dotnet/runtime · error · RuntimeError

Couldn't determine current git hash

Error message

Couldn't determine current git hash

What it means

Raised by determine_base_jit when 'git rev-parse HEAD' returns a nonzero exit code while running inside the runtime repo root (ChangeDir to runtime_repo_location). The current hash identifies the diff-side commit; without it, baseline computation cannot proceed. A nonzero code means git is unavailable, the directory is not a git repo, or the repo is in a broken state.

Solutions

  1. Confirm runtime_repo_location is a valid git clone: run 'git -C <runtime_repo_location> rev-parse HEAD' and ensure it succeeds.
  2. Ensure git is installed and on PATH in the execution environment.
  3. Clone the runtime repo via git rather than extracting a tarball so .git history exists.
  4. Pass --git_hash <sha> explicitly to skip the rev-parse step if you know the current commit.

Example fix

// before
command = ["git", "rev-parse", "HEAD"]
proc = subprocess.Popen(command, stdout=subprocess.PIPE)
stdout_git_rev_parse, _ = proc.communicate()
if proc.returncode != 0:
    raise RuntimeError("Couldn't determine current git hash")
// after (fix invocation)
git -C <runtime_repo_location> rev-parse HEAD   # must succeed
# Or pass the hash explicitly:
python superpmi.py asmdiff --git_hash <sha> ...
Defensive patterns

Strategy: validation

Validate before calling

import subprocess, shutil
def validate_git_head(repo_location):
    if shutil.which('git') is None:
        raise RuntimeError('git is not installed or not on PATH')
    proc = subprocess.run(['git', '-C', repo_location, 'rev-parse', 'HEAD'], capture_output=True)
    if proc.returncode != 0:
        raise RuntimeError(f"git rev-parse HEAD failed in {repo_location}: {proc.stderr.decode('utf-8','replace').strip()}")
    return proc.stdout.decode('utf-8').strip()

Prevention

When it happens

Trigger: subprocess.Popen(['git','rev-parse','HEAD']) runs and proc.returncode != 0, inside the runtime_repo_location. Happens when runtime_repo_location is not a git checkout, git is not installed/on PATH, the .git directory is missing/corrupt, or HEAD is unborn (empty repo after init with no commits).

Common situations: Downloading a source tarball instead of a git clone (no .git); running in a stripped container without git; pointing --runtime_repo_location at the wrong directory; a fresh repo with no commits.

Related errors

AI-assisted analysis of dotnet/runtime@60108ba66e (2026-08-10). Data as JSON: /api/errors/98769d8cd9289283. Report an issue: GitHub.

Appendix: source

Thrown at src/coreclr/scripts/superpmi.py:4868

    # We cache baseline jits under the following directory. Note that we can't create the full directory path
    # until we know the baseline JIT hash.
    default_basejit_root_dir = os.path.join(coreclr_args.spmi_location, "basejit")

    # Do all the remaining commands, including a number of 'git' commands including relative paths,
    # from the root of the runtime repo.

    with ChangeDir(coreclr_args.runtime_repo_location):
        if coreclr_args.git_hash is None:
            command = [ "git", "rev-parse", "HEAD" ]
            logging.debug("Invoking: %s", " ".join(command))
            proc = subprocess.Popen(command, stdout=subprocess.PIPE)
            stdout_git_rev_parse, _ = proc.communicate()
            return_code = proc.returncode
            if return_code == 0:
                current_hash = stdout_git_rev_parse.decode('utf-8').strip()
                logging.debug("Current hash: %s", current_hash)
            else:
                raise RuntimeError("Couldn't determine current git hash")
        else:
            current_hash = coreclr_args.git_hash

        if coreclr_args.base_git_hash is None:
            # We've got the current hash; figure out the baseline hash.
            # First find the newest hash for any branch matching */main.
            command = [ "git", "branch", "-r", "--sort=-committerdate", "-v", "--list", "*/main" ]
            logging.debug("Invoking: %s", " ".join(command))
            proc = subprocess.Popen(command, stdout=subprocess.PIPE)
            stdout_git_main_branch, _ = proc.communicate()
            return_code = proc.returncode
            if return_code != 0:
                raise RuntimeError("Couldn't determine newest 'main' git hash")

            main_hash = stdout_git_main_branch.decode('utf-8').strip().split()[1]

            # Get the merge-base between the newest main and our current rev
            command = [ "git", "merge-base", current_hash, main_hash ]

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