test(language-service): do not invalidate @angular/core (#36845)

Fix typo and add test cases for https://github.com/angular/angular/pull/36783

PR closes https://github.com/angular/vscode-ng-language-service/issues/713

PR Close #36845

packages/language-service/src/typescript_host.ts

@@ -220,8 +220,12 @@ export class TypeScriptServiceHost implements LanguageServiceHost {
     const ANGULAR_CORE = '@angular/core';
     const corePath = this.reflectorHost.moduleNameToFileName(ANGULAR_CORE);
     for (const {fileName} of program.getSourceFiles()) {
-      // If the `@angular/core` has been edited, the language service should be restart,
-      // so ignore the change of `@angular/core`.
+      // If `@angular/core` is edited, the language service would have to be
+      // restarted, so ignore changes to `@angular/core`.
+      // When the StaticReflector is initialized at startup, it loads core
+      // symbols from @angular/core by calling initializeConversionMap(). This
+      // is only done once. If the file is invalidated, some of the core symbols
+      // will be lost permanently.
       if (fileName === corePath) {
         continue;
       }

packages/language-service/test/typescript_host_spec.ts

@@ -176,4 +176,43 @@ describe('TypeScriptServiceHost', () => {
     // files have changed.
     expect(newModules).toBe(oldModules);
   });
+
+  it('should not reload @angular/core on changes', () => {
+    const tsLSHost = new MockTypescriptHost(['/app/main.ts']);
+    const tsLS = ts.createLanguageService(tsLSHost);
+    const ngLSHost = new TypeScriptServiceHost(tsLSHost, tsLS);
+    const oldModules = ngLSHost.getAnalyzedModules();
+    const ngCore = '/node_modules/@angular/core/core.d.ts';
+    const originalContent = tsLSHost.readFile(ngCore);
+    const oldVersion = tsLSHost.getScriptVersion(ngCore);
+    tsLSHost.override(ngCore, originalContent + '\n\n');
+    const newVersion = tsLSHost.getScriptVersion(ngCore);
+    expect(newVersion).not.toBe(oldVersion);
+    const newModules = ngLSHost.getAnalyzedModules();
+    // Had @angular/core been invalidated, we'd get a different instance of
+    // analyzed modules, with one module missing - ApplicationModule
+    // The absence of this module will cause language service to stop working.
+    expect(newModules).toBe(oldModules);
+    const ApplicationModule =
+        newModules.ngModules.find(m => m.type.reference.name === 'ApplicationModule');
+    expect(ApplicationModule).toBeDefined();
+  });
+
+  it('should reload @angular/common on changes', () => {
+    const tsLSHost = new MockTypescriptHost(['/app/main.ts']);
+    const tsLS = ts.createLanguageService(tsLSHost);
+    const ngLSHost = new TypeScriptServiceHost(tsLSHost, tsLS);
+    const oldModules = ngLSHost.getAnalyzedModules();
+    const ngCommon = '/node_modules/@angular/common/common.d.ts';
+    const originalContent = tsLSHost.readFile(ngCommon);
+    const oldVersion = tsLSHost.getScriptVersion(ngCommon);
+    tsLSHost.override(ngCommon, originalContent + '\n\n');
+    const newVersion = tsLSHost.getScriptVersion(ngCommon);
+    expect(newVersion).not.toBe(oldVersion);
+    const newModules = ngLSHost.getAnalyzedModules();
+    // We get a new instance of analyzed modules
+    expect(newModules).not.toBe(oldModules);
+    // But the content should be exactly the same
+    expect(newModules).toEqual(oldModules);
+  });
 });