fix(ssr): prohibit variable names in customer code from colliding with SSR-internal variables

packages/@lwc/engine-server/src/__tests__/fixtures/prohibited-variable-name/config.json

@@ -0,0 +1,6 @@
+{
+    "ssrFiles": {
+        "error": "error-ssr.txt",
+        "expected": "expected-ssr.html"
+    }
+}

packages/@lwc/engine-server/src/__tests__/fixtures/prohibited-variable-name/error-ssr.txt

@@ -0,0 +1 @@
+LWCTODO: identifier name '__lwcThrowAnError__' cannot start with '__lwc'

packages/@lwc/engine-server/src/__tests__/fixtures/prohibited-variable-name/expected.html

@@ -0,0 +1,4 @@
+<x-dont-do-it-stupid>
+  <template shadowrootmode="open">
+  </template>
+</x-dont-do-it-stupid>

packages/@lwc/engine-server/src/__tests__/fixtures/prohibited-variable-name/index.js

@@ -0,0 +1,3 @@
+export const tagName = 'x-dont-do-it-stupid';
+export { default } from 'x/dontDoItStupid';
+export * from 'x/dontDoItStupid';

packages/@lwc/engine-server/src/__tests__/fixtures/prohibited-variable-name/modules/x/dontDoItStupid/dontDoItStupid.js

@@ -0,0 +1,9 @@
+import { LightningElement } from 'lwc';
+
+export default class TextStatic extends LightningElement {
+    connectedCallback() {
+        // This will throw a compile-time error in SSRv2!
+        const __lwcThrowAnError__ = 'yup';
+        console.log(__lwcThrowAnError__);
+    }
+}

packages/@lwc/ssr-compiler/src/compile-js/generate-markup.ts

@@ -20,7 +20,7 @@ const bGenerateMarkup = esTemplate`
     const __lwcPublicProperties__ = new Set(${/*public properties*/ is.arrayExpression}.concat(__lwcSuperPublicProperties__));
     const __lwcPrivateProperties__ = new Set(${/*private properties*/ is.arrayExpression});
 
-    async function* generateMarkup(
+    ${/* component class */ 0}[__SYMBOL__GENERATE_MARKUP] = async function* generateMarkup(
             tagName, 
             props, 
             attrs, 
@@ -75,7 +75,6 @@ const bGenerateMarkup = esTemplate`
         );
         yield \`</\${tagName}>\`;
     }
-    ${/* component class */ 0}[__SYMBOL__GENERATE_MARKUP] = generateMarkup;
     ${/* component class */ 0}.__lwcPublicProperties__ = __lwcPublicProperties__;
 `<[Statement]>;
 

packages/@lwc/ssr-compiler/src/compile-js/index.ts

@@ -261,6 +261,13 @@ const visitors: Visitors = {
             }
         },
     },
+    Identifier(path, _state) {
+        const { node } = path;
+        if (node?.name.startsWith('__lwc') && node.name.endsWith('__')) {
+            // TODO [#5032]: Harmonize errors thrown in `@lwc/ssr-compiler`
+            throw new Error(`LWCTODO: identifier name '${node.name}' cannot start with '__lwc'`);
+        }
+    },
 };
 
 function validateUniqueDecorator(decorators: EsDecorator[]) {