fix(@angular/build): enforce library compilerOptions and skip unused .tsbuildinfo emit

Ensure library compilations explicitly set `noEmit: false`, `emitDeclarationOnly: false`, and `emitDecoratorMetadata: false` in `transformCompilerOptions` so that configurations extending a root `tsconfig.json` with `noEmit` or `emitDeclarationOnly` still emit both JavaScript and declaration files.

Author: alan-agius4

packages/angular/build/src/tools/angular/compilation/angular-compilation_spec.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
+import path from 'node:path';
 import ts from 'typescript';
 import type { AngularHostOptions } from '../angular-host';
 import { CompilerOptionOverrides, transformCompilerOptions } from './compiler-options';
@@ -476,8 +477,36 @@ describe('AngularCompilation', () => {
       expect(compilerOptions['_useTypeScriptTranspilation']).toBe(true);
       expect(compilerOptions.supportTestBed).toBe(true);
       expect(compilerOptions.supportJitMode).toBe(true);
+      expect(compilerOptions.noEmit).toBe(false);
       expect(compilerOptions.noEmitOnError).toBe(false);
+      expect(compilerOptions.emitDeclarationOnly).toBe(false);
       expect(compilerOptions.composite).toBe(false);
     });
+
+    it('enforces library compiler options and skips app-only target warning', () => {
+      const { compilerOptions, warnings } = transformCompilerOptions(
+        ts,
+        {
+          target: ts.ScriptTarget.ES2020,
+          noEmit: true,
+          emitDeclarationOnly: true,
+          isolatedModules: true,
+        },
+        {
+          cachePath: '/tmp/cache',
+        },
+        'tsconfig.lib.json',
+        'library',
+      );
+
+      expect(compilerOptions.target).toBe(ts.ScriptTarget.ES2022);
+      expect(compilerOptions.module).toBe(ts.ModuleKind.Preserve);
+      expect(compilerOptions.useDefineForClassFields).toBeUndefined();
+      expect(compilerOptions.noEmit).toBe(false);
+      expect(compilerOptions.emitDeclarationOnly).toBe(false);
+      expect(compilerOptions.incremental).toBe(true);
+      expect(compilerOptions.tsBuildInfoFile).toBe(path.join('/tmp/cache', '.tsbuildinfo'));
+      expect(warnings).toEqual([]);
+    });
   });
 });

packages/angular/build/src/tools/angular/compilation/compiler-options.ts

@@ -39,6 +39,17 @@ export function transformCompilerOptions(
   const warnings: PartialMessage[] = [];
   const isLibrary = buildType === 'library';
 
+  if (isLibrary) {
+    compilerOptions.target = typeScript.ScriptTarget.ES2022;
+    compilerOptions.module = typeScript.ModuleKind.Preserve;
+    compilerOptions.importHelpers = true;
+    compilerOptions.declaration = true;
+    compilerOptions.declarationMap = !!(
+      overrides?.declarationMap ?? compilerOptions.declarationMap
+    );
+    compilerOptions.declarationDir = undefined;
+  }
+
   if (
     compilerOptions.target === undefined ||
     compilerOptions.target < typeScript.ScriptTarget.ES2022
@@ -112,18 +123,6 @@ export function transformCompilerOptions(
     });
   }
 
-  if (isLibrary) {
-    compilerOptions.target = typeScript.ScriptTarget.ES2022;
-    compilerOptions.module = typeScript.ModuleKind.ES2022;
-    compilerOptions.moduleResolution = typeScript.ModuleResolutionKind.Bundler;
-    compilerOptions.importHelpers = true;
-    compilerOptions.declaration = true;
-    compilerOptions.declarationMap = !!(
-      overrides?.declarationMap ?? compilerOptions.declarationMap
-    );
-    compilerOptions.declarationDir = undefined;
-  }
-
   // Synchronize custom resolve conditions.
   // Set if using the supported bundler resolution mode (bundler is the default in new projects)
   if (
@@ -137,7 +136,9 @@ export function transformCompilerOptions(
     compilerOptions: {
       ...compilerOptions,
       basePath: overrides?.basePath ? toPosixPath(overrides.basePath) : compilerOptions.basePath,
+      noEmit: false,
       noEmitOnError: false,
+      emitDeclarationOnly: false,
       composite: false,
       inlineSources: !!overrides?.sourcemap,
       inlineSourceMap: !isLibrary && !!overrides?.sourcemap,