SDK cache hit can restore an incompatible older layout and still download Flutter

[dtussupbayev]

Hi. I ran into this while moving a workflow from the temporary .fvmrc support commit to v2.

Setup:

- uses: subosito/flutter-action@v2
  with:
    flutter-version-file: .fvmrc
    cache: true

.fvmrc:

{
  "flutter": "3.35.6"
}

v2 currently resolves to 1a449444c387b1966244ae4d4f8c696479add0b2 / v2.23.0 for me.

What I saw:

• Cache Flutter reported a hit for the default SDK key, like flutter-linux-stable-3.35.6-x64-....
• Right after restoring that cache, the setup step still downloaded the Flutter archive again (100 1372M).
• So the step paid both costs: restoring the SDK cache and downloading/extracting the SDK again.

The relevant log shape was:

Cache hit for: flutter-linux-stable-3.35.6-x64-...
Cache restored successfully
...
$GITHUB_ACTION_PATH/setup.sh ...
100 1372M  100 1372M ...

I checked the action code and I think this is caused by the SDK layout change in the cache path:

• the temporary commit 6622f58c checks/uses CACHE_PATH/bin/flutter
• current v2 checks/uses CACHE_PATH/flutter/bin/flutter

The default SDK cache key did not change, so v2 can restore a cache that was created by the older layout. Since that is a primary-key cache hit, actions/cache will not replace it with the new layout at the end of the job.

I verified this by changing only the SDK cache key prefix in our workflow. First run was a cold miss and saved a new cache. The rerun restored the new cache and did not download the Flutter archive again.

Rough timings from the same workflow:

old temporary commit, SDK cache hit:   Set up Flutter ~26s
v2, default key, old cache restored:   Set up Flutter ~1m33s
v2, fresh SDK cache key, rerun hit:    Set up Flutter ~32s

Would it make sense to bump/version the default SDK cache key after the layout change, or handle the old layout as a fallback before downloading the SDK again?

[kuhnroyal]

This is not caused by v2 in general, it is caused by my recent change in #379 - clear the caches and you will be fine for future runs.

[dtussupbayev]

Confirmed on our side after clearing the repository Actions caches. The next run created a fresh flutter-linux-stable-3.35.6-x64-... SDK cache, and the rerun restored that cache without downloading the Flutter archive again.

So this was indeed a stale cache created before #379. Closing this. Thanks for the quick clarification.