fix(ssr): avoid reserved keyword collision (#5108)

packages/@lwc/engine-server/src/__tests__/fixtures/reserved-keywords/expected.html

@@ -0,0 +1,7 @@
+<x-cmp>
+  <template shadowrootmode="open">
+    <h1>
+      hello
+    </h1>
+  </template>
+</x-cmp>

packages/@lwc/engine-server/src/__tests__/fixtures/reserved-keywords/index.js

@@ -0,0 +1,3 @@
+export const tagName = 'x-cmp';
+export { default } from 'x/cmp';
+export * from 'x/cmp';

packages/@lwc/engine-server/src/__tests__/fixtures/reserved-keywords/modules/x/cmp/cmp.html

@@ -0,0 +1,3 @@
+<template>
+    <h1>hello</h1>
+</template>

packages/@lwc/engine-server/src/__tests__/fixtures/reserved-keywords/modules/x/cmp/cmp.js

@@ -0,0 +1,23 @@
+import { LightningElement } from 'lwc';
+
+const privateFields = undefined;
+const publicFields = undefined;
+const stylesheetScopeToken = undefined;
+const hasScopedStylesheets = undefined;
+const defaultScopedStylesheets = undefined;
+
+export default class extends LightningElement {
+    connectedCallback() {
+        // just use the variables to avoid them being tree-shaken
+        Object.assign(
+            {},
+            {
+                privateFields,
+                publicFields,
+                stylesheetScopeToken,
+                hasScopedStylesheets,
+                defaultScopedStylesheets,
+            }
+        );
+    }
+}

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

@@ -15,8 +15,9 @@ import type { Program, Statement, IfStatement } from 'estree';
 import type { ComponentMetaState } from './types';
 
 const bGenerateMarkup = esTemplate`
-    const publicFields = new Set(${/*public fields*/ is.arrayExpression});
-    const privateFields = new Set(${/*private fields*/ is.arrayExpression});
+    // These variables may mix with component-authored variables, so should be reasonably unique
+    const __lwcPublicFields__ = new Set(${/*public fields*/ is.arrayExpression});
+    const __lwcPrivateFields__ = new Set(${/*private fields*/ is.arrayExpression});
 
     async function* generateMarkup(
             tagName, 
@@ -38,7 +39,12 @@ const bGenerateMarkup = esTemplate`
         __establishContextfulRelationship(contextfulParent, instance);
         ${/*connect wire*/ is.statement}
 
-        instance[__SYMBOL__SET_INTERNALS](props, attrs, publicFields, privateFields);
+        instance[__SYMBOL__SET_INTERNALS](
+            props,
+            attrs,
+            __lwcPublicFields__,
+            __lwcPrivateFields__,
+        );
         instance.isConnected = true;
         if (instance.connectedCallback) {
             __mutationTracker.enable(instance);