[PATCH stable] pycompat: fix crash when default locale is unknown

[Yuya Nishihara]

On Wed, 24 Jun 2020 04:25:57 +0200, Manuel Jacob wrote:
> # HG changeset patch
> # User Manuel Jacob <me at manueljacob.de>
> # Date 1592965534 -7200
> #      Wed Jun 24 04:25:34 2020 +0200
> # Branch stable
> # Node ID 5d2b9295f7607e6f1bc6004af2948f95c83ec4ee
> # Parent  3d41172f2ac9ae7b644f3e5f239c28e895f1c4fa
> # EXP-Topic locale
> pycompat: fix crash when default locale is unknown
> 
> Instead, fall back to the filesystem encoding if the default locale is unknown.
> 
> diff --git a/mercurial/pycompat.py b/mercurial/pycompat.py
> --- a/mercurial/pycompat.py
> +++ b/mercurial/pycompat.py
> @@ -178,9 +178,16 @@
>          if os.name == r'nt':
>              sysargv = [a.encode("mbcs", "ignore") for a in sys.argv]
>          else:
> +
> +            def getdefaultlocale_if_known():
> +                try:
> +                    return locale.getdefaultlocale()
> +                except ValueError:
> +                    return None, None
> +
>              encoding = (
>                  locale.getlocale()[1]
> -                or locale.getdefaultlocale()[1]
> +                or getdefaultlocale_if_known()[1]

Seems fine, but it might be more correct to remove getdefaultlocale() at all.

The comment mentions mbstowcs(), which is a locale-dependent function.
If setlocale(LC_CTYPE, '') wouldn't be called yet, I think mbstowcs()
would behave as if the locale were C. So locale.getlocale(LC_CTYPE) should
return the encoding which mbstowcs() would see.