qt55: set QML import paths from NIX_PROFILES

pkgs/development/libraries/qt-5/5.5/default.nix

···
       /* qtandroidextras = not packaged */
       /* qtcanvas3d = not packaged */
       qtconnectivity = callPackage ./qtconnectivity.nix {};
-      qtdeclarative = callPackage ./qtdeclarative.nix {};
+      qtdeclarative = callPackage ./qtdeclarative {};
       qtdoc = callPackage ./qtdoc.nix {};
       qtenginio = callPackage ./qtenginio.nix {};
       qtgraphicaleffects = callPackage ./qtgraphicaleffects.nix {};

pkgs/development/libraries/qt-5/5.5/qtdeclarative.nix pkgs/development/libraries/qt-5/5.5/qtdeclarative/default.nix

···
 
 qtSubmodule {
   name = "qtdeclarative";
+  patches = [ ./0001-nix-profiles-import-paths.patch ];
   qtInputs = [ qtbase qtsvg qtxmlpatterns ];
   nativeBuildInputs = [ python ];
 }

pkgs/development/libraries/qt-5/5.5/qtdeclarative/0001-nix-profiles-import-paths.patch

···
+From 3f6fa74067aacd0e595e45b4ef7ce754514cb205 Mon Sep 17 00:00:00 2001
+From: Thomas Tuegel <[e-mail]>
+Date: Sat, 17 Oct 2015 09:28:18 -0500
+Subject: [PATCH] nix profiles import paths
+
+---
+ src/qml/qml/qqmlimport.cpp | 14 ++++++++++++++
+ 1 file changed, 14 insertions(+)
+
+diff --git a/src/qml/qml/qqmlimport.cpp b/src/qml/qml/qqmlimport.cpp
+index 5a54609..f33c2f9 100644
+--- a/src/qml/qml/qqmlimport.cpp
++++ b/src/qml/qml/qqmlimport.cpp
+@@ -1549,6 +1549,20 @@ QQmlImportDatabase::QQmlImportDatabase(QQmlEngine *e)
+     QString installImportsPath =  QLibraryInfo::location(QLibraryInfo::Qml2ImportsPath);
+     addImportPath(installImportsPath);
+ 
++    // Add import paths derived from NIX_PROFILES.
++    const QByteArray nixProfilesEnv = qgetenv("NIX_PROFILES");
++    if (!nixProfilesEnv.isEmpty()) {
++        QLatin1Char pathSep(' ');
++        QStringList paths = QFile::decodeName(nixProfilesEnv).split(pathSep, QString::SkipEmptyParts);
++        for (QStringList::iterator it = paths.begin(); it != paths.end(); ++it) {
++            it->append("/lib/qt5/qml");
++            QString canonicalPath = QDir(*it).canonicalPath();
++            if (!canonicalPath.isEmpty()) {
++                addImportPath(canonicalPath);
++            }
++        }
++    }
++
+     // env import paths
+     QByteArray envImportPath = qgetenv("QML2_IMPORT_PATH");
+     if (!envImportPath.isEmpty()) {
+-- 
+2.5.2
+