fatal: origin/main...HEAD: no merge baseThis Git error appears when the workflow tries to compute the merge base between the branch under test (HEAD) and the requested base ref (for example origin/main), but the local checkout does not contain a common ancestor commit. In GitHub Actions this typically happens when both refs are fetched with a very shallow history (for example --depth=1), so the shared merge base commit is not available locally.
To resolve it:
- Fetch the base ref with a larger depth or unshallow the repository (e.g. git fetch origin "$BASE_REF" --deepen=50 or git fetch --unshallow) before running commands that need a merge base.
- Ensure BASE_REF points to the correct upstream branch and that your feature branch is descended from it.
Increasing the fetch depth restores the missing ancestor commit so git merge-base origin/main HEAD can succeed.
