Bug#1051373: libglib2.0-0: 2.77.3-1 breaks Midnight Commander extension file

[Simon McVittie]

Control: tags -1 + upstream
Control: clone -1 -2 -3
Control: reassign -2 mc 3:4.8.29-2
Control: retitle -2 mc: Regex key in mc.ext.ini expects GLib to use non-standard Desktop Entry parsing
Control: reassign -3 notmuch
Control: retitle -3 notmuch: expects GLib to use non-standard Desktop Entry parsing
Control: tags -1 + fixed-upstream pending

On Wed, 06 Sep 2023 at 22:49:52 +0000, Michael Gold wrote:
> 
> After upgrading libglib2.0-0 from 2.77.2-1 to 2.77.3-1, I'm no longer
> able to open files by selecting them in Midnight Commander and pressing
> Enter.  A change in the behaviour of g_key_file_get_string() appears to
> be the cause.  For example, one section of the mc.ext.ini file contains:
> 	[pdf]
> 	Regex=\.(pdf|PDF|ps|djvu)$
> 	Open=pdf %f &

If whatever program is loading this file (presumably mc) is parsing
Regex as if it was the 'string' or 'localestring' type from the Desktop
Entry Specification[1], then this is not syntactically valid Desktop
Entry syntax: in a 'string' or 'localestring', backslashes that are not
part of one of the known escapes \s, \n, \t, \r or \\ must be doubled.
GLib's g_key_file_get_string() is designed to load a 'string' or
'localestring' from a .desktop file, or a file in a compatible format.

[1] https://specifications.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html#value-types

Or, if mc wants to get everything after the "=" (and do its own
unescaping, if any), then it should call g_key_file_get_value(), which
does not process those backslash escapes, instead of
g_key_file_get_string(); or it could use a different .ini-style parser
if that's what is preferred. I'm told this is being discussed upstream,
but I don't have a specific bug reference for that.

notmuch is apparently also affected by this and needs to make a similar
choice: https://gitlab.gnome.org/GNOME/glib/-/issues/3094#note_1839232

GLib 2.77.3 made the error behaviour of g_key_file_get_string()
more conventional, triggering this regression. GLib 2.78.0 reverts
that change (see https://gitlab.gnome.org/GNOME/glib/-/issues/3094,
https://gitlab.gnome.org/GNOME/glib/-/issues/3095) and that
version will be uploaded to Debian unstable soon; but the change
is likely to be reinstated in a future version of GLib (see
https://gitlab.gnome.org/GNOME/glib/-/issues/3098).

    smcv