nixpkgs/pkgs/development/libraries/qt-5/5.5/qtbase/nix-profiles-library-paths.patch

Index: qt-everywhere-opensource-src-5.5.1/qtbase/src/corelib/kernel/qcoreapplication.cpp
===================================================================
--- qt-everywhere-opensource-src-5.5.1.orig/qtbase/src/corelib/kernel/qcoreapplication.cpp
+++ qt-everywhere-opensource-src-5.5.1/qtbase/src/corelib/kernel/qcoreapplication.cpp
@@ -2498,6 +2498,16 @@ QStringList QCoreApplication::libraryPat
                 }
             }
         }
+        qunsetenv("QT_PLUGIN_PATH"); // do not propagate to child processes
+
+        // Add library paths derived from NIX_PROFILES.
+        const QByteArrayList profiles = qgetenv("NIX_PROFILES").split(' ');
+        const QString plugindir = QString::fromLatin1("/lib/qt5/plugins");
+        Q_FOREACH (const QByteArray &profile, profiles) {
+            if (!profile.isEmpty()) {
+                app_libpaths->append(QFile::decodeName(profile) + plugindir);
+            }
+        }
     }
     return *(coreappdata()->app_libpaths);
 }