Add ability to show which projects would hit cache

[rlmestre]

• I'd be willing to implement this feature (contributing guide)

Description

When using nx run-many or similar commands, there's no way to predetermine which runs would be retrieved from the cache and which ones wouldn't without running them.

Motivation

Similar to why nx show projects --affected (previously nx print-affected --select=projects) exists: knowing which outputs need recomputation in advance may be useful for control flow or other reasons.

I've thought about this to avoid stalling git hooks for reasons that aren't git-related. We have a pre-push hook that checks if linting passes for affected projects. When many projects need recomputation it takes a while which, even though engineers are aware of why it does, it's not ideal.

Checking if the targets are in the cache would let us short-circuit the process. We can have the git hook only check if all runs are in the cache and otherwise fail so the developer runs the process separately and have the cache rebuilt.

Suggested Implementation

A flag for nx show similar to -affected would probably be ideal:
nx show projects --cached --target=test

Alternate Implementations

None

Related

#6681 (closed as stale)

[mayteio]

+1 on this. I'd love to skip some code-generation tasks in CI if I know ahead of time that all tasks will hit the cache.

[LuminusDev]

+1

[FrozenPandaz]

The reality is that there is no way to predetermine this. Nx waits until the last minute, right before running the task, to determine if it can reuse the cache. This is tasks can depend on the outputs of other tasks which would be run before it. So without running tasks, we don't know for certain if something is able to pull from cache.