fix(jest): default isolatedModules to true for faster compilation (fixes #1899)#2191
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just-jeb wants to merge 2 commits into
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fix(jest): default isolatedModules to true for faster compilation (fixes #1899)#2191just-jeb wants to merge 2 commits into
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just-jeb
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#1899) Angular 19 introduced signals, new control flow syntax, and standalone-by-default components. These produce significantly more complex TypeScript that causes the ts-jest language service (used when isolatedModules: false) to build a full cross-file Program per test file, resulting in severe slowdowns (reports of 2 min → 15 min test runs). Root cause: when isolatedModules is false (previously the implicit default), ts-jest instantiates a TypeScript LanguageService and rebuilds a full Program for each file. Angular 19+'s richer type surface makes this path prohibitively slow. Fix: set isolatedModules: true in the builder's default transformer options. This switches ts-jest to its fast per-file transpile path, matching the recommendation from jest-preset-angular's own example apps since v14.4.0. Cross-file type checking is better served by tsc --noEmit or ng build. Users who need the previous behaviour can opt out in their jest.config.ts: transform: { '^.+\.(ts|js|mjs|html|svg)$': ['jest-preset-angular', { isolatedModules: false }] } BREAKING CHANGE: isolatedModules now defaults to true. This disables cross-file TypeScript type checking during jest runs. Targeted for the next major version.
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…on test Remove isolatedModules:true assertions from the unit spec — they tested implementation details (object shape), not user-visible behavior. Replace with targeted assertions on tsconfig path resolution, which is the actual behavioral contract of the resolver. Add isolated-modules-default integration test entry that proves Angular component tests still pass end-to-end with isolatedModules:true active, providing the behavioral regression guard for #1899.
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What is the current behavior?
Angular 19 introduced signals, new control flow syntax, and standalone-by-default components. With
isolatedModules: false(today's default),ts-jestbuilds a full cross-file Program per test file, producing severe slowdowns — reports of 2-minute test runs ballooning to 15 minutes after the upgrade.jest-preset-angularhas been recommendingisolatedModules: truesince v14.4.0 and ships it as the default in their A19+ presets.Issue Number: #1899
What is the new behavior?
isolatedModules: trueis set in the default per-project ts-jest transform config. Users can still override via their ownjest.config.{js,ts,...}.Does this PR introduce a breaking change?
isolatedModules: truedisallows certain TS patterns:const enumcannot be inlined across files — must be regularenumor runtime-evaluatedtypemodifier (export type { X }rather thanexport { X }whenXis a type)const enumdeclarations from.d.tsfiles (uncommon) requirepreserveValueImportsThese produce loud TS compile errors at test time, not silent miscompiles. Ships in the next major.
CHANGELOG migration note (draft)
Other information
Branch was force-pushed to drop the unrelated custom-esbuild changes that belonged in PR #2192. Only the jest commit remains.