bug#45193: [PATCH 2/4] guix: qt-utils: Wrapped executables honor user's envvars.

[Hartmut Goebel]

Prior to this change, wrappers did set the specified environment variables to
a fixed value, overwriting any user settings. This inhibited propagating
e.g. XDG_DATA_DIRS from a profile to the application.

Now user environment variables are prefixed (if the variable defines some
"binary" search path, e.g. QT_PLUGIN_PATH) or suffixed (if the variable
defines some config or data search path, e.g. XDG_DATA_DIRS). The code could
also allow to overwrite, anyhow currently no variable is defined like this.

* guix/build/qt-utils.scm (variables-for-wrapping): For each env-var to
  be wrapped, specify whether it should prefix, suffix or overwrite the
  user's variable.
---
 guix/build/qt-utils.scm | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/guix/build/qt-utils.scm b/guix/build/qt-utils.scm
index 3fbdb6be61..030059522d 100644
--- a/guix/build/qt-utils.scm
+++ b/guix/build/qt-utils.scm
@@ -39,14 +39,15 @@
    (lambda (var-to-wrap) (not (null? (last var-to-wrap))))
    (map
     (lambda (var-spec)
-      `(,(first var-spec) = ,(collect-sub-dirs base-directories (last 
var-spec))))
+      (list (first var-spec) (second var-spec)
+            (collect-sub-dirs base-directories (third var-spec))))
     (list
      ;; these shall match the search-path-specification for Qt and KDE
      ;; libraries
-     '("XDG_DATA_DIRS" "/share")
-     '("XDG_CONFIG_DIRS" "/etc/xdg")
-     '("QT_PLUGIN_PATH" "/lib/qt5/plugins")
-     '("QML2_IMPORT_PATH" "/lib/qt5/qml")))))
+     '("XDG_DATA_DIRS" suffix "/share")
+     '("XDG_CONFIG_DIRS" suffix "/etc/xdg")
+     '("QT_PLUGIN_PATH" prefix "/lib/qt5/plugins")
+     '("QML2_IMPORT_PATH" prefix "/lib/qt5/qml")))))
 
 
 (define* (wrap-qt-program* program #:key inputs output-dir)
-- 
2.21.3