Implement the `%command%` placeholder in the Main Run Args setting

This can be used to tell Godot to run an executable that will run Godot
rather than running Godot directly. This is useful to make Godot start
on the dedicated GPU when using a NVIDIA Optimus setup on Linux:
`prime-run %command%`

The `editor/run/main_run_args` setting declaration was moved to make it
visible in the ProjectSettings documentation.

2 files changed, 40 insertions, 7 deletions

diff --git a/editor/editor_node.cpp b/editor/editor_node.cpp
index ed670b1296..07e95e7b83 100644
--- a/editor/editor_node.cpp
+++ b/editor/editor_node.cpp
@@ -5877,8 +5877,6 @@ EditorNode::EditorNode() {
 
 	register_exporters();
 
-	GLOBAL_DEF("editor/run/main_run_args", "");
-
 	ClassDB::set_class_enabled("RootMotionView", true);
 
 	//defs here, use EDITOR_GET in logic
diff --git a/editor/editor_run.cpp b/editor/editor_run.cpp
index e46f4eb65a..5e6d2ab69c 100644
--- a/editor/editor_run.cpp
+++ b/editor/editor_run.cpp
@@ -183,15 +183,50 @@ Error EditorRun::run(const String &p_scene, const String &p_custom_args, const L
 		args.push_back(p_scene);
 	}
 
+	String exec = OS::get_singleton()->get_executable_path();
+
 	if (p_custom_args != "") {
-		Vector<String> cargs = p_custom_args.split(" ", false);
-		for (int i = 0; i < cargs.size(); i++) {
-			args.push_back(cargs[i].replace(" ", "%20"));
+		// Allow the user to specify a command to run, similar to Steam's launch options.
+		// In this case, Godot will no longer be run directly; it's up to the underlying command
+		// to run it. For instance, this can be used on Linux to force a running project
+		// to use Optimus using `prime-run` or similar.
+		// Example: `prime-run %command% --time-scale 0.5`
+		const int placeholder_pos = p_custom_args.find("%command%");
+
+		Vector<String> custom_args;
+
+		if (placeholder_pos != -1) {
+			// Prepend executable-specific custom arguments.
+			// If nothing is placed before `%command%`, behave as if no placeholder was specified.
+			Vector<String> exec_args = p_custom_args.substr(0, placeholder_pos).split(" ", false);
+			if (exec_args.size() >= 1) {
+				exec = exec_args[0];
+				exec_args.remove(0);
+
+				// Append the Godot executable name before we append executable arguments
+				// (since the order is reversed when using `push_front()`).
+				args.push_front(OS::get_singleton()->get_executable_path());
+			}
+
+			for (int i = exec_args.size() - 1; i >= 0; i--) {
+				// Iterate backwards as we're pushing items in the reverse order.
+				args.push_front(exec_args[i].replace(" ", "%20"));
+			}
+
+			// Append Godot-specific custom arguments.
+			custom_args = p_custom_args.substr(placeholder_pos + String("%command%").size()).split(" ", false);
+			for (int i = 0; i < custom_args.size(); i++) {
+				args.push_back(custom_args[i].replace(" ", "%20"));
+			}
+		} else {
+			// Append Godot-specific custom arguments.
+			custom_args = p_custom_args.split(" ", false);
+			for (int i = 0; i < custom_args.size(); i++) {
+				args.push_back(custom_args[i].replace(" ", "%20"));
+			}
 		}
 	}
 
-	String exec = OS::get_singleton()->get_executable_path();
-
 	printf("Running: %s", exec.utf8().get_data());
 	for (List<String>::Element *E = args.front(); E; E = E->next()) {
 		printf(" %s", E->get().utf8().get_data());