fix(language-service): Recover from error in analyzing Ng Modules (#37108)

In place of failing to return analyzed Ng Modules when the analyzer
fails, return the previously-analyzed Ng Modules (which may be empty)
and log an error.

Closes https://github.com/angular/vscode-ng-language-service/issues/777

PR Close #37108

packages/language-service/src/typescript_host.ts

@@ -175,8 +175,15 @@ export class TypeScriptServiceHost implements LanguageServiceHost {
       }
     };
     const programFiles = this.program.getSourceFiles().map(sf => sf.fileName);
-    this.analyzedModules =
+
-        analyzeNgModules(programFiles, analyzeHost, this.staticSymbolResolver, this.resolver);
+    try {
+      this.analyzedModules =
+          analyzeNgModules(programFiles, analyzeHost, this.staticSymbolResolver, this.resolver);
+    } catch (e) {
+      // Analyzing modules may throw; in that case, reuse the old modules.
+      this.error(`Analyzing NgModules failed. ${e}`);
+      return this.analyzedModules;
+    }
 
     // update template references and fileToComponent
     const urlResolver = createOfflineCompileUrlResolver();

packages/language-service/test/test_utils.ts

@@ -101,6 +101,7 @@ export class MockTypescriptHost implements ts.LanguageServiceHost {
   private readonly overrideDirectory = new Set<string>();
   private readonly existsCache = new Map<string, boolean>();
   private readonly fileCache = new Map<string, string|undefined>();
+  errors: string[] = [];
 
   constructor(
       private readonly scriptNames: string[],
@@ -398,6 +399,10 @@ export class MockTypescriptHost implements ts.LanguageServiceHost {
     }
     throw new Error(`Failed to find marker '${selector}' in ${fileName}`);
   }
+
+  error(msg: string) {
+    this.errors.push(msg);
+  }
 }
 
 const locationMarker = /\~\{(\w+(-\w+)*)\}/g;

packages/language-service/test/typescript_host_spec.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import * as ngc from '@angular/compiler';
 import * as ts from 'typescript';
 
 import {TypeScriptServiceHost} from '../src/typescript_host';
@@ -216,4 +217,44 @@ describe('TypeScriptServiceHost', () => {
     // But the content should be exactly the same
     expect(newModules).toEqual(oldModules);
   });
+
+  it('should recover from error in analyzing ng modules', () => {
+    // First create a TypescriptHost with empty script names
+    const tsLSHost = new MockTypescriptHost([]);
+    const tsLS = ts.createLanguageService(tsLSHost);
+    const ngLSHost = new TypeScriptServiceHost(tsLSHost, tsLS);
+    const oldModules = ngLSHost.getAnalyzedModules();
+    expect(oldModules.ngModules).toEqual([]);
+    // Now add a script, this would change the program
+    let fileName = '/app/main.ts';
+    let content = `
+    import {CommonModule} from '@angular/common';
+    import {NgModule} from '@angular/core';
+    
+    @NgModule({
+      entryComponents: [CommonModule],
+    })
+    export class AppModule {}
+    `;
+    tsLSHost.addScript(fileName, content);
+
+    // If analyzing modules throws, the old modules should be returned.
+    let newModules = ngLSHost.getAnalyzedModules();
+    expect(newModules.ngModules).toEqual([]);
+    expect(tsLSHost.errors).toEqual([
+      'Analyzing NgModules failed. Error: CommonModule cannot be used as an entry component.'
+    ]);
+
+    content = `
+    import {CommonModule} from '@angular/common';
+    import {NgModule} from '@angular/core';
+    
+    @NgModule({})
+    export class AppModule {}
+    `;
+    tsLSHost.override(fileName, content);
+    // Check that analyzing modules successfully still works.
+    newModules = ngLSHost.getAnalyzedModules();
+    expect(newModules.ngModules.length).toBeGreaterThan(0);
+  });
 });