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fix(@angular/build): disable code splitting for unit test builds #33729

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dgp1130 merged 1 commit into angular:main from jonmarozick:fix/unit-test-shared-chunk-init

Aug 13, 2026

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fix(@angular/build): disable code splitting for unit test builds #33729

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fix(@angular/build): disable code splitting for unit test builds

jonmarozick Aug 2, 2026

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16 changes: 16 additions & 0 deletions 16 packages/angular/build/src/builders/application/options.ts

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -126,6 +126,20 @@ interface InternalOptions {
		* Suppress build summary and stats table.
		*/
		quiet?: boolean;

		/**
		* Disables esbuild code splitting for the browser code bundle.
		*
		* Splitting emits shared chunks whose exports are read across chunk boundaries as live ESM
		* bindings. A module hoisted into a shared chunk is wrapped in a lazy initializer, so its exported
		* value is only assigned once that initializer runs. Runners that load the generated output
		* through a module runner rather than the browser's own ESM implementation do not reliably
		* preserve those bindings, and an importing chunk can observe the export as `undefined`.
		*
		* Test bundles are never downloaded by a browser, so there is nothing for splitting to optimize
		* there. Used exclusively for tests and shouldn't be used for other kinds of builds.
		*/
		disableCodeSplitting?: boolean;
		}

		/** Full set of options for `application` builder. */
Expand Down Expand Up		@@ -439,6 +453,7 @@ export async function normalizeOptions(
		partialSSRBuild = false,
		externalRuntimeStyles,
		instrumentForCoverage,
		disableCodeSplitting,
		} = options;

		// Return all the normalized options
Expand Down Expand Up		@@ -475,6 +490,7 @@ export async function normalizeOptions(
		watch,
		workspaceRoot,
		entryPoints,
		disableCodeSplitting,
		optimizationOptions,
		outputOptions,
		outExtension,
Expand Down

6 changes: 6 additions & 0 deletions 6 packages/angular/build/src/builders/unit-test/runners/vitest/build-options.ts

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -257,6 +257,12 @@ export async function getVitestBuildOptions(
		outputHashing: adjustOutputHashing(baseBuildOptions.outputHashing),
		optimization: false,
		entryPoints,
		// Every spec file is its own entry point, so splitting hoists any module shared between two
		// specs into a chunk whose exports are then read across a chunk boundary. Those reads rely on
		// live ESM bindings, and a module placed in a shared chunk is only assigned its exported value
		// when that chunk's lazy initializer runs, so an importing chunk can read `undefined`. Nothing
		// downloads these bundles, so there is no benefit to weigh against that.
		disableCodeSplitting: true,
		// Enable support for vitest browser prebundling. Excludes can be controlled with a runnerConfig
		// and the `optimizeDeps.exclude` option.
		externalPackages: true,
Expand Down

172 changes: 172 additions & 0 deletions 172 ...ages/angular/build/src/builders/unit-test/tests/behavior/vitest-shared-chunk-init_spec.ts

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Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,172 @@
		/**
		* @license
		* Copyright Google LLC All Rights Reserved.
		*
		* Use of this source code is governed by an MIT-style license that can be
		* found in the LICENSE file at https://angular.dev/license
		*/

		import { execute } from '../../index';
		import {
		BASE_OPTIONS,
		describeBuilder,
		UNIT_TEST_BUILDER_INFO,
		setupApplicationTarget,
		} from '../setup';

		describeBuilder(execute, UNIT_TEST_BUILDER_INFO, (harness) => {
		describe('Behavior: "Vitest shared chunk initialization"', () => {
		// Regression test for https://github.com/angular/angular-cli/issues/33728.
		//
		// Without `disableCodeSplitting`, esbuild hoists a module imported by more than one spec
		// entry point into a shared chunk behind a lazy `__esm` initializer, and a class-field
		// initializer in another chunk reads the exported value as `undefined` under the jsdom
		// runner. All four trigger conditions are required and encoded below:
		// 1. two spec entry points import the shared module (so it lands in a shared chunk);
		// 2. a component in one entry reads the export during class-field initialization;
		// 3. that component's spec file contains an `async` test callback (no `await` needed);
		// 4. zone.js is in the polyfills (the `setupApplicationTarget` default), which downlevels
		// async and makes esbuild emit the spec entry CommonJS-wrapped.
		//
		// NOTE: the failure this guards against is sensitive to inert content — adding a top-level
		// side effect (even a `console.log`) to the shared or importing module below defused it
		// during reduction. Mirror https://github.com/jonmarozick/ng-shared-chunk-repro when
		// modifying these fixtures.
		it('should provide shared-module exports to class-field initializers in async specs', async () => {
		setupApplicationTarget(harness);

		harness.useTarget('test', {
		...BASE_OPTIONS,
		});

		// Keep the default project's spec deterministic; a third spec entry that does not touch
		// the shared module does not affect the reproduction (verified in a fresh workspace).
		await harness.writeFile(
		'src/app/app.component.spec.ts',
		`
		import { describe, it, expect } from 'vitest';

		describe('AppComponent placeholder', () => {
		it('runs', () => {
		expect(1 + 1).toBe(2);
		});
		});
		`,
		);

		// The shared `const`. Reached from both spec entry points, so it is hoisted into a chunk
		// shared between them.
		await harness.writeFile(
		'src/environments/env-config.ts',
		`
		export interface DealerConfig {
		dealerId: string;
		clientKey: string;
		}

		export const DEALERS: DealerConfig[] = [
		{ dealerId: 'dealer-one', clientKey: 'KEY-ONE' },
		{ dealerId: 'dealer-two', clientKey: 'KEY-TWO' },
		{ dealerId: 'dealer-three', clientKey: 'KEY-THREE' },
		{ dealerId: 'dealer-four', clientKey: 'KEY-FOUR' },
		];
		`,
		);

		// Reached by both spec entries, so it and env-config.ts land in the shared chunk. Reads the
		// const inside a method — after module initialization — and is the passing control.
		await harness.writeFile(
		'src/app/features/lead-generator/services/lead.service.ts',
		`
		import { Injectable } from '@angular/core';

		import { DEALERS } from '../../../../environments/env-config';

		@Injectable({ providedIn: 'root' })
		export class LeadService {
		resolveClientKey(dealerId: string, clientKey?: string): string {
		return clientKey ?? DEALERS.find((d) => d.dealerId === dealerId)?.clientKey ?? '';
		}
		}
		`,
		);

		await harness.writeFile(
		'src/app/features/lead-generator/services/index.ts',
		`export * from './lead.service';\n`,
		);

		// Spec entry point 1 — the second importer that causes the chunk to be shared at all.
		await harness.writeFile(
		'src/app/features/lead-generator/services/lead.service.spec.ts',
		`
		import { describe, it, expect } from 'vitest';
		import { TestBed } from '@angular/core/testing';

		import { LeadService } from './lead.service';

		describe('LeadService', () => {
		it('reads DEALERS inside a method', () => {
		TestBed.configureTestingModule({ providers: [LeadService] });

		expect(TestBed.inject(LeadService).resolveClientKey('dealer-one')).toBe('KEY-ONE');
		});
		});
		`,
		);

		// In the other chunk; reads the shared export eagerly during class-field initialization.
		await harness.writeFile(
		'src/app/features/lead-generator/lead-generator.container.ts',
		`
		import { Component, inject } from '@angular/core';

		import { LeadService } from './services';
		import { DEALERS, DealerConfig } from '../../../environments/env-config';

		@Component({
		selector: 'app-lead-generator',
		standalone: true,
		template: '',
		})
		export class LeadGeneratorContainer {
		private readonly leadService = inject(LeadService);

		readonly dealers: DealerConfig[] = DEALERS;
		readonly dealerOptions = this.dealers.map((d) => d.dealerId);

		hasService(): boolean {
		return this.leadService != null;
		}
		}
		`,
		);

		// Spec entry point 2 — the failing case without the fix. The `async` is load-bearing:
		// zone.js makes the builder downlevel it, the spec then imports the `__async` helper, and
		// esbuild emits this entry CommonJS-wrapped with the component module behind a lazy
		// `__esm` initializer. No `await` is needed; a synchronous callback hides the defect.
		await harness.writeFile(
		'src/app/features/lead-generator/lead-generator.container.spec.ts',
		`
		import { describe, it, expect } from 'vitest';
		import { TestBed } from '@angular/core/testing';

		import { LeadGeneratorContainer } from './lead-generator.container';

		describe('LeadGeneratorContainer', () => {
		it('reads DEALERS in a class-field initialiser', async () => {
		const fixture = TestBed.createComponent(LeadGeneratorContainer);

		expect(fixture.componentInstance.dealers.length).toBe(4);
		});
		});
		`,
		);

		const { result } = await harness.executeOnce();

		expect(result?.success).toBeTrue();
		});
		});
		});

6 changes: 6 additions & 0 deletions 6 packages/angular/build/src/tools/esbuild/application-code-bundle.ts

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -71,6 +71,12 @@ export function createBrowserCodeBundleOptions(
		supported: getFeatureSupport(zoneless),
		};

		if (options.disableCodeSplitting) {
		// Splitting emits shared chunks that are read across chunk boundaries as live ESM bindings,
		// which the unit-test runners' module loading does not reliably preserve.
		buildOptions.splitting = false;
		}

		buildOptions.plugins ??= [];
		buildOptions.plugins.push(
		createWasmPlugin({ allowAsync: zoneless, cache: loadCache }),
Expand Down

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