Add `_get_unsaved_status()` method to EditorPlugin

doc/classes/EditorPlugin.xml

@@ -280,6 +280,22 @@
 				[/codeblock]
 			</description>
 		</method>
+		<method name="_get_unsaved_status" qualifiers="virtual const">
+			<return type="String" />
+			<description>
+				Override this method to provide a custom message that lists unsaved changes. The editor will call this method on exit and display it in a confirmation dialog. Return empty string if the plugin has no unsaved changes.
+				If the user confirms saving, [method _save_external_data] will be called, before closing the editor.
+				[codeblock]
+				func _get_unsaved_status():
+				    if unsaved:
+				        return "Save changes in MyCustomPlugin before closing?"
+				    return ""
+				
+				func _save_external_data():
+				    unsaved = false
+				[/codeblock]
+			</description>
+		</method>
 		<method name="_get_window_layout" qualifiers="virtual">
 			<return type="void" />
 			<param index="0" name="configuration" type="ConfigFile" />

editor/editor_node.cpp

@@ -2777,6 +2777,11 @@ void EditorNode::_menu_option_confirm(int p_option, bool p_confirmed) {
 		case FILE_QUIT:
 		case RUN_PROJECT_MANAGER:
 		case RELOAD_CURRENT_PROJECT: {
+			if (p_confirmed && plugin_to_save) {
+				plugin_to_save->save_external_data();
+				p_confirmed = false;
+			}
+
 			if (!p_confirmed) {
 				bool save_each = EDITOR_GET("interface/editor/save_each_scene_on_quit");
 				if (_next_unsaved_scene(!save_each) == -1) {
@@ -2792,6 +2797,27 @@ void EditorNode::_menu_option_confirm(int p_option, bool p_confirmed) {
 						save_confirmation->popup_centered();
 						break;
 					}
+					
+					plugin_to_save = nullptr;
+					for (int i = 0; i < editor_data.get_editor_plugin_count(); i++) {
+						const String unsaved_status = editor_data.get_editor_plugin(i)->get_unsaved_status();
+						if (!unsaved_status.is_empty()) {
+							if (p_option == RELOAD_CURRENT_PROJECT) {
+								save_confirmation->set_ok_button_text(TTR("Save & Reload"));
+								save_confirmation->set_text(RTR(unsaved_status));
+							} else {
+								save_confirmation->set_ok_button_text(TTR("Save & Quit"));
+								save_confirmation->set_text(RTR(unsaved_status));
+							}
+							save_confirmation->popup_centered();
+							plugin_to_save = editor_data.get_editor_plugin(i);
+							break;
+						}
+					}
+					
+					if (plugin_to_save) {
+						break;
+					}
 
 					_discard_changes();
 					break;

editor/editor_node.h

@@ -382,6 +382,7 @@ private:
 	AcceptDialog *save_accept = nullptr;
 	EditorAbout *about = nullptr;
 	AcceptDialog *warning = nullptr;
+	EditorPlugin *plugin_to_save = nullptr;
 
 	int overridden_default_layout = -1;
 	Ref<ConfigFile> default_layout;

editor/editor_plugin.cpp

@@ -341,7 +341,12 @@ void EditorPlugin::clear() {
 	GDVIRTUAL_CALL(_clear);
 }
 
-// if editor references external resources/scenes, save them
+String EditorPlugin::get_unsaved_status() const {
+	String ret;
+	GDVIRTUAL_CALL(_get_unsaved_status, ret);
+	return ret;
+}
+
 void EditorPlugin::save_external_data() {
 	GDVIRTUAL_CALL(_save_external_data);
 }
@@ -594,6 +599,7 @@ void EditorPlugin::_bind_methods() {
 	GDVIRTUAL_BIND(_get_state);
 	GDVIRTUAL_BIND(_set_state, "state");
 	GDVIRTUAL_BIND(_clear);
+	GDVIRTUAL_BIND(_get_unsaved_status);
 	GDVIRTUAL_BIND(_save_external_data);
 	GDVIRTUAL_BIND(_apply_changes);
 	GDVIRTUAL_BIND(_get_breakpoints);

editor/editor_plugin.h

@@ -88,6 +88,7 @@ protected:
 	GDVIRTUAL0RC(Dictionary, _get_state)
 	GDVIRTUAL1(_set_state, Dictionary)
 	GDVIRTUAL0(_clear)
+	GDVIRTUAL0RC(String, _get_unsaved_status)
 	GDVIRTUAL0(_save_external_data)
 	GDVIRTUAL0(_apply_changes)
 	GDVIRTUAL0RC(Vector<String>, _get_breakpoints)
@@ -175,6 +176,7 @@ public:
 	virtual Dictionary get_state() const; //save editor state so it can't be reloaded when reloading scene
 	virtual void set_state(const Dictionary &p_state); //restore editor state (likely was saved with the scene)
 	virtual void clear(); // clear any temporary data in the editor, reset it (likely new scene or load another scene)
+	virtual String get_unsaved_status() const;
 	virtual void save_external_data(); // if editor references external resources/scenes, save them
 	virtual void apply_changes(); // if changes are pending in editor, apply them
 	virtual void get_breakpoints(List<String> *p_breakpoints);