fix(@angular/build): enable code splitting for vitest browser tests - #33949
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This pull request removes the disableCodeSplitting option and resolves ESM binding issues in Vitest/Vite SSR runs. It does this by eagerly invoking __esm initializers in chunk/bundle outputs within the Vitest plugin, and by introducing ensureTestFileEsm in the Angular compiler plugin to append export {}; to test spec files lacking export statements so they are treated as ES modules. The feedback suggests making ensureTestFileEsm idempotent by checking if the file already contains import or export statements before appending export {}; to prevent duplicate appends.
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Enables code splitting for Vitest browser tests while keeping it disabled for Node-based tests (JSDOM/Happy-DOM). Vitest's Node-based module loading emulation (vite-node) is not fully spec compliant and lacks live ESM bindings across chunk boundaries, which can cause uninitialized exports and break mocking. In browser tests, however, the real browser adheres to the ECMAScript spec, so code splitting can be safely enabled there.
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Enables code splitting for Vitest browser tests while keeping it disabled for Node-based tests (JSDOM/Happy-DOM).
Vitest's Node-based module loading emulation (
vite-node) is not fully spec compliant and lacks live ESM bindings across chunk boundaries, which can cause uninitialized exports and break mocking. In browser tests, however, the real browser adheres to the ECMAScript spec, so code splitting can be safely enabled there.