[build-tools] Cache Gradle file access time journal with the build cache

[sjchmiela]

Why

It seems the cache is not getting pruned properly. It looks like Gradle uses journal to keep track of accessed files. Since we're not caching it alongside build cache, Gradle defaults all files to "they have been used now".

How

When caching Gradle build cache, cache journal too.

Test Plan

Verified locally.

[codecov]

Codecov Report

❌ Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.64%. Comparing base (6cbddf5) to head (1fe1698).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
.../build-tools/src/steps/functions/saveBuildCache.ts	0.00%	2 Missing ⚠️
...ild-tools/src/steps/functions/restoreBuildCache.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4221      +/-   ##
==========================================
+ Coverage   63.53%   63.64%   +0.11%     
==========================================
  Files        1028     1028              
  Lines       47033    47059      +26     
  Branches     9884     9891       +7     
==========================================
+ Hits        29879    29944      +65     
+ Misses      17053    17014      -39     
  Partials      101      101              

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[Copilot]

Pull request overview

Updates the build-cache save/restore workflow in @expo/build-tools so cache archives preserve per-file mtimes across the copy-to-temp + tar round trip, which is required for Gradle’s mtime-based cache pruning (LRU-style cleanup) to keep working.

Changes:

• Preserve file atime/mtime when copying cache entries into the temporary staging directory prior to creating the tarball.
• Add a Jest test that validates mtimes survive the compress + decompress round trip.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
packages/build-tools/src/steps/functions/saveCache.ts	Preserves timestamps on copied cache files before archiving so Gradle cleanup logic can rely on mtimes.
packages/build-tools/src/steps/functions/tests/saveRestoreCache.test.ts	Adds a regression test asserting that mtimes survive cache compress/decompress.

Suppressed comments (2)

packages/build-tools/src/steps/functions/tests/saveRestoreCache.test.ts:35

• Same as above: cache-restore is a fixed path under os.tmpdir(), which can collide across test runs. Use mkdtemp for a unique directory (and avoid the separate mkdir).

    const restoreDir = path.join(os.tmpdir(), 'cache-restore');
    await fs.promises.mkdir(restoreDir, { recursive: true });

packages/build-tools/src/steps/functions/tests/saveRestoreCache.test.ts:45

• The test currently leaves behind temp directories and the generated archive on success, which can accumulate in CI/dev machines. Consider removing them at the end of the test (or via a finally/afterEach).

    const restoredStat = await fs.promises.stat(path.join(restoreDir, 'entry.txt'));
    expect(Math.floor(restoredStat.mtimeMs / 1000)).toBe(Math.floor(mtime.getTime() / 1000));
  });

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

Suppressed comments (2)

packages/build-tools/src/steps/functions/tests/saveRestoreCache.test.ts:50

• The test leaves temporary directories and the generated tar archive on disk. Cleaning them up avoids leaking /tmp contents and keeps repeated runs stable.

      await fs.promises.readFile(
        path.join(restoreDir, 'journal-1', 'file-access.properties'),
        'utf8'
      )
    ).toBe('inception=1');
  });

packages/build-tools/src/steps/functions/tests/saveRestoreCache.test.ts:39

• This test uses fixed paths under os.tmpdir() (e.g. /tmp/gradle-caches), which can collide across parallel test runs and can also pick up leftover files from earlier runs. Use fs.promises.mkdtemp to create unique per-test directories and avoid flakiness.

This issue also appears on line 45 of the same file.

    const cachesDir = path.join(os.tmpdir(), 'gradle-caches');
    const buildCacheDir = path.join(cachesDir, 'build-cache-1');
    const journalDir = path.join(cachesDir, 'journal-1');
    await fs.promises.mkdir(buildCacheDir, { recursive: true });
    await fs.promises.mkdir(journalDir, { recursive: true });

[github-actions]

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