fix(@angular/build): report TypeScript declaration emit diagnostics

packages/angular/build/src/builders/library/tests/behavior/build_spec.ts

@@ -278,5 +278,45 @@ describeLibraryBuilder(executeLibraryBuilder, LIBRARY_BUILDER_INFO, (harness) =>
       expect(dtsContent).toContain('LibComponent');
       expect(dtsContent).toContain('CACHED_BUILD');
     });
+
+    it('should report TypeScript declaration emit diagnostics', async () => {
+      await harness.writeFiles({
+        'projects/lib/src/lib/internal.ts': `
+          interface PrivateData {
+            value: number;
+          }
+
+          export const internalData: PrivateData = { value: 42 };
+        `,
+        'projects/lib/src/lib/feature.ts': `
+          import { internalData } from './internal';
+
+          export const data = internalData;
+        `,
+        'projects/lib/src/public-api.ts': `
+          export * from './lib/feature';
+          export * from './lib/lib.service';
+          export * from './lib/lib.component';
+        `,
+      });
+
+      harness.useTarget('build', {
+        ...BASE_OPTIONS,
+      });
+
+      const { result, logs } = await harness.executeOnce({ outputLogsOnFailure: false });
+      expect(result?.success).toBeFalse();
+      expect(logs).toContain(
+        jasmine.objectContaining({
+          level: 'error',
+          message: jasmine.stringMatching(/TS4023:.*PrivateData/),
+        }),
+      );
+      expect(logs).not.toContain(
+        jasmine.objectContaining({
+          message: jasmine.stringContaining('UNRESOLVED_IMPORT'),
+        }),
+      );
+    });
   });
 });

packages/angular/build/src/builders/library/tests/behavior/watch_spec.ts

@@ -905,5 +905,84 @@ describeLibraryBuilder(executeLibraryBuilder, LIBRARY_BUILDER_INFO, (harness) =>
         },
       ]);
     });
+
+    it('should preserve and recover from TypeScript declaration emit diagnostics in watch mode', async () => {
+      await harness.writeFiles({
+        'projects/lib/src/lib/internal.ts': `
+          interface PrivateData {
+            value: number;
+          }
+
+          export const internalData: PrivateData = { value: 42 };
+        `,
+        'projects/lib/src/lib/feature.ts': `
+          import { internalData } from './internal';
+
+          export const data = internalData;
+        `,
+        'projects/lib/src/public-api.ts': `
+          export * from './lib/feature';
+          export * from './lib/lib.service';
+          export * from './lib/lib.component';
+        `,
+      });
+
+      harness.useTarget('build', {
+        ...BASE_OPTIONS,
+        watch: true,
+      });
+
+      await harness.executeWithCases(
+        [
+          async ({ result, logs }) => {
+            expect(result?.success).toBeFalse();
+            expect(logs).toContain(
+              jasmine.objectContaining({
+                level: 'error',
+                message: jasmine.stringMatching(/TS4023:.*PrivateData/),
+              }),
+            );
+
+            // Modify an unrelated file so feature.ts is not re-emitted
+            await harness.writeFile(
+              'projects/lib/src/lib/lib.service.ts',
+              `
+              import { Injectable } from '@angular/core';
+
+              @Injectable({ providedIn: 'root' })
+              export class LibService {
+                updated = true;
+              }
+              `,
+            );
+          },
+          async ({ result, logs }) => {
+            expect(result?.success).toBeFalse();
+            expect(logs).toContain(
+              jasmine.objectContaining({
+                level: 'error',
+                message: jasmine.stringMatching(/TS4023:.*PrivateData/),
+              }),
+            );
+
+            // Fix the declaration error in feature.ts by adding an explicit type annotation
+            await harness.writeFile(
+              'projects/lib/src/lib/feature.ts',
+              `
+              import { internalData } from './internal';
+
+              export const data: { value: number } = internalData;
+              `,
+            );
+          },
+          ({ result }) => {
+            expect(result?.success).toBeTrue();
+            const dtsContent = harness.readFile('dist/lib/types/lib.d.ts');
+            expect(dtsContent).toContain('data');
+          },
+        ],
+        { outputLogsOnFailure: false },
+      );
+    });
   });
 });

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

@@ -80,6 +80,7 @@ class AngularCompilationState {
     public readonly webWorkerTransform: ts.TransformerFactory<ts.SourceFile>,
     public readonly useTypeScriptTranspilation: boolean,
     public readonly diagnosticCache = new WeakMap<ts.SourceFile, ts.Diagnostic[]>(),
+    public readonly declarationDiagnostics = new WeakMap<ts.SourceFile, readonly ts.Diagnostic[]>(),
     public readonly filesWithoutDtsSignature = new Set<string>(),
     public readonly useFallbackRootNames = false,
   ) {}
@@ -358,6 +359,7 @@ export class AotCompilation extends TypeScriptCompilation {
       createWorkerTransformer(hostOptions.processWebWorker.bind(hostOptions)),
       useTypeScriptTranspilation,
       this.#state?.diagnosticCache,
+      this.#state?.declarationDiagnostics,
       filesWithoutDtsSignature,
       useFallbackRootNames,
     );
@@ -377,6 +379,7 @@ export class AotCompilation extends TypeScriptCompilation {
     const {
       affectedFiles,
       angularCompiler,
+      declarationDiagnostics,
       diagnosticCache,
       templateDiagnosticsOptimization,
       typeScriptProgram,
@@ -422,11 +425,16 @@ export class AotCompilation extends TypeScriptCompilation {
           true,
         );
 
-        // Declaration files cannot have template diagnostics
+        // Declaration files cannot have template or declaration emit diagnostics
         if (sourceFile.isDeclarationFile) {
           continue;
         }
 
+        const fileDeclarationDiagnostics = declarationDiagnostics.get(sourceFile);
+        if (fileDeclarationDiagnostics) {
+          yield* fileDeclarationDiagnostics;
+        }
+
         // Only request Angular template diagnostics for affected files to avoid
         // overhead of template diagnostics for unchanged files.
         if (affectedFiles.has(sourceFile)) {
@@ -493,6 +501,7 @@ export class AotCompilation extends TypeScriptCompilation {
       affectedFiles,
       angularCompiler,
       compilerHost,
+      declarationDiagnostics,
       typeScriptProgram,
       webWorkerTransform,
       useTypeScriptTranspilation,
@@ -548,15 +557,22 @@ export class AotCompilation extends TypeScriptCompilation {
     // Emit is handled in write file callback when using TypeScript
     if (useTypeScriptTranspilation) {
       // TypeScript will loop until there are no more affected files in the program
-      while (
-        typeScriptProgram.emitNextAffectedFile(
+      while (true) {
+        const affectedEmitResult = typeScriptProgram.emitNextAffectedFile(
           writeFileCallback,
           undefined,
           undefined,
           transformers,
-        )
-      ) {
-        /* empty */
+        );
+        if (!affectedEmitResult) {
+          break;
+        }
+        if ('kind' in affectedEmitResult.affected) {
+          declarationDiagnostics.set(
+            affectedEmitResult.affected,
+            affectedEmitResult.result.diagnostics,
+          );
+        }
       }
     } else if (compilerOptions.tsBuildInfoFile) {
       // Manually get the builder state for the persistent cache
@@ -589,10 +605,18 @@ export class AotCompilation extends TypeScriptCompilation {
       }
 
       if (useTypeScriptTranspilation) {
-        const emitOnly = emittedDtsSourceFiles.has(sourceFile)
-          ? (EmitOnly.Js as unknown as boolean)
-          : undefined;
-        typeScriptProgram.emit(sourceFile, writeFileCallback, undefined, emitOnly, transformers);
+        const hasEmittedDts = emittedDtsSourceFiles.has(sourceFile);
+        const emitOnly = hasEmittedDts ? (EmitOnly.Js as unknown as boolean) : undefined;
+        const emitResult = typeScriptProgram.emit(
+          sourceFile,
+          writeFileCallback,
+          undefined,
+          emitOnly,
+          transformers,
+        );
+        if (!hasEmittedDts) {
+          declarationDiagnostics.set(sourceFile, emitResult.diagnostics);
+        }
         continue;
       }