Can I prevent cache generation and saving if it matches the restore key?

[hkusu]

Cache is generated even when the restore key is applied.

There is a cache capacity limit (10G), so in that case I don't want to generate a cache, but is there any way?

It would also be nice to have a feature like read-only that doesn't generate cache even if it doesn't match the restore key.

[henrygab]

Yes, please!!!

Here's an actual use case:

1. scheduled job runs actions/cache with a fixed, never-to-be-used key, and with restore-keys listing only the common prefix (e.g., force miss + use of restore key to get latest version)
2. workflow runs install / update / upgrade items
3. workflow generate a new hash, based on the new files
4. if new hash matches hard-coded expected hash:
   workflow exits successfully (but without creating a new cache!!!)
5. workflow runs actions/cache a second time, now using using the prefix + new hash ... with the expectation that this would create the cache using the prefix + new hash
6. workflow opens an issue (later: maybe a full PR) in the repository, indicating the new hash that needs to be used in the affected workflow(s)

Basically, there is a need to disable automatic cache creation. Put another way, there needs to be an option to run the action in a "read-only" mode, where all it does is attempt to restore a cache, if a match can be found.

Without this ability to prevent cache generation, the cache system breaks for many uses.