v6.0.9: false-positive "v10 installation layout" warning when self-updating from bootstrap 11.7.0 (still reproduces with pnpm 11.19.0)

Summary

pnpm/action-setup@v6.0.9 (0ebf471) still emits a false-positive v10 layout warning whenever it self-updates from the action's bootstrap pnpm (11.7.0) to the project's packageManager pin.

This is the same report as #278 (closed as completed on 2026-07-17 with no comments and no release after v6.0.9). Re-opening as a new issue because the warning is still present when targeting pnpm 11.19.0.

Running self-installer...
    added 1 package in 3s
    Checking for updates...
    Switching pnpm from v11.7.0 to v11.19.0...
    [WARN] Detected a pnpm v10 installation layout at PNPM_HOME. The pnpm shims at PNPM_HOME have been refreshed so the new version is active, but pnpm v11 expects bins in PNPM_HOME/bin. Run "pnpm setup" to migrate your PATH to the v11 layout.
    Successfully updated pnpm to v11.19.0

No real v10 install is involved. The warning is noise in CI; the install still succeeds and the correct version is active.

Reproduction

package.json:

{ "packageManager": "pnpm@11.19.0" }

jobs:
  repro:
    runs-on: ubuntu-latest # also seen on self-hosted linux/arm64
    steps:
      - uses: actions/checkout@v6
      - uses: pnpm/action-setup@0ebf47130e4866e96fce0953f49152a61190b271 # v6.0.9
        # version omitted → reads package.json#packageManager
      - uses: actions/setup-node@v6
        with:
          node-version: 24

Why it fires

The warning string is emitted by pnpm itself during self-update:

https://github.com/pnpm/pnpm/blob/main/pnpm11/engine/pm/commands/src/self-updater/selfUpdate.ts

// pnpm v10 setup linked bins directly into pnpmHomeDir ...
if (hasLegacyHomeDirShim(opts.pnpmHomeDir)) {
  // refresh legacy shims...
  globalWarn(
    'Detected a pnpm v10 installation layout at PNPM_HOME. ...'
  )
}

hasLegacyHomeDirShim treats a pnpm file directly under PNPM_HOME as a v10 marker. In this action, PNPM_HOME is pointed at the bootstrap's node_modules/.bin (see src/install-pnpm/run.ts in v6.0.9), which always contains a pnpm shim from npm ci / the action's own link step. So every self-update from bootstrap 11.7.0 → any other version false-positives by construction.

Notes

• Pinning packageManager to exactly 11.7.0 makes self-update a no-op and the warning disappears (same observation as #278).
• standalone: true does not avoid it on Linux.
• Related genuine migration issue (different cause): pnpm/pnpm#11528 / pnpm/pnpm#11464.

Possible directions (from #278)

1. Give the bootstrap a dedicated PNPM_HOME (e.g. <dest>/pnpm-home) separate from node_modules/.bin.
2. Or teach pnpm's hasLegacyHomeDirShim to distinguish an npm-managed .bin from a real v10 setup layout.

Environment

• pnpm/action-setup@v6.0.9 (0ebf47130e4866e96fce0953f49152a61190b271)
• bootstrap pnpm 11.7.0 → target pnpm 11.19.0
• Observed in GitHub Actions CI (linux/arm64 self-hosted runners and expected on ubuntu-latest)

Happy to help test a fix.

Start in src/install-pnpm/run.ts and reproduce the workflow with packageManager pinned to pnpm@11.19.0, comparing the bootstrap PNPM_HOME and self-update behavior described in the issue. Evaluate the two proposed directions and verify that self-updating no longer emits the false-positive warning while the target pnpm version remains active.