Stabilizing fsModuleCache

[sheremet-va]

experimental.fsModuleCache

• Introduced in 4.0.11
• Docs
• Rational:
  • In very large projects it takes a long time to transform the whole module graph of a single test file. This can happen when one test file imports from a component with many dependencies. By using a cache, we can reduce this time significantly. Note that Vitest already has a memory cache, so processing the same files is very fast when running multiple test files in parallel.
• Impact:
  • This change mainly affects running a small number of tests in a large repository (350+ modules in a single test file). Running all tests (or maxWorkers number of tests) in parallel has a minimal impact on performance.
• Local benchmark when running a single test file with ~1500 dependencies:

first run

Duration  8.75s (transform 4.02s, setup 629ms, collect 5.52s, tests 2.52s, environment 0ms, prepare 3ms)

vs second run

Duration  5.90s (transform 842ms, setup 543ms, collect 2.35s, tests 2.94s, environment 0ms, prepare 3ms)

Certain files are excluded from caching because transform relies on side effects. By default, files with import.meta.glob are not cached.

Warning

This feature does not affect Browser Mode.