Remove path limitation and adjust skip-actions logic in clang-tidy job

[kevingranade]

Summary

None

Purpose of change

Tried making the "clang-tidy (src)" job mandatory (again), was reminded that if the job never runs the system counts that as a failure or at least a not-pass.
While looking at docs for skip-duplicate-actions I found that required matrix jobs require special handling https://github.com/marketplace/actions/skip-duplicate-actions#how-to-use-skip-check-with-required-matrix-jobs

Describe the solution

Don't use GHA path-based optional triggering for the job, it has to run on every PR now.
Adjust skip-duplicate-actions logic to skip just the (expensive) clang-tidy step instead of the whole job, this allows the matrix job to run but be marked as a success despite being skipped.

Describe alternatives you've considered

Do we really need clang-tidy to be mandatory? Yes we do, it breaking all the time is a pain.

Testing

This just makes things more permissive, so the failure mode is if we have types of changes that erroneously trigger a full clang-tidy check somehow.

Additional context

In-flight non-cpp changes will need to be rebased to pick this up before we mark the clang-tidy job as required again, otherwise their lack of a required check will block merging.
I'm not in a HUUUGE hurry to do so, so we can take our time a bit, but we will definitely need to do some amount of rebasing.

[akrieger]

Eventually we should also make it so it doesn't build clang-tidy even on cpp changes if none of the cpp changes are relevant, to save another few minutes.

[kevingranade]

Oh is that minutes? I can patch that in then, I just didn't want to clutter the hell out of the job def.

[akrieger]

clang-tidy step starts at 16:40:06 https://github.com/CleverRaven/Cataclysm-DDA/actions/runs/12164255058/job/33925480223#step:9:1
building depfiles starts at 16:42:46, 2m40s potential savings. https://github.com/CleverRaven/Cataclysm-DDA/actions/runs/12164255058/job/33925480223#step:9:272

[akrieger]

Sorry I meant when we actually invoke clang-tidy.sh, we spend 2:30s building cata clang tidy plugins and running their tests, only to possibly just skip running tidy because eg. only third party sources or json were touched. The steps you just skipped are only some seconds.

[kevingranade]

Oh I misread you, yea it looks like we can move to https://github.com/marketplace/actions/skip-duplicate-actions#changed_files for skipping based on analyzing the paths that actually changed, and I think that should happen later.

I made a productive change based on the misreading though, I updated it to skip the clang-tidy build step and a step that will probably fail if the build step is skipped if there are no cpp files changed since you pointed out it's not super cheap.

[kevingranade]

Double misread you :)
Yea we can also do some surgery on the script to try and exit earlier without wasted effort, we can probably build the include files and analyze the changes before building clang-tidy itself.