[Test] Avoid unnecessary package manager install lock

[EscapeB]

Summary

This PR extracts the package-manager install lock optimization from microsoft#5830 into a standalone change.

Rush now skips acquiring the global package manager install lock when the requested package manager is already installed and no matching install lock file exists. If a lock file exists, Rush still acquires the lock to preserve stale/dirty recovery behavior.

Testing

node common/scripts/install-run-rush.js test --to @microsoft/rush-lib --verbose

Summary by CodeRabbit

• Bug Fixes
  • Improved package manager setup to avoid unnecessary global locking and reinstallations when the requested package manager is already available.
  • Ensured installation locks are reliably released, including when installation encounters an error.
  • Preserved required setup steps while safely handling existing installation lock files.

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🧹 Nitpick comments (1)

libraries/rush-lib/src/logic/test/InstallHelpers.test.ts (1)

129-250: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Missing test for the "invalid marker + no lock file" branch.

The two new tests cover marker-valid/no-lock (skip lock) and lock-file-present (acquire lock, dirty). Neither covers marker-invalid + no lock file present, which should still take the lock-acquisition path in InstallHelpers.ts (Line 436). Worth adding to lock down this branch of the new conditional.

🧪 Suggested additional test

it('acquires the global lock when the package manager marker is invalid', async () => {
  const rushGlobalFolder: RushGlobalFolder = getRushGlobalFolder();
  // Do not call writeInstalledPackageManagerAsync, so no valid marker exists.

  const lockAcquireSpy: jest.SpyInstance = jest.spyOn(LockFile, 'acquireAsync').mockResolvedValue({
    dirtyWhenAcquired: false,
    release: jest.fn()
  } as unknown as LockFile);
  const installSpy: jest.SpyInstance = jest
    .spyOn(Utilities, 'installPackageInDirectoryAsync')
    .mockResolvedValue();
  const rushConfiguration: RushConfiguration = getRushConfiguration();

  await InstallHelpers.ensureLocalPackageManagerAsync(rushConfiguration, rushGlobalFolder, 1, true);

  expect(lockAcquireSpy).toHaveBeenCalledTimes(1);
  expect(installSpy).toHaveBeenCalledTimes(1);
});

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@libraries/rush-lib/src/logic/test/InstallHelpers.test.ts` around lines 129 -
250, Add a test in the ensureLocalPackageManagerAsync suite covering an invalid
or missing package-manager marker with no lock file. Do not call
writeInstalledPackageManagerAsync; mock LockFile.acquireAsync and
Utilities.installPackageInDirectoryAsync, invoke the helper, and assert both are
called once, confirming the lock-acquisition and installation path is used.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@libraries/rush-lib/src/logic/test/InstallHelpers.test.ts`:
- Around line 129-250: Add a test in the ensureLocalPackageManagerAsync suite
covering an invalid or missing package-manager marker with no lock file. Do not
call writeInstalledPackageManagerAsync; mock LockFile.acquireAsync and
Utilities.installPackageInDirectoryAsync, invoke the helper, and assert both are
called once, confirming the lock-acquisition and installation path is used.

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📥 Commits

Reviewing files that changed from the base of the PR and between 8d872db and f5d1d4b.

📒 Files selected for processing (4)

• common/changes/@microsoft/rush/package-manager-install-lock_2026-06-23-13-27.json
• libraries/rush-lib/src/api/LastInstallFlag.ts
• libraries/rush-lib/src/logic/installManager/InstallHelpers.ts
• libraries/rush-lib/src/logic/test/InstallHelpers.test.ts