hgext/hooklib/enforce_draft_commits.py

wireprototypes: make `baseprotocolhandler` methods abstract

The documentation says it's an abstract base class, so let's enforce it.  The
`typing.Protocol` class is already an ABC, but it only prevents instantiation if
there are abstract attrs that are missing.  For example, from `hg debugshell`:

    >>> from mercurial import wireprototypes
    >>> x = wireprototypes.baseprotocolhandler()
    Traceback (most recent call last):
      File "<console>", line 1, in <module>
    TypeError: Can't instantiate abstract class baseprotocolhandler with abstract method name
    >>> class fake(wireprototypes.baseprotocolhandler):
    ...     pass
    ...
    >>> x = fake()
    Traceback (most recent call last):
      File "<console>", line 1, in <module>
    TypeError: Can't instantiate abstract class fake with abstract method name

That's great, but it doesn't protect against calling non-abstract methods at
runtime, rather it depends on the protocol type hint being added to method
signatures or class attrs, and then running a type checker to notice when an
instance is assigned that doesn't conform to the protocol.  We don't widely use
type hints yet, and do have a lot of class hierarchy in the repository area,
which could lead to surprises like this:

    >>> class fake(wireprototypes.baseprotocolhandler):
    ...     @property
    ...     def name(self) -> bytes:
    ...         return b'name'
    ...
    >>> z = fake()
    >>> z.client()
    >>> print(z.client())
    None

Oops.  That was supposed to return `bytes`.  So not only is a bad/unexpected
value returned, but it's one that violates the type hints (since the base
client() method will be annotated to return bytes).  With this change, we get:

    >>> from mercurial import wireprototypes
    >>> class fake(wireprototypes.baseprotocolhandler):
    ...     @property
    ...     def name(self) -> bytes:
    ...         return b'name'
    ...
    >>> x = fake()
    Traceback (most recent call last):
      File "<console>", line 1, in <module>
    TypeError: Can't instantiate abstract class fake with abstract methods
        addcapabilities, checkperm, client, getargs, getpayload, getprotocaps, mayberedirectstdio

So this looks like a reasonable safety harness to me, and lets us catch problems
by running the standard tests while the type hints are being added, and pytype
is improved.  We should probably do this for all Protocol class methods that
don't supply a method implementation.

# 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.

"""enforce_draft_commits us a hook to ensure that all new changesets are
in the draft phase. This allows enforcing policies for work-in-progress
changes in overlay repositories, i.e. a shared hidden repositories with
different views for work-in-progress code and public history.

Usage:
  [hooks]
  pretxnclose-phase.enforce_draft_commits = \
    python:hgext.hooklib.enforce_draft_commits.hook
"""

from __future__ import annotations

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


def hook(ui, repo, hooktype, node=None, **kwargs):
    if hooktype != b"pretxnclose-phase":
        raise error.Abort(
            _(b'Unsupported hook type %r') % pycompat.bytestr(hooktype)
        )
    ctx = repo.unfiltered()[node]
    if kwargs['oldphase']:
        raise error.Abort(
            _(b'Phase change from %r to %r for %s rejected')
            % (
                pycompat.bytestr(kwargs['oldphase']),
                pycompat.bytestr(kwargs['phase']),
                ctx,
            )
        )
    elif kwargs['phase'] != b'draft':
        raise error.Abort(
            _(b'New changeset %s in phase %r rejected')
            % (ctx, pycompat.bytestr(kwargs['phase']))
        )