bug#62663: 28.2; vc-hg-state returns incorrect results on directories in some repos

bug#62663: 28.2; vc-hg-state returns incorrect results on directories in some repos

[Spencer Baugh]

The problem is with vc-hg-state-fast, which parses Mercurial data
structures instead of shelling out to hg.  This is a great idea but our
parsing seems to be wrong right now in some way.

1. Create a new hg repo with:

hg init
  --config format.use_share_safe=false
  --config format.use-persistent-nodemap=false
  --config format.sparse-revlog=false
  --config format.revlog-compression=zlib

(This is disabling some recent hg features which make vc-hg-state use
the slow path.  You can verify that vc-hg-state-fast is going to run by
checking that .hg/requirements is a subset of
vc-hg-supported-requirements)

2. touch foo && hg add foo && hg commit -m.
3. (vc-hg-state-slow ".")
Returns 'up-to-date which is correct (because it shells out to hg)
4. (vc-hg-state ".")
Returns 'unregistered which is wrong

To a user, this manifests as various hg commands failing with errors,
often something like
"vc-find-backend-function: Cannot open load file: No such file or directory, vc-nil"

This also happens on Emacs 29.

(Note that this is independent of my other bug about lack of support for
certain repo requirements.  That bug is about expanding vc-hg-state-fast
support to new repos; this bug is showing that the already existing
support is buggy!)


In GNU Emacs 28.2 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version 1.15.12, Xaw scroll bars)
 of 2023-02-09 built on igm-qws-u12685a
Repository revision: 739b5d0e52d83ec567bd61a5a49ac0e93e0eb469
Repository branch: HEAD
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: CentOS Linux 7 (Core)

Configured using:
 'configure --with-x-toolkit=lucid --without-gpm --without-gconf
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 --with-cairo --with-rsvg
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bug#62663: 28.2; vc-hg-state returns incorrect results on directories in some repos

[Dmitry Gutov]

Hi! Thanks for the report.

On 04/04/2023 17:05, Spencer Baugh wrote:
> The problem is with vc-hg-state-fast, which parses Mercurial data
> structures instead of shelling out to hg.  This is a great idea but our
> parsing seems to be wrong right now in some way.
> 
> 1. Create a new hg repo with:
> 
> hg init
>    --config format.use_share_safe=false
>    --config format.use-persistent-nodemap=false
>    --config format.sparse-revlog=false
>    --config format.revlog-compression=zlib
> 
> (This is disabling some recent hg features which make vc-hg-state use
> the slow path.  You can verify that vc-hg-state-fast is going to run by
> checking that .hg/requirements is a subset of
> vc-hg-supported-requirements)
> 
> 2. touch foo && hg add foo && hg commit -m.
> 3. (vc-hg-state-slow ".")
> Returns 'up-to-date which is correct (because it shells out to hg)
> 4. (vc-hg-state ".")
> Returns 'unregistered which is wrong
> 
> To a user, this manifests as various hg commands failing with errors,
> often something like
> "vc-find-backend-function: Cannot open load file: No such file or directory, vc-nil"
> 
> This also happens on Emacs 29.
> 
> (Note that this is independent of my other bug about lack of support for
> certain repo requirements.  That bug is about expanding vc-hg-state-fast
> support to new repos; this bug is showing that the already existing
> support is buggy!)

Patches are welcome, of course.

I'm going to Cc the original author of that code, but that's just for 
courtesy.