yarn install in CI

yarn install installs from yarn.lock; in CI you want it to refuse lockfile changes.

Yarn Classic uses --frozen-lockfile; Yarn Berry (v2+) uses --immutable. Both fail the build if the lockfile would change.

Common flags

• --immutable - Yarn 2+ reproducible install
• --frozen-lockfile - Yarn 1 equivalent
• --immutable-cache - also freeze the cache
• --inline-builds - show build script output

Example in CI

Reproducible install on Yarn Berry.

yarn install --immutable

In CI

A lockfile-would-change failure means dependencies were edited without committing yarn.lock. Cache .yarn/cache for speed.

Key takeaways

• Yarn 2+: --immutable; Yarn 1: --frozen-lockfile.
• It fails if the lockfile would change.
• Cache .yarn/cache between runs.

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