Re: QT install and search paths

[Thomas Danckaert <post@thomasdanckaert.be>]

From: Hartmut Goebel <h.goebel@crazy-compilers.com>
Subject: QT install and search paths
Date: Wed, 23 Aug 2017 20:25:10 +0200

> [...] I found this in qt.scm
> (qtbase):
>
>            (search-path-specification
>             (variable "QT_PLUGIN_PATH")
>             (files '("plugins")))
>
> This means that `lib/plugins` is *not* included in QT_PLUGIN_PATH
> and thus not searched. (Which I assume is the reason for many
> test-failures.)

(indeed, e.g. for kdevplatform, I set the QT_PLUGIN_PATH before 
running tests)

> Also in qt.scm (qtbase) there is:
>
>                (substitute* qt_config.prf
>                   …
>                  (("\\$\\$\\[QT_INSTALL_PLUGINS\\]")
>                   "$$replace(dir, mkspecs/modules, plugins)")
>
> I assume this should make the plugins to be in stalled in …/plugins,
> but KDE framework is installing into …/lib/plugins.

I'm not sure if this is an error, or if KDE chooses this directory on 
purpose.

Either way, I think qtbase's QT_PLUGIN_PATH setting only has an 
effect if a user installs qtbase directly in their profile (or do I 
misunderstand native-search-paths?  The manual doesn't explain the 
difference between "native-search-paths" and "search-paths"), so 
applications using these plugins will still need to set the correct 
environment variable themselves somehow?

A previous discussion is here

https://lists.gnu.org/archive/html/guix-devel/2016-12/msg00776.html

For the kdevelop package, I wrapped the executable, setting a bunch 
of Qt-related environment variables.  This works as a stop-gap, but 
it will break down when a user uses multiple Qt/KDE applications with 
different plugin requirements (some KDE daemons, such as kdeinit, 
need to find all their plugins at the moment they are started).

Ludo suggested using a profile hook to set the required environment 
variables depending on the installed applications, but I never looked 
into it further because wrapping the executable was “good enough” 
for.  For a KDE desktop, I think you'll need a better solution.

Thomas