feat(language-service): [ivy] Parse Angular compiler options (#36922)

Parse Angular compiler options in Angular language service.

In View Engine, only TypeScript compiler options are read, Angular
compiler options are not. With Ivy, there could be different modes of
compilation, most notably how strict the templates should be checked.
This commit makes the behavior of language service consistent with the
Ivy compiler.

PR Close #36922

packages/language-service/ivy/language_service.ts

@@ -6,12 +6,50 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {CompilerOptions, createNgCompilerOptions} from '@angular/compiler-cli';
 import * as ts from 'typescript/lib/tsserverlibrary';
 
 export class LanguageService {
-  constructor(private readonly tsLS: ts.LanguageService) {}
+  private options: CompilerOptions;
+
+  constructor(project: ts.server.Project, private readonly tsLS: ts.LanguageService) {
+    this.options = parseNgCompilerOptions(project);
+    this.watchConfigFile(project);
+  }
 
   getSemanticDiagnostics(fileName: string): ts.Diagnostic[] {
     return [];
   }
+
+  private watchConfigFile(project: ts.server.Project) {
+    // TODO: Check the case when the project is disposed. An InferredProject
+    // could be disposed when a tsconfig.json is added to the workspace,
+    // in which case it becomes a ConfiguredProject (or vice-versa).
+    // We need to make sure that the FileWatcher is closed.
+    if (!(project instanceof ts.server.ConfiguredProject)) {
+      return;
+    }
+    const {host} = project.projectService;
+    host.watchFile(
+        project.getConfigFilePath(), (fileName: string, eventKind: ts.FileWatcherEventKind) => {
+          project.log(`Config file changed: ${fileName}`);
+          if (eventKind === ts.FileWatcherEventKind.Changed) {
+            this.options = parseNgCompilerOptions(project);
+          }
+        });
+  }
+}
+
+export function parseNgCompilerOptions(project: ts.server.Project): CompilerOptions {
+  let config = {};
+  if (project instanceof ts.server.ConfiguredProject) {
+    const configPath = project.getConfigFilePath();
+    const result = ts.readConfigFile(configPath, path => project.readFile(path));
+    if (result.error) {
+      project.error(ts.flattenDiagnosticMessageText(result.error.messageText, '\n'));
+    }
+    config = result.config || config;
+  }
+  const basePath = project.getCurrentDirectory();
+  return createNgCompilerOptions(basePath, config, project.getCompilationSettings());
 }