hgext/hooklib/reject_new_heads.py

streamclone: avoid some obscure error in a corner case

I don't really know how, but I ran into this error:

    $ hg clone --stream ssh://user@dummy/empty-repo local-empty-repo
    streaming all changes
    abort: unable to apply stream clone: unsupported format:
    [255]

I think you need an empty list of requirements for this to happen,
which is weird, but an obscure error like this is not exactly helpful
either. Since this is the result of an encoding bug anyway, just fix
it.

Differential Revision: https://phab.mercurial-scm.org/D12402

# Copyright 2020 Joerg Sonnenberger <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

"""reject_new_heads is a hook to check that branches touched by new changesets
have at most one open head. It can be used to enforce policies for
merge-before-push or rebase-before-push. It does not handle pre-existing
hydras.

Usage:
  [hooks]
  pretxnclose.reject_new_heads = \
    python:hgext.hooklib.reject_new_heads.hook
"""

from __future__ import absolute_import

from mercurial.i18n import _
from mercurial import (
    error,
    pycompat,
)


def hook(ui, repo, hooktype, node=None, **kwargs):
    if hooktype != b"pretxnclose":
        raise error.Abort(
            _(b'Unsupported hook type %r') % pycompat.bytestr(hooktype)
        )
    ctx = repo.unfiltered()[node]
    branches = set()
    for rev in repo.changelog.revs(start=ctx.rev()):
        rev = repo[rev]
        branches.add(rev.branch())
    for branch in branches:
        if len(repo.revs("head() and not closed() and branch(%s)", branch)) > 1:
            raise error.Abort(
                _(b'Changes on branch %r resulted in multiple heads')
                % pycompat.bytestr(branch)
            )