Add merge conflict github PR check

[mbykhovtsev-ms]

Merge Checklist

All boxes should be checked before merging the PR (just tick any boxes which don't apply to this PR)

• [x] The toolchain has been rebuilt successfully (or no changes were made to it)
• [x] The toolchain/worker package manifests are up-to-date
• [x] Any updated packages successfully build (or no packages were changed)
• [x] Packages depending on static components modified in this PR (Golang, *-static subpackages, etc.) have had their Release tag incremented.
• [x] Package tests (%check section) have been verified with RUN_CHECK=y for existing SPEC files, or added to new SPEC files
• [x] All package sources are available
• [x] cgmanifest files are up-to-date and sorted (./cgmanifest.json, ./toolkit/scripts/toolchain/cgmanifest.json, .github/workflows/cgmanifest.json)
• [x] LICENSE-MAP files are up-to-date (./LICENSES-AND-NOTICES/SPECS/data/licenses.json, ./LICENSES-AND-NOTICES/SPECS/LICENSES-MAP.md, ./LICENSES-AND-NOTICES/SPECS/LICENSE-EXCEPTIONS.PHOTON)
• [x] All source files have up-to-date hashes in the *.signatures.json files
• [x] sudo make go-tidy-all and sudo make go-test-coverage pass
• [x] Documentation has been updated to match any changes to the build system
• [x] Ready to merge

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Summary

Added merge conflict PR check to catch case of cherry-pick tools committing merge conflicts to fix bug https://microsoft.visualstudio.com/OS/_workitems/edit/53883399

Change Log

• Added merge conflict PR check to catch case of cherry-pick tools committing merge conflicts

Does this affect the toolchain?

NO

Example of simulated committed merge conflict https://github.com/microsoft/azurelinux/actions/runs/11584391919/job/32251428087

[reubeno]

Naive question: have we explored the native facilities that GitHub provides to ensure that changes aren't in conflict / that the PR branch is up to date with incoming changes in the target branch? Or is there some use case that you're targeting that's not covered by those?

[mbykhovtsev-ms]

Naive question: have we explored the native facilities that GitHub provides to ensure that changes aren't in conflict / that the PR branch is up to date with incoming changes in the target branch? Or is there some use case that you're targeting that's not covered by those?

Yeah, I am targeting in particular edge case of the fast track cherry-pick tool we have, it is the one that would commit merge conflicts and create PRs with them. A different approach might be to make that tool not create PRs and push merge conflicts in the first place, but then it would block the cherry-pick process via tool when any merge conflicts are present that needs to be resolved and will require it be done manually. I believe such edge case is not entirely rare A PR check was a suggestion in this bug by Henry https://microsoft.visualstudio.com/OS/_workitems/edit/53883399.

What other native facilities that Github provides do you suggest?

[reubeno]

Ah, I didn't realize this was primarily for cherry picks; thanks for the explanation. With that context, I'd agree it's a good idea to prevent unresolved (but already merged) conflicts from getting checked in (i.e., what you're doing here). I also think it's a good idea to pursue how to improve the cherry-picking process to avoid them getting committed in the first place, but agree that's more complicated and separable.