fix(core): parse incorrect ML open tag as text (#29328)

This PR alligns markup language lexer with the previous behaviour in version 7.x:
https://stackblitz.com/edit/angular-iancj2

While this behaviour is not perfect (we should be giving users an error message
here about invalid HTML instead of assuming text node) this is probably best we
can do without more substential re-write of lexing / parsing infrastructure.

This PR just fixes #29231 and restores VE behaviour - a more elaborate fix will
be done in a separate PR as it requries non-trivial rewrites.

PR Close #29328

packages/compiler/src/ml_parser/lexer.ts

@@ -461,12 +461,14 @@ class _Tokenizer {
     let tagName: string;
     let prefix: string;
     let openTagToken: Token|undefined;
+    let tokensBeforeTagOpen = this.tokens.length;
     const innerStart = this._cursor.clone();
     try {
       if (!chars.isAsciiLetter(this._cursor.peek())) {
         throw this._createError(
             _unexpectedCharacterErrorMsg(this._cursor.peek()), this._cursor.getSpan(start));
       }
+
       openTagToken = this._consumeTagOpenStart(start);
       prefix = openTagToken.parts[0];
       tagName = openTagToken.parts[1];
@@ -483,10 +485,10 @@ class _Tokenizer {
       this._consumeTagOpenEnd();
     } catch (e) {
       if (e instanceof _ControlFlowError) {
-        // When the start tag is invalid, assume we want a "<"
+        // When the start tag is invalid (including invalid "attributes"), assume we want a "<"
         this._cursor = innerStart;
         if (openTagToken) {
-          this.tokens.pop();
+          this.tokens.length = tokensBeforeTagOpen;
         }
         // Back to back text tokens are merged at the end
         this._beginToken(TokenType.TEXT, start);
@@ -528,6 +530,10 @@ class _Tokenizer {
   }
 
   private _consumeAttributeName() {
+    const attrNameStart = this._cursor.peek();
+    if (attrNameStart === chars.$SQ || attrNameStart === chars.$DQ) {
+      throw this._createError(_unexpectedCharacterErrorMsg(attrNameStart), this._cursor.getSpan());
+    }
     this._beginToken(TokenType.ATTR_NAME);
     const prefixAndName = this._consumePrefixAndName();
     this._endToken(prefixAndName);

packages/compiler/test/ml_parser/lexer_spec.ts

@@ -7,7 +7,6 @@
  */
 
 import {getHtmlTagDefinition} from '../../src/ml_parser/html_tags';
-import {InterpolationConfig} from '../../src/ml_parser/interpolation_config';
 import * as lex from '../../src/ml_parser/lexer';
 import {ParseLocation, ParseSourceFile, ParseSourceSpan} from '../../src/parse_util';
 
@@ -378,6 +377,18 @@ import {ParseLocation, ParseSourceFile, ParseSourceSpan} from '../../src/parse_u
         ]);
       });
 
+      it('should report missing closing single quote', () => {
+        expect(tokenizeAndHumanizeErrors('<t a=\'b>')).toEqual([
+          [lex.TokenType.ATTR_VALUE, 'Unexpected character "EOF"', '0:8'],
+        ]);
+      });
+
+      it('should report missing closing double quote', () => {
+        expect(tokenizeAndHumanizeErrors('<t a="b>')).toEqual([
+          [lex.TokenType.ATTR_VALUE, 'Unexpected character "EOF"', '0:8'],
+        ]);
+      });
+
     });
 
     describe('closing tags', () => {
@@ -552,6 +563,31 @@ import {ParseLocation, ParseSourceFile, ParseSourceSpan} from '../../src/parse_u
         ]);
       });
 
+      it('should parse start tags quotes in place of an attribute name as text', () => {
+        expect(tokenizeAndHumanizeParts('<t ">')).toEqual([
+          [lex.TokenType.TEXT, '<t ">'],
+          [lex.TokenType.EOF],
+        ]);
+
+        expect(tokenizeAndHumanizeParts('<t \'>')).toEqual([
+          [lex.TokenType.TEXT, '<t \'>'],
+          [lex.TokenType.EOF],
+        ]);
+      });
+
+      it('should parse start tags quotes in place of an attribute name (after a valid attribute) as text',
+         () => {
+           expect(tokenizeAndHumanizeParts('<t a="b" ">')).toEqual([
+             [lex.TokenType.TEXT, '<t a="b" ">'],
+             [lex.TokenType.EOF],
+           ]);
+
+           expect(tokenizeAndHumanizeParts('<t a=\'b\' \'>')).toEqual([
+             [lex.TokenType.TEXT, '<t a=\'b\' \'>'],
+             [lex.TokenType.EOF],
+           ]);
+         });
+
       it('should be able to escape {', () => {
         expect(tokenizeAndHumanizeParts('{{ "{" }}')).toEqual([
           [lex.TokenType.TEXT, '{{ "{" }}'],