bug#36534: 25.2; mercurial vc-annotate sometimes fails when using the evolve mercurial extension

[Andrii Kolomoiets <andreyk.mad@gmail.com>]

Dmitry Gutov <dgutov@yandex.ru> writes:

> On 26.11.2020 13:56, Lars Ingebrigtsen wrote:
>> Valentin Gatien-Baron <valentin.gatienbaron@gmail.com> writes:
>> 
>>> Sometimes, vc-annotate in a file tracked by mercurial returns an
>>> error like this instead of a proper annotate buffer:
>> [...]
>> 
>>> Step 3 is probably an hg bug. However `hg parent` was deprecated in
>>> 2014, so people may be reluctant to change it. And it would be simpler
>>> for vc-hg-working-revision to call `hg log -r . -T {rev}` (vc-git does
>>> that, so I assume that it works in general on top of fixing the
>>> current issue). `.` means the current revision, see `hg help revset`.
>>>
>>> So something like this:
>>> (defun vc-hg-working-revision (file)
>>>    "Hg-specific version of `vc-working-revision'."
>>>    (ignore-errors
>>>      (with-output-to-string
>>>        (vc-hg-command standard-output 0 nil
>>>      "log" "-r" "." "--template" "{rev}"))))
>> (This bug report unfortunately got no response at the time.)
>> I'm pretty unfamiliar with Mercurial, but perhaps Dmitry has some
>> comments here (added to the Cc's).
>
> I have very little experience with Mercurial myself.
>
> Perhaps Daniel or Andrii can comment.

Valentin did a pretty good investigation here.

But proposed change make the `vc-hg-working-revision` function ignore
the FILE arg, so the result will differ.

1. mkdir working-revision
2. cd working-revision
3. hg init
4. echo a > a
5. hg commit -Am0
6. echo b > b
7. hg commit -Am1
8. hg parent --template {rev} a
   => 0
   This is the old behavior of the `vc-hg-working-revision`
9. hg log -r . --template {rev}
   => 1
   And this is the new one.

Not sure what it may leads to.  Indeed the `vc-git-working-revision`
function ignores FILE as well.