Working directory may be corrupted when process dies while .git/config.lock exists and checkout will always fail

[thomasjahoda]

If the process dies while updating the local Git config file, the working directory for the current runner may be corrupted (.git/config.lock keeps existing) and actions/checkout@v4 will always fail.

We had the following error while running a GitHub action in a Docker container:

Run actions/checkout@v4
[...]
Setting up auth
  [...]
  Error: error: could not lock config file .git/config: File exists

How to reproduce

Create the lockfile in the action-runner working directory: touch .git/config.lock to simulate the corrupted state when the process dies during checkout.
Start some workflow running "actions/checkout@v4".

Expected behavior

actions/checkout@v4 detects the corrupted state and removes the whole repository.

Actual behavior

Error.

Workaround

Manually clean the working directory of the action-runner.