Gui: Try to load Theme Parameters from file

This creates logic that tries to load user parameters from file as the
priority and pushes back older mechanism to lower layer. Older way of
loading theme parameters should be preserved until we release first 1.1
RC.

src/Gui/Application.cpp

@@ -141,6 +141,7 @@
 #include "QtWidgets.h"
 
 #include <OverlayManager.h>
+#include <ParamHandler.h>
 #include <Base/ServiceProvider.h>
 
 #ifdef BUILD_TRACY_FRAME_PROFILER
@@ -381,20 +382,48 @@ struct PyMethodDef FreeCADGui_methods[] = {
 
 void Application::initStyleParameterManager()
 {
+    static ParamHandlers handlers;
+
+    const auto deduceParametersFilePath = []() -> std::string {
+        const auto hMainWindowGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/MainWindow");
+
+        if (const std::string& path = hMainWindowGrp->GetASCII("ThemeStyleParametersFile");
+            !path.empty()) {
+            return path;
+        }
+
+        return fmt::format("qss:parameters/{}.yaml", hMainWindowGrp->GetASCII("Theme", "Classic"));
+    };
+
+    auto themeParametersSource = new StyleParameters::YamlParameterSource(
+        deduceParametersFilePath(),
+        {.name = QT_TR_NOOP("Theme Parameters"),
+         .options = StyleParameters::ParameterSourceOption::UserEditable});
+
+    handlers.addDelayedHandler(
+        "BaseApp/Preferences/MainWindow",
+        {"ThemeStyleParametersFiles", "Theme"},
+        [themeParametersSource, deduceParametersFilePath](ParameterGrp::handle) {
+            themeParametersSource->changeFilePath(deduceParametersFilePath());
+        });
+
     Base::registerServiceImplementation<StyleParameters::ParameterSource>(
         new StyleParameters::BuiltInParameterSource({.name = QT_TR_NOOP("Built-in Parameters")}));
 
-    Base::registerServiceImplementation<StyleParameters::ParameterSource>(
-        new StyleParameters::UserParameterSource(
-            App::GetApplication().GetParameterGroupByPath(
-                "User parameter:BaseApp/Preferences/Themes/Tokens"),
-            {.name = QT_TR_NOOP("Theme Parameters"),
-             .options = StyleParameters::ParameterSourceOption::UserEditable}));
-
+    // todo: left for compatibility with older theme versions, to be removed before release
     Base::registerServiceImplementation<StyleParameters::ParameterSource>(
         new StyleParameters::UserParameterSource(
             App::GetApplication().GetParameterGroupByPath(
                 "User parameter:BaseApp/Preferences/Themes/UserTokens"),
+            {.name = QT_TR_NOOP("Theme Parameters - Fallback"),
+             .options = StyleParameters::ParameterSourceOption::ReadOnly}));
+
+    Base::registerServiceImplementation<StyleParameters::ParameterSource>(themeParametersSource);
+
+    Base::registerServiceImplementation<StyleParameters::ParameterSource>(
+        new StyleParameters::UserParameterSource(
+            App::GetApplication().GetParameterGroupByPath(
+                "User parameter:BaseApp/Preferences/Themes/UserParameters"),
             {.name = QT_TR_NOOP("User Parameters"),
              .options = StyleParameters::ParameterSource::UserEditable}));
 

src/Gui/StyleParameters/ParameterManager.cpp

@@ -223,7 +223,17 @@ void UserParameterSource::remove(const std::string& name)
 
 YamlParameterSource::YamlParameterSource(const std::string& filePath, const Metadata& metadata)
     : ParameterSource(metadata)
-    , filePath(filePath)
+{
+    changeFilePath(filePath);
+}
+
+void YamlParameterSource::changeFilePath(const std::string& path)
+{
+    this->filePath = path;
+    reload();
+}
+
+void YamlParameterSource::reload()
 {
     QFile file(QString::fromStdString(filePath));
 
@@ -240,6 +250,7 @@ YamlParameterSource::YamlParameterSource(const std::string& filePath, const Meta
     std::string content = in.readAll().toStdString();
 
     YAML::Node root = YAML::Load(content);
+    parameters.clear();
     for (auto it = root.begin(); it != root.end(); ++it) {
         auto key = it->first.as<std::string>();
         auto value = it->second.as<std::string>();
@@ -288,7 +299,7 @@ void YamlParameterSource::flush()
 
     QFile file(QString::fromStdString(filePath));
     if (!file.open(QIODevice::WriteOnly | QIODevice::Truncate | QIODevice::Text)) {
-        FC_TRACE("StyleParameters: Unable to open file " << filePath);
+        FC_WARN("StyleParameters: Unable to open file " << filePath);
         return;
     }
 

src/Gui/StyleParameters/ParameterManager.h

@@ -403,6 +403,9 @@ public:
      */
     explicit YamlParameterSource(const std::string& filePath, const Metadata& metadata = {});
 
+    void changeFilePath(const std::string& path);
+    void reload();
+
     std::list<Parameter> all() const override;
     std::optional<Parameter> get(const std::string& name) const override;
     void define(const Parameter& param) override;