fix(language-service): Fix crash when no script files are found (#20550)

Fixes the crash in typescript host when getScriptFileNames() returns an
empty array.

PR Close #19325

PR Close #20550

packages/language-service/src/typescript_host.ts

@@ -147,12 +147,20 @@ export class TypeScriptServiceHost implements LanguageServiceHost {
   private ensureAnalyzedModules(): NgAnalyzedModules {
     let analyzedModules = this.analyzedModules;
     if (!analyzedModules) {
+      if (this.host.getScriptFileNames().length === 0) {
+        analyzedModules = {
+          files: [],
+          ngModuleByPipeOrDirective: new Map(),
+          ngModules: [],
+        };
+      } else {
         const analyzeHost = {isSourceFile(filePath: string) { return true; }};
         const programFiles = this.program.getSourceFiles().map(sf => sf.fileName);
-
-      analyzedModules = this.analyzedModules =
+        analyzedModules =
             analyzeNgModules(programFiles, analyzeHost, this.staticSymbolResolver, this.resolver);
       }
+      this.analyzedModules = analyzedModules;
+    }
     return analyzedModules;
   }
 
@@ -358,7 +366,11 @@ export class TypeScriptServiceHost implements LanguageServiceHost {
     if (!result) {
       if (!this.context) {
         // Make up a context by finding the first script and using that as the base dir.
-        this.context = this.host.getScriptFileNames()[0];
+        const scriptFileNames = this.host.getScriptFileNames();
+        if (0 === scriptFileNames.length) {
+          throw new Error('Internal error: no script file names found');
+        }
+        this.context = scriptFileNames[0];
       }
 
       // Use the file context's directory as the base directory.

packages/language-service/test/typescript_host_spec.ts

@@ -39,4 +39,11 @@ describe('completions', () => {
     ngHost = new TypeScriptServiceHost(host, service);
     expect(ngHost.getAnalyzedModules()).toBeDefined();
   });
+
+  it('should not throw if there is no script names', () => {
+    host = new MockTypescriptHost([], toh);
+    service = ts.createLanguageService(host);
+    ngHost = new TypeScriptServiceHost(host, service);
+    expect(() => ngHost.getAnalyzedModules()).not.toThrow();
+  });
 });