chore: ignore merge commits to target branch at tip of history

git-branch-linearity.sh

@@ -6,13 +6,26 @@ TARGET_BRANCH="${1:-main}"
 echo "Target branch: $TARGET_BRANCH"
 git fetch origin $TARGET_BRANCH 2> /dev/null
 
-out=$(git log origin/${TARGET_BRANCH}..HEAD --merges --oneline)
+
+# Detection of (PR) merge commits at tip of HEAD:
+target_sha=$(git rev-parse origin/${TARGET_BRANCH})
+# Get SHA of parent commit
+merge_target=$(git log --merges --oneline --parents --no-abbrev-commit HEAD^..HEAD | cut -d" " -f2)
+# If parent is the target branch, start from the commit before the merge commit
+if [ "$target_sha" = "$merge_target" ] ; then
+    tip="HEAD^"
+else
+    tip="HEAD"
+fi
+
+out=$(git log origin/${TARGET_BRANCH}..${tip} --merges --oneline)
 exit_status=$?
 if [ -n  "$out" ]
 then
     echo "Please rebase your branch" >&2
     echo "If your branch or its base branch is a release branch then ignore this error" >&2
-    echo "\nMerge commit(s):" >&2
+    echo >&2
+    echo "Merge commit(s):" >&2
     echo "$out" >&2
     # Disclaimer: current version of the check doesn't work well with release branches
     exit_status=1