build: Yarn 4 CI hardening

[erickzhao]

Here are a few follow-up items after #4009.

Building in prepack

As an alternative to #4027, we add the build script to the prepack lifecycle script.

prepack and postpack

Those script are called right at the beginning and the end of each call to yarn pack. They are respectively meant to turn your package from development into production, and cleanup any lingering artifact. For instance, a typical prepack script would call Babel or TypeScript on the source directory to turn .ts files into .js files.

We originally had this under preversion, but that lifecycle script doesn't run anymore after the Yarn 4 upgrade.

Fixing build:watch

The Yarn 4 migration removed the old postbuild script and appended its command to the end of build. build:watch adds the --watch flag to tsc to enable watch mode for the TypeScript build.

We can't just call yarn build --watch anymore due to the added script from postbuild so now build:watch calls the full tsc invocation.

Lockfile fixture hardening

By default, Yarn 4 runs any install in CI with the --immutable flag. This causes problems in our e2e test suite, since we try to yarn install and yarn package within our tests.

The initial Yarn 4 upgrade PR got around this issue by generating lockfile test fixtures for these e2e tests and loading them into the test directory on runtime. However, this trick requires updating these fixtures every time a new release goes out. I tried to do this with the provided update script, but it failed on my machine because it kept generating a Yarn Classic lockfile.

This is because Corepack has global versions of each package manager if the repo doesn't use Corepack. This PR removes the ambiguity by initializing projects with the Yarn 2+ user agent with the correct packageManager entry in package.json.

Note

There are probably a few ways to do this, but being explicit about the package manager version is helpful to have the script run independently of the user's global corepack status.

This also removes some complexity with adding a manual resolution in the same e2e tests (no longer needed due to --immutable installs).

COREPACK_ENABLE_STRICT=0

We were already using COREPACK_ENABLE_STRICT=0 since the Forge repo uses Yarn but we have some tests that run pnpm.

We already had some COREPACK_ENABLE_STRICT workarounds in the tests but this PR disables COREPACK_ENABLE_STRICT for the entirety of the pnpm tests instead of restoring the original value at times.

[erickzhao]

Technically a semver patch or minor change

[MarshallOfSound]

Feels like a fix tbh if it broke before