How to use the ghstack.git.GitCommitHash function in ghstack

if not rewriting and not should_unlink:
            # Advance HEAD without reconstructing commit
            head = commit_id
            continue

        rewriting = True
        commit_msg = s.commit_msg()
        logging.debug("-- commit_msg:\n{}".format(textwrap.indent(commit_msg, '   ')))
        if should_unlink:
            commit_msg = RE_GHSTACK_SOURCE_ID.sub(
                '',
                ghstack.diff.RE_PULL_REQUEST_RESOLVED_W_SP.sub('', commit_msg)
            )
            logging.debug("-- edited commit_msg:\n{}".format(
                textwrap.indent(commit_msg, '   ')))
        head = GitCommitHash(sh.git(
            "commit-tree",
            s.tree(),
            "-p", head,
            input=commit_msg))

    sh.git('reset', '--soft', head)

    logging.info("""
Diffs successfully unlinked!

To undo this operation, run:

    git reset --soft {}
""".format(s.commit_id()))

    return head

# If commits is empty, we unlink the entire stack
    #
    # For now, we only process commits on our current
    # stack, because we have no way of knowing how to
    # "restack" for other commits.

    if sh is None:
        # Use CWD
        sh = ghstack.shell.Shell()

    # Parse the commits
    parsed_commits: Optional[Set[GitCommitHash]] = None
    if commits:
        parsed_commits = set()
        for c in commits:
            parsed_commits.add(GitCommitHash(sh.git("rev-parse", c)))

    base = GitCommitHash(sh.git("merge-base", "origin/master", "HEAD"))

    # compute the stack of commits in chronological order (does not
    # include base)
    stack = ghstack.git.split_header(
        sh.git("rev-list", "--reverse", "--header", "^" + base, "HEAD"))

    # sanity check the parsed_commits
    if parsed_commits is not None:
        stack_commits = set()
        for s in stack:
            stack_commits.add(s.commit_id())
        invalid_commits = parsed_commits - stack_commits
        if invalid_commits:
            raise RuntimeError(

# For now, we only process commits on our current
    # stack, because we have no way of knowing how to
    # "restack" for other commits.

    if sh is None:
        # Use CWD
        sh = ghstack.shell.Shell()

    # Parse the commits
    parsed_commits: Optional[Set[GitCommitHash]] = None
    if commits:
        parsed_commits = set()
        for c in commits:
            parsed_commits.add(GitCommitHash(sh.git("rev-parse", c)))

    base = GitCommitHash(sh.git("merge-base", "origin/master", "HEAD"))

    # compute the stack of commits in chronological order (does not
    # include base)
    stack = ghstack.git.split_header(
        sh.git("rev-list", "--reverse", "--header", "^" + base, "HEAD"))

    # sanity check the parsed_commits
    if parsed_commits is not None:
        stack_commits = set()
        for s in stack:
            stack_commits.add(s.commit_id())
        invalid_commits = parsed_commits - stack_commits
        if invalid_commits:
            raise RuntimeError(
                "unlink can only process commits which are on the "
                "current stack; these commits are not:\n{}"

def main(commits: Optional[List[str]] = None,
         sh: Optional[ghstack.shell.Shell] = None) -> GitCommitHash:
    # If commits is empty, we unlink the entire stack
    #
    # For now, we only process commits on our current
    # stack, because we have no way of knowing how to
    # "restack" for other commits.

    if sh is None:
        # Use CWD
        sh = ghstack.shell.Shell()

    # Parse the commits
    parsed_commits: Optional[Set[GitCommitHash]] = None
    if commits:
        parsed_commits = set()
        for c in commits:
            parsed_commits.add(GitCommitHash(sh.git("rev-parse", c)))

    base = GitCommitHash(sh.git("merge-base", "origin/master", "HEAD"))

    # compute the stack of commits in chronological order (does not
    # include base)
    stack = ghstack.git.split_header(
        sh.git("rev-list", "--reverse", "--header", "^" + base, "HEAD"))

    # sanity check the parsed_commits
    if parsed_commits is not None:
        stack_commits = set()
        for s in stack: