fix(language-service): Should not crash if expr ends unexpectedly (#33524)

If there is any parser errors when parsing template, we should stop
immediately and not proceed with template expression diagnostics.

This regression is caused by 6d11154652
and affected v9.0.0-next.4 onwards.

PR closes https://github.com/angular/vscode-ng-language-service/issues/436

PR Close #33524

packages/language-service/src/diagnostics.ts

@@ -21,26 +21,23 @@ import {findPropertyValueOfType, findTightestNode, offsetSpan, spanOf} from './u
  * @param ast contains HTML and template AST
  */
 export function getTemplateDiagnostics(ast: AstResult): ng.Diagnostic[] {
-  const results: ng.Diagnostic[] = [];
   const {parseErrors, templateAst, htmlAst, template} = ast;
-  if (parseErrors) {
-    results.push(...parseErrors.map(e => {
+  if (parseErrors && parseErrors.length) {
+    return parseErrors.map(e => {
       return {
         kind: ng.DiagnosticKind.Error,
         span: offsetSpan(spanOf(e.span), template.span.start),
         message: e.msg,
       };
-    }));
+    });
   }
-  const expressionDiagnostics = getTemplateExpressionDiagnostics({
+  return getTemplateExpressionDiagnostics({
     templateAst: templateAst,
     htmlAst: htmlAst,
     offset: template.span.start,
     query: template.query,
     members: template.members,
   });
-  results.push(...expressionDiagnostics);
-  return results;
 }
 
 /**

packages/language-service/test/diagnostics_spec.ts

@@ -56,6 +56,19 @@ describe('diagnostics', () => {
     }
   });
 
+  it('should report error for unexpected end of expression', () => {
+    const content = mockHost.override(TEST_TEMPLATE, `{{ 5 / }}`);
+    const diags = ngLS.getDiagnostics(TEST_TEMPLATE);
+    expect(diags.length).toBe(1);
+    const {messageText, start, length} = diags[0];
+    expect(messageText)
+        .toBe(
+            'Parser Error: Unexpected end of expression: {{ 5 / }} ' +
+            'at the end of the expression [{{ 5 / }}] in /app/test.ng@0:0');
+    expect(start).toBe(0);
+    expect(length).toBe(content.length);
+  });
+
   // https://github.com/angular/vscode-ng-language-service/issues/242
   it('should support $any() type cast function', () => {
     mockHost.override(TEST_TEMPLATE, `<div>{{$any(title).xyz}}</div>`);