Use Jolt Physics by default in newly created projects

This also adds infrastructure to make specific settings the default, but only
in projects created after this point (so that existing projects
are not affected). This can be used for progressive upgrades in the future.

This applies to both the project creation dialog and creating projects
through the command line using `touch project.godot`.

doc/classes/ProjectSettings.xml

@@ -2527,7 +2527,7 @@
 			Sets which physics engine to use for 3D physics.
 			[b]DEFAULT[/b] is currently equivalent to [b]GodotPhysics3D[/b], but may change in future releases. Select an explicit implementation if you want to ensure that your project stays on the same engine.
 			[b]GodotPhysics3D[/b] is Godot's internal 3D physics engine.
-			[b]Jolt Physics[/b] is an alternative physics engine that is generally faster and more reliable than [b]GodotPhysics3D[/b]. As it was recently implemented, it is currently considered experimental and its behavior may change in future releases.
+			[b]Jolt Physics[/b] is an alternative physics engine that is generally faster and more reliable than [b]GodotPhysics3D[/b]. As it was recently implemented, it is currently considered experimental and its behavior may change in future releases. Jolt Physics is the default for projects created starting in Godot 4.6.
 			[b]Dummy[/b] is a 3D physics server that does nothing and returns only dummy values, effectively disabling all 3D physics functionality.
 			Third-party extensions and modules can add other physics engines to select with this setting.
 		</member>

editor/editor_node.cpp

@@ -907,7 +907,17 @@ void EditorNode::_notification(int p_what) {
 			feature_profile_manager->notify_changed();
 
 			// Save the project after opening to mark it as last modified, except in headless mode.
+			// Also use this opportunity to ensure default settings are applied to new projects created from the command line
+			// using `touch project.godot`.
 			if (DisplayServer::get_singleton()->window_can_draw()) {
+				const String project_settings_path = ProjectSettings::get_singleton()->get_resource_path().path_join("project.godot");
+				// Check the file's size in bytes as an optimization. If it's under 10 bytes, the file is assumed to be empty.
+				if (FileAccess::get_size(project_settings_path) < 10) {
+					const HashMap<String, Variant> initial_settings = get_initial_settings();
+					for (const KeyValue<String, Variant> &initial_setting : initial_settings) {
+						ProjectSettings::get_singleton()->set_setting(initial_setting.key, initial_setting.value);
+					}
+				}
 				ProjectSettings::get_singleton()->save();
 			}
 
@@ -7528,6 +7538,17 @@ void EditorNode::notify_settings_overrides_changed() {
 	settings_overrides_changed = true;
 }
 
+// Returns the list of project settings to add to new projects. This is used by the
+// project manager creation dialog, but also applies to empty `project.godot` files
+// to cover the command line workflow of creating projects using `touch project.godot`.
+//
+// This is used to set better defaults for new projects without affecting existing projects.
+HashMap<String, Variant> EditorNode::get_initial_settings() {
+	HashMap<String, Variant> settings;
+	settings["physics/3d/physics_engine"] = "Jolt Physics";
+	return settings;
+}
+
 EditorNode::EditorNode() {
 	DEV_ASSERT(!singleton);
 	singleton = this;

editor/editor_node.h

@@ -768,6 +768,9 @@ public:
 	static bool immediate_confirmation_dialog(const String &p_text, const String &p_ok_text = TTR("Ok"), const String &p_cancel_text = TTR("Cancel"), uint32_t p_wrap_width = 0);
 
 	static bool is_cmdline_mode();
+
+	static HashMap<String, Variant> get_initial_settings();
+
 	static void cleanup();
 
 	EditorPluginList *get_editor_plugins_force_input_forwarding() { return editor_plugins_force_input_forwarding; }

editor/project_manager/project_dialog.cpp

@@ -34,6 +34,7 @@
 #include "core/io/dir_access.h"
 #include "core/io/zip_io.h"
 #include "core/version.h"
+#include "editor/editor_node.h"
 #include "editor/editor_string_names.h"
 #include "editor/gui/editor_file_dialog.h"
 #include "editor/settings/editor_settings.h"
@@ -545,6 +546,11 @@ void ProjectDialog::ok_pressed() {
 		initial_settings["application/config/features"] = project_features;
 		initial_settings["application/config/name"] = project_name->get_text().strip_edges();
 		initial_settings["application/config/icon"] = "res://icon.svg";
+		ProjectSettings::CustomMap extra_settings = EditorNode::get_initial_settings();
+		for (const KeyValue<String, Variant> &extra_setting : extra_settings) {
+			// Merge with other initial settings defined above.
+			initial_settings[extra_setting.key] = extra_setting.value;
+		}
 
 		Error err = ProjectSettings::get_singleton()->save_custom(path.path_join("project.godot"), initial_settings, Vector<String>(), false);
 		if (err != OK) {