From 93fef8b29767a77e025be5be8cf1cfd61bbfa107 Mon Sep 17 00:00:00 2001
From: Alan Agius <17563226+alan-agius4@users.noreply.github.com>
Date: Mon, 12 Oct 2026 13:15:29 +0000
Subject: [PATCH] perf(@angular/build): enable TypeScript incremental build
 cache in library builder

Pass the normalized `cacheOptions.path` to `compilationInstance.initialize` when persistent disk caching is enabled so TypeScript writes and reuses `.tsbuildinfo` across builds.
---
 .../builders/library/pipeline/compilation.ts  |  4 +-
 .../library/tests/behavior/build_spec.ts      | 42 +++++++++++++++++++
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/packages/angular/build/src/builders/library/pipeline/compilation.ts b/packages/angular/build/src/builders/library/pipeline/compilation.ts
index 51a8fb0d231e..a4d26f3457da 100644
--- a/packages/angular/build/src/builders/library/pipeline/compilation.ts
+++ b/packages/angular/build/src/builders/library/pipeline/compilation.ts
@@ -69,7 +69,8 @@ export async function compileLibrary(
   cached?: SingleProgramCache,
   modifiedFiles?: Set<string>,
 ): Promise<LibraryCompilationOutput> {
-  const { tsConfigPath, compilationMode, preserveSymlinks, colors, declarationMap } = options;
+  const { tsConfigPath, compilationMode, preserveSymlinks, colors, declarationMap, cacheOptions } =
+    options;
 
   const entryPathsMap: Record<string, string[]> = {};
   const rootFiles: string[] = [];
@@ -141,6 +142,7 @@ export async function compileLibrary(
         declarationMap,
         compilationMode,
         paths: entryPathsMap,
+        cachePath: cacheOptions.enabled ? cacheOptions.path : undefined,
       },
       'library',
     );
diff --git a/packages/angular/build/src/builders/library/tests/behavior/build_spec.ts b/packages/angular/build/src/builders/library/tests/behavior/build_spec.ts
index e55a414c1ada..8cba60855f2d 100644
--- a/packages/angular/build/src/builders/library/tests/behavior/build_spec.ts
+++ b/packages/angular/build/src/builders/library/tests/behavior/build_spec.ts
@@ -230,5 +230,47 @@ describeLibraryBuilder(executeLibraryBuilder, LIBRARY_BUILDER_INFO, (harness) =>
         }),
       );
     });
+
+    it('should write and reuse .tsbuildinfo in the persistent cache directory when cache is enabled', async () => {
+      harness.useProject('lib', {
+        root: 'projects/lib',
+        sourceRoot: 'projects/lib/src',
+        cli: {
+          cache: {
+            enabled: true,
+            environment: 'all',
+            path: '.angular/cache',
+          },
+        },
+      });
+
+      harness.useTarget('build', {
+        ...BASE_OPTIONS,
+      });
+
+      const firstBuild = await harness.executeOnce();
+      expect(firstBuild.result?.success).toBeTrue();
+      harness
+        .expectFile('.angular/cache/0.0.0-PLACEHOLDER/lib/angular-build-library/.tsbuildinfo')
+        .toExist();
+
+      await harness.writeFile(
+        'projects/lib/src/public-api.ts',
+        `
+          export * from './lib/lib.service';
+          export * from './lib/lib.component';
+          export const CACHED_BUILD = true;
+        `,
+      );
+
+      const secondBuild = await harness.executeOnce();
+      expect(secondBuild.result?.success).toBeTrue();
+      const fesmContent = harness.readFile('dist/lib/fesm2022/lib.mjs');
+      expect(fesmContent).toContain('LibComponent');
+      expect(fesmContent).toContain('CACHED_BUILD');
+      const dtsContent = harness.readFile('dist/lib/types/lib.d.ts');
+      expect(dtsContent).toContain('LibComponent');
+      expect(dtsContent).toContain('CACHED_BUILD');
+    });
   });
 });