Add support for a QT_QUICK_CONTROLS_STYLE_PATH environment variable

[ChangeLog][Controls][Styles] Added support for a QT_QUICK_CONTROLS_STYLE_PATH
environment variable, which can be used to specify lookup paths for Qt
Quick Controls 2 styles. This allows device manufacturers and Linux
distributions to specify a system-wide style installation folder that
may be located outside the Qt installation tree.

Change-Id: Ic004d693bf6206971da6319d0cc13061b8fd1566
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

1 files changed, 10 insertions, 2 deletions

diff --git a/src/quickcontrols2/qquickstyle.cpp b/src/quickcontrols2/qquickstyle.cpp
index c8a3f19a..4247b204 100644
--- a/src/quickcontrols2/qquickstyle.cpp
+++ b/src/quickcontrols2/qquickstyle.cpp
@@ -182,6 +182,7 @@ struct QQuickStyleSpec
                 for (const QString &path : stylePaths) {
                     QString stylePath = findStyle(path, style);
                     if (!stylePath.isEmpty()) {
+                        custom = !stylePath.startsWith(baseUrl.toLocalFile());
                         style = stylePath;
                         resolved = true;
                         break;
@@ -212,15 +213,22 @@ Q_GLOBAL_STATIC(QQuickStyleSpec, styleSpec)
 
 QStringList QQuickStylePrivate::stylePaths()
 {
+    // system/custom style paths
+    QStringList paths;
+    if (Q_UNLIKELY(!qEnvironmentVariableIsEmpty("QT_QUICK_CONTROLS_STYLE_PATH"))) {
+        const QByteArray value = qgetenv("QT_QUICK_CONTROLS_STYLE_PATH");
+        paths += QString::fromLatin1(value).split(QDir::listSeparator(), QString::SkipEmptyParts);
+    }
+
+    // built-in import paths
     const QString targetPath = QStringLiteral("QtQuick/Controls.2");
     const QStringList importPaths = QQmlEngine().importPathList();
-
-    QStringList paths;
     for (const QString &importPath : importPaths) {
         QDir dir(importPath);
         if (dir.cd(targetPath))
             paths += dir.absolutePath();
     }
+
     return paths;
 }