT_BOOKENDS, APIVersion.V60_248_SPRING_24],
-    [APIFeature.USE_FRAGMENTS_FOR_LIGHT_DOM_SLOTS, APIVersion.V60_248_SPRING_24],
-    [APIFeature.ENABLE_ELEMENT_INTERNALS_AND_FACE, APIVersion.V61_250_SUMMER_24],
-    [APIFeature.USE_LIGHT_DOM_SLOT_FORWARDING, APIVersion.V61_250_SUMMER_24],
-    [APIFeature.ENABLE_THIS_DOT_HOST_ELEMENT, APIVersion.V62_252_WINTER_25],
-    [APIFeature.ENABLE_THIS_DOT_STYLE, APIVersion.V62_252_WINTER_25],
-    [APIFeature.TEMPLATE_CLASS_NAME_OBJECT_BINDING, APIVersion.V62_252_WINTER_25],
-    [APIFeature.ENABLE_COMPLEX_TEMPLATE_EXPRESSIONS, APIVersion.V66_260_SPRING_26],
-]);
-
 /**
  * @param apiVersionFeature
  */
 export function minApiVersion(apiVersionFeature: APIFeature): APIVersion {
-    return minFeatureApiVersions.get(apiVersionFeature) || HIGHEST_API_VERSION;
+    switch (apiVersionFeature) {
+        case APIFeature.LOWERCASE_SCOPE_TOKENS:
+        case APIFeature.TREAT_ALL_PARSE5_ERRORS_AS_ERRORS:
+            return APIVersion.V59_246_WINTER_24;
+        case APIFeature.DISABLE_OBJECT_REST_SPREAD_TRANSFORMATION:
+        case APIFeature.SKIP_UNNECESSARY_REGISTER_DECORATORS:
+        case APIFeature.USE_COMMENTS_FOR_FRAGMENT_BOOKENDS:
+        case APIFeature.USE_FRAGMENTS_FOR_LIGHT_DOM_SLOTS:
+            return APIVersion.V60_248_SPRING_24;
+        case APIFeature.ENABLE_ELEMENT_INTERNALS_AND_FACE:
+        case APIFeature.USE_LIGHT_DOM_SLOT_FORWARDING:
+            return APIVersion.V61_250_SUMMER_24;
+        case APIFeature.ENABLE_THIS_DOT_HOST_ELEMENT:
+        case APIFeature.ENABLE_THIS_DOT_STYLE:
+        case APIFeature.TEMPLATE_CLASS_NAME_OBJECT_BINDING:
+            return APIVersion.V62_252_WINTER_25;
+        case APIFeature.ENABLE_COMPLEX_TEMPLATE_EXPRESSIONS:
+            return APIVersion.V66_260_SPRING_26;
+    }
 }
 
 /**

From c0cb49d708ba23855187890665910e00ed65c4fb Mon Sep 17 00:00:00 2001
From: John Hefferman <jhefferman@salesforce.com>
Date: Mon, 29 Sep 2025 13:00:36 -0600
Subject: [PATCH 11/11] fix: review comments

---
 packages/@lwc/template-compiler/src/parser/attribute.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/@lwc/template-compiler/src/parser/attribute.ts b/packages/@lwc/template-compiler/src/parser/attribute.ts
index 6736a20406..ea94e97e05 100644
--- a/packages/@lwc/template-compiler/src/parser/attribute.ts
+++ b/packages/@lwc/template-compiler/src/parser/attribute.ts
@@ -112,7 +112,7 @@ export function normalizeAttributeValue(
     const isEscaped = isEscapedAttribute(rawAttrVal);
     if (!isEscaped && isExpression(value)) {
         // Don't test for the API version here, just check if CTE is enabled.
-        // We can provide more specific errors WRT API versions after the expression has been parsed and we know what it is.
+        // We can provide more specific errors w.r.t API versions after the expression has been parsed and we know what it is.
         if (isQuoted && !ctx.config.experimentalComplexExpressions) {
             // <input value="{myValue}" />
             // -> ambiguity if the attribute value is a template identifier or a string literal.