feat: add specific error message for reserved keywords (#5657)

* feat: add specific error message for reserved keywords

* feat: updated the express.ts to do the isReservedES6Keyword only once

Author: yashwanthvanama

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: 1211
+ * Next error code: 1212
  */
 
 export * from './compiler';

packages/@lwc/errors/src/compiler/error-info/template-transform.ts

@@ -1020,4 +1020,11 @@ export const ParserDiagnostics = {
         level: DiagnosticLevel.Error,
         url: '',
     },
+
+    RESERVED_KEYWORD_AS_IDENTIFIER: {
+        code: 1211,
+        message: '{0} is a reserved keyword and cannot be used as an identifier.',
+        level: DiagnosticLevel.Error,
+        url: '',
+    },
 } as const satisfies Record<string, LWCErrorInfo>;

packages/@lwc/template-compiler/src/__tests__/fixtures/expression/reverved-keyword/metadata.json

@@ -13,8 +13,8 @@
             "url": ""
         },
         {
-            "code": 1059,
-            "message": "LWC1059: const is not a valid identifier",
+            "code": 1211,
+            "message": "LWC1211: const is a reserved keyword and cannot be used as an identifier.",
             "level": 1,
             "location": {
                 "line": 3,

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

@@ -177,7 +177,12 @@ export function parseIdentifier(
         isValid = isIdentifierChar(source.charCodeAt(i));
     }
 
-    if (isValid && !isReservedES6Keyword(source)) {
+    if (isValid) {
+        if (isReservedES6Keyword(source)) {
+            ctx.throwAtLocation(ParserDiagnostics.RESERVED_KEYWORD_AS_IDENTIFIER, location, [
+                source,
+            ]);
+        }
         return {
             ...t.identifier(source),
             location,