[PATCH v3] hg: allow usage of XDG_CONFIG_HOME and $HOME/.config/hg/hgrc

[Jun Wu]

Excerpts from David Demelier's message of 2017-02-08 17:41:50 +0100:
> # HG changeset patch
> # User David Demelier <demelier.david at gmail.com>
> # Date 1486485215 -3600
> #      Tue Feb 07 17:33:35 2017 +0100
> # Node ID 5ecf752f0a79482fe2cecfa73c5a733dab29fb88
> # Parent  1f51b4658f21bbb797e922d155c1046eddccf91d
> hg: allow usage of XDG_CONFIG_HOME and $HOME/.config/hg/hgrc
> 
> Modern applications must use the following paths to store configuration files:
> 
>   - $XDG_CONFIG_HOME/hg/hgrc
>   - $HOME/.config/hg/hgrc (if XDG_CONFIG_HOME is not set)
> 
> For convenience, these paths are now evaluated first and the old $HOME/.hgrc is
> used as a fallback.
> 
> See https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html 
> 
> diff -r 1f51b4658f21 -r 5ecf752f0a79 mercurial/help/config.txt
> --- a/mercurial/help/config.txt    Thu Feb 02 14:19:48 2017 +0100
> +++ b/mercurial/help/config.txt    Tue Feb 07 17:33:35 2017 +0100
> @@ -55,6 +55,8 @@
>    On Unix, the following files are consulted:
>  
>    - ``<repo>/.hg/hgrc`` (per-repository)
> +  - ``$XDG_CONFIG_HOME/hg/hgrc`` (per-user)
> +  - ``$HOME/.config/hg/hgrc`` (per-user)

This does not match the code logic. All files in the list should be loaded,
while the code only picks one of the three "per-user" files.

I think it's better to always include ~/.hgrc, even if $XDG_CONFIG_HOME
exists (also check the comment below). So the text here could be:

  - ${XDG_CONFIG_HOME:-$HOME/.config}/hg/hgrc
  - $HOME/.hgrc

>    - ``$HOME/.hgrc`` (per-user)
>    - ``<install-root>/etc/mercurial/hgrc`` (per-installation)
>    - ``<install-root>/etc/mercurial/hgrc.d/*.rc`` (per-installation)
> diff -r 1f51b4658f21 -r 5ecf752f0a79 mercurial/scmposix.py
> --- a/mercurial/scmposix.py    Thu Feb 02 14:19:48 2017 +0100
> +++ b/mercurial/scmposix.py    Tue Feb 07 17:33:35 2017 +0100
> @@ -40,8 +40,16 @@
>  def userrcpath():
>      if pycompat.sysplatform == 'plan9':
>          return [encoding.environ['home'] + '/lib/hgrc']
> +    elif pycompat.sysplatform == 'darwin':
> +        return [os.path.expanduser('~/.hgrc')]
>      else:
> -        return [os.path.expanduser('~/.hgrc')]
> +        home = encoding.environ.get('XDG_CONFIG_HOME',
> +            os.path.expanduser('~/.config'))

The XDG specification says:

  All paths set in these environment variables must be absolute. If an
  implementation encounters a relative path in any of these variables it
  should consider the path invalid and ignore it.

So it needs to be checked before use.

> +        path = os.path.join(home, 'hg/hgrc')
> +        if os.path.isfile(path):
> +            return [path]
> +        else:
> +            return [os.path.expanduser('~/.hgrc')]

This introduces a race condition:

  - hg: userrcpath() returns ~/.hgrc, but not $XDG_CONFIG_HOME/hg/hgrc
  - outside: somebody renames ~/.hgrc to $XDG_CONFIG_HOME/hg/hgrc
  - hg: user config file will be missed when actually reading the files

We can return both paths regardless of their existence, and avoid accessing
the filesystem in this function:

  confighome = encoding.environ.get('XDG_CONFIG_HOME')
  if not os.path.isabs(confighome):
      confighome = os.path.expanduser('~/.config')

  return [os.path.expanduser('~/.hgrc'),
          os.path.join(confighome, 'hg', 'hgrc')]

>  
>  def termsize(ui):
>      try:
> diff -r 1f51b4658f21 -r 5ecf752f0a79 tests/test-xdg.t
> --- /dev/null    Thu Jan 01 00:00:00 1970 +0000
> +++ b/tests/test-xdg.t    Tue Feb 07 17:33:35 2017 +0100
> @@ -0,0 +1,11 @@
> +#if no-windows no-osx
> +
> +  $ mkdir -p xdgconf/hg
> +  $ echo '[ui]' > xdgconf/hg/hgrc
> +  $ echo 'username = foobar' >> xdgconf/hg/hgrc
> +  $ XDG_CONFIG_HOME=xdgconf; export XDG_CONFIG_HOME
> +  $ unset HGRCPATH
> +  $ hg config ui.username
> +  foobar
> +
> +#endif