bug#57742: QT plugins from profile not found (QT_PLUGIN_PATH)

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

[re-sending again, this time with debbugs in CC]

Hello,

Morgan Smith <Morgan.J.Smith@outlook.com> writes:

> Hello!
>
> Ever since commit 1f466ed6be932526fc69e72ffd50390691d0d382 we don't look
> at the user's value of QT_PLUGIN_PATH.  The comment says this is to
> prevent plugin confusion between Qt5 and Qt6 stuff.

Yes; unfortunately Qt doesn't seem to have thought about making that
variable usable with both Qt5 and Qt6 at the same time.  It's probably
worth reporting the issue upstream.

> This is very unfortunate for me.  I have qtwayland (qt5) installed in my
> profile so QT programs can find the wayland plugin they need to display
> themselves on wayland.  Unfortunately, they no longer can.

I see.

> Maybe we could make our own Guix environment variables like
> GUIX_QT5_QT_PLUGIN_PATH and GUIX_QT6_QT_PLUGIN_PATH and then add those
> to the wrapper?  So like qtwayland would set GUIX_QT5_QT_PLUGIN_PATH and
> then the wrapper in qt-utils.scm could read that?  Just an idea, I have
> no clue what a good solution for this issue looks like.

That could work for qt-build-system built packages, yes.  We could also
attempt to patch our Qt packages to honor these directly, if that's not
too difficult.  Then straightforward search paths could be defined for
them, and the wrapper in qt-utils adjusted.

Thanks,

Maxim