perf(language-service): keep analyzedModules cache when source files don't change (#32562)

This change will improve performance of language service when working in external templates.

PR Close #32562

packages/language-service/src/typescript_host.ts

@@ -275,12 +275,14 @@ export class TypeScriptServiceHost implements LanguageServiceHost {
 
     // Invalidate file that have changed in the static symbol resolver
     const seen = new Set<string>();
+    let hasChanges = false;
     for (const sourceFile of program.getSourceFiles()) {
       const fileName = sourceFile.fileName;
       seen.add(fileName);
       const version = this.tsLsHost.getScriptVersion(fileName);
       const lastVersion = this.fileVersions.get(fileName);
       if (version !== lastVersion) {
+        hasChanges = true;
         this.fileVersions.set(fileName, version);
         this.staticSymbolResolver.invalidateFile(fileName);
       }
@@ -295,7 +297,7 @@ export class TypeScriptServiceHost implements LanguageServiceHost {
 
     this.lastProgram = program;
 
-    return false;
+    return missing.length === 0 && !hasChanges;
   }
 
   /**

packages/language-service/test/typescript_host_spec.ts

@@ -148,4 +148,14 @@ describe('TypeScriptServiceHost', () => {
     expect(newModules.ngModuleByPipeOrDirective.has(helloComp)).toBe(true);
     expect(newModules.ngModuleByPipeOrDirective.has(appComp)).toBe(false);
   });
+
+  it('should not clear caches when external template changes', () => {
+    const tsLSHost = new MockTypescriptHost(['/app/main.ts'], toh);
+    const tsLS = ts.createLanguageService(tsLSHost);
+    const ngLSHost = new TypeScriptServiceHost(tsLSHost, tsLS);
+    const oldModules = ngLSHost.getAnalyzedModules();
+    tsLSHost.override('/app/test.ng', '<div></div>');
+    const newModules = ngLSHost.getAnalyzedModules();
+    expect(newModules).toBe(oldModules);
+  });
 });