Cherry-pick godotengine#90431

Add `--import` command-line flag

editor/editor_file_system.h

@@ -304,6 +304,7 @@ class EditorFileSystem : public Node {
 	EditorFileSystemDirectory *get_filesystem();
 	bool is_scanning() const;
 	bool is_importing() const { return importing; }
+	bool doing_first_scan() const { return first_scan; }
 	float get_scanning_progress() const;
 	void scan();
 	void scan_changes();

main/main.cpp

@@ -89,6 +89,7 @@
 #include "editor/debugger/editor_debugger_node.h"
 #include "editor/doc_data_class_path.gen.h"
 #include "editor/doc_tools.h"
+#include "editor/editor_file_system.h"
 #include "editor/editor_help.h"
 #include "editor/editor_node.h"
 #include "editor/editor_paths.h"
@@ -179,6 +180,7 @@ static OS::ProcessID editor_pid = 0;
 static bool found_project = false;
 static bool auto_build_solutions = false;
 static String debug_server_uri;
+static bool wait_for_import = false;
 #ifndef DISABLE_DEPRECATED
 static int converter_max_kb_file = 4 * 1024; // 4MB
 static int converter_max_line_length = 100000;
@@ -505,6 +507,7 @@ void Main::print_help(const char *p_binary) {
 	OS::get_singleton()->print("  --main-loop <main_loop_name>      Run a MainLoop specified by its global class name.\n");
 	OS::get_singleton()->print("  --check-only                      Only parse for errors and quit (use with --script).\n");
 #ifdef TOOLS_ENABLED
+	OS::get_singleton()->print("--import                            Starts the editor, waits for any resources to be imported, and then quits.\n");
 	OS::get_singleton()->print("  --export-release <preset> <path>  Export the project in release mode using the given preset and output path. The preset name should match one defined in export_presets.cfg.\n");
 	OS::get_singleton()->print("                                    <path> should be absolute or relative to the project directory, and include the filename for the binary (e.g. 'builds/game.exe').\n");
 	OS::get_singleton()->print("                                    The target directory must exist.\n");
@@ -1288,12 +1291,17 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 				OS::get_singleton()->print("Missing file to load argument after --validate-extension-api, aborting.");
 				goto error;
 			}
-
+		} else if (I->get() == "--import") {
+			editor = true;
+			cmdline_tool = true;
+			wait_for_import = true;
+			quit_after = 1;
 		} else if (I->get() == "--export-release" || I->get() == "--export-debug" ||
 				I->get() == "--export-pack") { // Export project
 			// Actually handling is done in start().
 			editor = true;
 			cmdline_tool = true;
+			wait_for_import = true;
 			main_args.push_back(I->get());
 #ifndef DISABLE_DEPRECATED
 		} else if (I->get() == "--export") { // For users used to 3.x syntax.
@@ -3710,6 +3718,12 @@ bool Main::iteration() {
 		exit = true;
 	}
 
+#ifdef TOOLS_ENABLED
+	if (wait_for_import && EditorFileSystem::get_singleton()->doing_first_scan()) {
+		exit = false;
+	}
+#endif
+
 	if (fixed_fps != -1) {
 		return exit;
 	}