Make global transforms cache versioned

[lptr]

Currently the output of global artifact transforms are stored under $GRADLE_HOME/caches/transforms-2 which is a cross-version cache location. However, the locations of the individual workspaces are bound to the Gradle version executing the related transforms. Thus there is no chance of different versions reusing content from this cache directory.

To complicate matters more, the state of the workspaces is tracked via the global version-bound executionHistory.

Therefore the cache should actually be a non-cross-version cache, and be moved under $GRADLE_HOME/$GRADLE_VERSION/caches/transforms (or similar).

One downside of doing this is that after upgrading to a new version of Gradle the old caches won't be cleaned up anymore, which could end up wasting disk space. This is not a special case for the transforms cache, but it's a potentially large cache where the effect is perhaps more visible. We should handle this problem separately though.

---

cc: @gradle/build-cache

[wolfs]

I think we already clean up version specific caches of older Gradle versions when the older version hasn't been used for a certain amount of time.

[lptr]

As discussed with @wolfs we should probably also migrate to a different layout. Right now we have the following layout:

- $GRADLE_HOME/caches/transforms-2/
  - files-2.1/
    - <HASH>/  <---- output directory for the transform
    - <HASH>.bin <-- result file for the transform

We could move to this:

- $GRADLE_HOME/$GRADLE_VERSION/caches/transforms/
  - <HASH>  <-------- workspace root
    - output/  <----- output directory for the transform
    - results.bin <-- result file for the transform

There is no real need for the files-2.1 directory, so let's do away with that. OTOH, it would be nicer to have a single root/entity for every workspace. It just makes more sense to me for one, and if we want to make the cache atomic (so a failed execution won't be able to corrupt it), we need a single root anyway.

[lptr]

I've added a generic workspace allocator in this (currently draft) PR that we can eventually migrate to: #12072

[stale]

This issue has been automatically marked as stale because it has not had recent activity. Given the limited bandwidth of the team, it will be automatically closed if no further activity occurs. If you're interested in how we try to keep the backlog in a healthy state, please read our blog post on how we refine our backlog. If you feel this is something you could contribute, please have a look at our Contributor Guide. Thank you for your contribution.

[lptr]

We should do this.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. Given the limited bandwidth of the team, it will be automatically closed if no further activity occurs. If you're interested in how we try to keep the backlog in a healthy state, please read our blog post on how we refine our backlog. If you feel this is something you could contribute, please have a look at our Contributor Guide. Thank you for your contribution.