[macOS] Add option to emit signal when opening files/urls with the app, instead of starting new instance.

core/config/project_settings.cpp

@@ -1446,6 +1446,7 @@ ProjectSettings::ProjectSettings() {
 	GLOBAL_DEF("application/run/main_loop_type", "SceneTree");
 	GLOBAL_DEF("application/config/auto_accept_quit", true);
 	GLOBAL_DEF("application/config/quit_on_go_back", true);
+	GLOBAL_DEF_BASIC("application/config/emit_on_file_open", false);
 
 	// The default window size is tuned to:
 	// - Have a 16:9 aspect ratio,

core/os/main_loop.cpp

@@ -45,6 +45,7 @@ void MainLoop::_bind_methods() {
 	BIND_CONSTANT(NOTIFICATION_TEXT_SERVER_CHANGED);
 
 	ADD_SIGNAL(MethodInfo("on_request_permissions_result", PropertyInfo(Variant::STRING, "permission"), PropertyInfo(Variant::BOOL, "granted")));
+	ADD_SIGNAL(MethodInfo("on_file_open", PropertyInfo(Variant::PACKED_STRING_ARRAY, "files")));
 
 	GDVIRTUAL_BIND(_initialize);
 	GDVIRTUAL_BIND(_physics_process, "delta");

doc/classes/MainLoop.xml

@@ -90,6 +90,13 @@
 		</method>
 	</methods>
 	<signals>
+		<signal name="on_file_open">
+			<param index="0" name="files" type="PackedStringArray" />
+			<description>
+				Emitted when a user opens file with the application. Signal is emitted only is [member ProjectSettings.application/config/emit_on_file_open] is [code]true[/code] or application is running in the macOS sandbox.
+				[b]Note:[/b] This signal is implemented only on macOS.
+			</description>
+		</signal>
 		<signal name="on_request_permissions_result">
 			<param index="0" name="permission" type="String" />
 			<param index="1" name="granted" type="bool" />

doc/classes/ProjectSettings.xml

@@ -276,6 +276,10 @@
 		<member name="application/config/description" type="String" setter="" getter="" default="&quot;&quot;">
 			The project's description, displayed as a tooltip in the Project Manager when hovering the project.
 		</member>
+		<member name="application/config/emit_on_file_open" type="bool" setter="" getter="" default="false">
+			If [code]true[/code], application will emit [signal MainLoop.on_file_open] signal instead of starting new application instance.
+			[b]Note:[/b] This setting is implemented only on macOS.
+		</member>
 		<member name="application/config/icon" type="String" setter="" getter="" default="&quot;&quot;">
 			Icon used for the project, set when project loads. Exporters will also use this icon as a fallback if necessary.
 		</member>

platform/macos/godot_application_delegate.mm

@@ -179,8 +179,16 @@
 
 	if (!args.is_empty()) {
 		if (os->get_main_loop()) {
-			// Application is already running, open a new instance with the URL/files as command line arguments.
+			// Application is already running, open a new instance with the URL/files as command line arguments, or emit signal.
+			if ((OS::get_singleton()->is_sandboxed() || GLOBAL_GET("application/config/emit_on_file_open").operator bool()) && !Engine::get_singleton()->is_editor_hint()) {
+				Vector<String> args_vector;
+				for (List<String>::Element *E = args.front(); E; E = E->next()) {
+					args_vector.push_back(E->get());
+				}
+				os->get_main_loop()->emit_signal(SNAME("on_file_open"), args_vector);
+			} else {
 				os->create_instance(args);
+			}
 		} else {
 			// Application is just started, add to the list of command line arguments and continue.
 			os->set_cmdline_platform_args(args);