[llvm] [Github] Set start rev to merge base in code format action (PR #75132)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-github-workflow

Author: Aiden Grossman (boomanaiden154)

<details>
<summary>Changes</summary>

This patch sets the start revision to the merge base so that the c++ formatting action won't produce any diffs related to changes in main but not in the PR branch. This also leaves a TODO to migrate over to the --diff_from_common_commit option in git-clang-format once LLVM v18 is released.

---
Full diff: https://github.com/llvm/llvm-project/pull/75132.diff


1 Files Affected:

- (modified) .github/workflows/pr-code-format.yml (+5-1) 


``````````diff
diff --git a/.github/workflows/pr-code-format.yml b/.github/workflows/pr-code-format.yml
index c27c282eb2a19a..5223089ee8a93d 100644
--- a/.github/workflows/pr-code-format.yml
+++ b/.github/workflows/pr-code-format.yml
@@ -67,10 +67,14 @@ jobs:
           START_REV: ${{ github.event.pull_request.base.sha }}
           END_REV: ${{ github.event.pull_request.head.sha }}
           CHANGED_FILES: ${{ steps.changed-files.outputs.all_changed_files }}
+        # TODO(boomanaiden154): Once clang v18 is released, we should be able
+        # to take advantage of the new --diff_from_common_commit option
+        # explicitly in code-format-helper.py and not have to diff starting at
+        # the merge base.
         run: |
           python ./code-format-tools/llvm/utils/git/code-format-helper.py \
             --token ${{ secrets.GITHUB_TOKEN }} \
             --issue-number $GITHUB_PR_NUMBER \
-            --start-rev $START_REV \
+            --start-rev $(git merge-base $START_REV $END_REV) \
             --end-rev $END_REV \
             --changed-files "$CHANGED_FILES"

``````````

</details>


https://github.com/llvm/llvm-project/pull/75132