fix(language-service): remove completion for string (#37983)

If the user inputs a string(e.g. `<div [ngClass]="'str~{cursor}'"></div>`), the completion is useless.

PR Close #37983

packages/language-service/src/expressions.ts

@@ -75,7 +75,16 @@ export function getExpressionCompletions(
     visitKeyedWrite(_ast) {},
     visitLiteralArray(_ast) {},
     visitLiteralMap(_ast) {},
-    visitLiteralPrimitive(_ast) {},
+    visitLiteralPrimitive(ast) {
+      // The type `LiteralPrimitive` include the `ERROR`, and it's wrapped as `string`.
+      // packages/compiler/src/template_parser/binding_parser.ts#L308
+      // So exclude the `ERROR` here.
+      if (typeof ast.value === 'string' &&
+          ast.value ===
+              templateInfo.source.slice(ast.sourceSpan.start + 1, ast.sourceSpan.end - 1)) {
+        result = undefined;
+      }
+    },
     visitMethodCall(_ast) {},
     visitPipe(ast) {
       if (position >= ast.exp.span.end &&

packages/language-service/test/completions_spec.ts

@@ -848,6 +848,13 @@ describe('completions', () => {
     const completions = ngLS.getCompletionsAtPosition(TEST_TEMPLATE, marker.start);
     expect(completions).toBeUndefined();
   });
+
+  it('should not provide completions for string', () => {
+    mockHost.override(TEST_TEMPLATE, `<div [ngClass]="'str~{cursor}'"></div>`);
+    const marker = mockHost.getLocationMarkerFor(TEST_TEMPLATE, 'cursor');
+    const completions = ngLS.getCompletionsAtPosition(TEST_TEMPLATE, marker.start);
+    expect(completions).toBeUndefined();
+  });
 });
 
 function expectContain(