use correct commits for diff

Author: microdev1

.github/workflows/build.yml

@@ -67,11 +67,9 @@ jobs:
       run: echo "HEAD_SHA=${{ github.event.pull_request.head.sha }}" >> $GITHUB_ENV
     - name: Set base sha (pull)
       if: github.event_name == 'pull_request'
-      run: |
-        git fetch --no-tags --no-recurse-submodules --depth=$((DEPTH + 1)) origin $HEAD_SHA
-        echo "BASE_SHA=$(git rev-list $HEAD_SHA --skip=$DEPTH --max-count=1)" >> $GITHUB_ENV
+      run: git cat-file -e $SHA && echo "BASE_SHA=$SHA" >> $GITHUB_ENV || true
       env:
-        DEPTH: ${{ steps.get-last-commit-with-checks.outputs.commit_depth || github.event.pull_request.commits }}
+        SHA: ${{ steps.get-last-commit-with-checks.outputs.commit_sha || github.event.pull_request.base.sha }}
     - name: Set head sha (push)
       if: github.event_name == 'push'
       run: echo "HEAD_SHA=${{ github.event.after }}" >> $GITHUB_ENV

tools/ci_set_matrix.py

@@ -89,7 +89,7 @@ def git_diff(pattern: str):
     print("Using files list by computing diff")
     changed_files = git_diff("$BASE_SHA...$HEAD_SHA")
     if os.environ.get("GITHUB_EVENT_NAME") == "pull_request":
-        changed_files.intersection_update(git_diff("$HEAD_SHA~...$HEAD_SHA"))
+        changed_files.intersection_update(git_diff("$GITHUB_SHA~...$GITHUB_SHA"))
 else:
     print("Using files list in CHANGED_FILES")
     changed_files = set(json.loads(os.environ.get("CHANGED_FILES") or "[]"))