feat(versioning): make parse5 warnings into errors

packages/@lwc/integration-karma/test/static-content/x/staticUnsafeTopLevel/staticUnsafeTopLevel.html

@@ -27,5 +27,4 @@
   <template if:true={doRender}>
     <tr></tr>
   </template>
-  </template>
 </template>

packages/@lwc/shared/src/api-version.ts

@@ -49,11 +49,17 @@ export const enum APIFeature {
      * This is just used as a placeholder.
      */
     DUMMY_FEATURE,
+    /**
+     * If enabled, all parse5 errors will result in a compile-time error, rather than some being treated as warnings
+     * (for backwards compatibility).
+     */
+    TREAT_ALL_PARSE5_ERRORS_AS_ERRORS,
 }
 
 export function isAPIFeatureEnabled(apiVersionFeature: APIFeature, apiVersion: APIVersion) {
     switch (apiVersionFeature) {
         case APIFeature.DUMMY_FEATURE:
+        case APIFeature.TREAT_ALL_PARSE5_ERRORS_AS_ERRORS:
             return apiVersion >= APIVersion.V59_246_WINTER_24;
     }
 }

packages/@lwc/template-compiler/src/__tests__/error-codes.spec.ts

@@ -5,11 +5,14 @@
  * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
  */
 import parse5Errors from 'parse5/lib/common/error-codes';
-import { errorCodesToErrorOn, errorCodesToWarnOn } from '../parser/parse5Errors';
+import { errorCodesToErrorOn, errorCodesToWarnOnInOlderAPIVersions } from '../parser/parse5Errors';
 
 describe('error codes', () => {
     it('all parse5 error codes are accounted for', () => {
-        const allKnownCodes = new Set([...errorCodesToErrorOn, ...errorCodesToWarnOn]);
+        const allKnownCodes = new Set([
+            ...errorCodesToErrorOn,
+            ...errorCodesToWarnOnInOlderAPIVersions,
+        ]);
         for (const code of Object.values(parse5Errors)) {
             expect(allKnownCodes.has(code as string)).toEqual(true);
         }

packages/@lwc/template-compiler/src/__tests__/fixtures/parsing-errors/double-close-template-newer-api-version/actual.html

@@ -0,0 +1,4 @@
+<template>
+    <h1>hello</h1>
+</template>
+</template>

packages/@lwc/template-compiler/src/__tests__/fixtures/parsing-errors/double-close-template-newer-api-version/ast.json

@@ -0,0 +1 @@
+{}

packages/@lwc/template-compiler/src/__tests__/fixtures/parsing-errors/double-close-template-newer-api-version/config.json

@@ -0,0 +1,3 @@
+{
+  "apiVersion": 59
+}

packages/@lwc/template-compiler/src/__tests__/fixtures/parsing-errors/double-close-template-newer-api-version/metadata.json

@@ -0,0 +1,15 @@
+{
+    "warnings": [
+        {
+            "code": 1058,
+            "message": "LWC1058: Invalid HTML syntax: end-tag-without-matching-open-element. For more information, please visit https://html.spec.whatwg.org/multipage/parsing.html#parse-error-end-tag-without-matching-open-element",
+            "level": 1,
+            "location": {
+                "line": 4,
+                "column": 1,
+                "start": 42,
+                "length": 11
+            }
+        }
+    ]
+}

packages/@lwc/template-compiler/src/parser/html.ts

@@ -8,18 +8,23 @@ import * as parse5 from 'parse5';
 import * as he from 'he';
 
 import { ParserDiagnostics } from '@lwc/errors';
-
+import { APIFeature, isAPIFeatureEnabled } from '@lwc/shared';
 import { sourceLocation } from '../shared/ast';
 
 import ParserCtx from './parser';
-import { errorCodesToErrorOn, errorCodesToWarnOn } from './parse5Errors';
+import { errorCodesToErrorOn, errorCodesToWarnOnInOlderAPIVersions } from './parse5Errors';
 
-function getLwcErrorFromParse5Error(code: string) {
+function getLwcErrorFromParse5Error(ctx: ParserCtx, code: string) {
     /* istanbul ignore else */
     if (errorCodesToErrorOn.has(code)) {
         return ParserDiagnostics.INVALID_HTML_SYNTAX;
-    } else if (errorCodesToWarnOn.has(code)) {
-        return ParserDiagnostics.INVALID_HTML_SYNTAX_WARNING;
+    } else if (errorCodesToWarnOnInOlderAPIVersions.has(code)) {
+        // In newer API versions, all parse 5 errors are errors, not warnings
+        if (isAPIFeatureEnabled(APIFeature.TREAT_ALL_PARSE5_ERRORS_AS_ERRORS, ctx.apiVersion)) {
+            return ParserDiagnostics.INVALID_HTML_SYNTAX;
+        } else {
+            return ParserDiagnostics.INVALID_HTML_SYNTAX_WARNING;
+        }
     } else {
         // It should be impossible to reach here; we have a test in parser.spec.ts to ensure
         // all error codes are accounted for. But just to be safe, make it a warning.
@@ -34,7 +39,7 @@ export function parseHTML(ctx: ParserCtx, source: string) {
     const onParseError = (err: parse5.ParsingError) => {
         const { code, ...location } = err;
 
-        const lwcError = getLwcErrorFromParse5Error(code);
+        const lwcError = getLwcErrorFromParse5Error(ctx, code);
         ctx.warnAtLocation(lwcError, sourceLocation(location), [code]);
     };
 

packages/@lwc/template-compiler/src/parser/parse5Errors.ts

@@ -59,7 +59,7 @@ export const errorCodesToErrorOn = new Set([
 ]);
 
 // These were added between parse5-with-errors v4.0.4 and parse5 v6.0.1
-export const errorCodesToWarnOn = new Set([
+export const errorCodesToWarnOnInOlderAPIVersions = new Set([
     'non-conforming-doctype',
     'missing-doctype',
     'misplaced-doctype',

packages/@lwc/template-compiler/src/parser/parser.ts

@@ -13,6 +13,7 @@ import {
     LWCErrorInfo,
     normalizeToDiagnostic,
 } from '@lwc/errors';
+import { APIVersion } from '@lwc/shared';
 import { NormalizedConfig } from '../config';
 import { isPreserveCommentsDirective, isRenderModeDirective } from '../shared/ast';
 
@@ -106,12 +107,14 @@ export default class ParserCtx {
 
     renderMode: LWCDirectiveRenderMode;
     preserveComments: boolean;
+    apiVersion: APIVersion;
 
     constructor(source: String, config: NormalizedConfig) {
         this.source = source;
         this.config = config;
         this.renderMode = LWCDirectiveRenderMode.shadow;
         this.preserveComments = config.preserveHtmlComments;
+        this.apiVersion = config.apiVersion;
     }
 
     getSource(start: number, end: number): string {