Refactor OS exit code to be `EXIT_SUCCESS` by default

- `Main::setup` early exits (failure or `--help`/`--version`) now
  consistently return `EXIT_FAILURE` or `EXIT_SUCCESS` on all platforms,
  instead of 255 on some and a Godot Error code on others.
- `Main::start` now returns the exit code, simplifying the handling of early
  failures.
- `Main::iteration` needs to explicit set the exit code in OS if it errors
  out.
- Web and iOS now properly return `OS::get_exit_code()` instead of 0.

5 files changed, 36 insertions, 31 deletions

diff --git a/platform/ios/godot_ios.mm b/platform/ios/godot_ios.mm
index 5e66c8b47b..9d35d43344 100644
--- a/platform/ios/godot_ios.mm
+++ b/platform/ios/godot_ios.mm
@@ -102,15 +102,16 @@ int ios_main(int argc, char **argv) {
 
 	Error err = Main::setup(fargv[0], argc - 1, &fargv[1], false);
 
-	if (err == ERR_HELP) { // Returned by --help and --version, so success.
-		return 0;
-	} else if (err != OK) {
-		return 255;
+	if (err != OK) {
+		if (err == ERR_HELP) { // Returned by --help and --version, so success.
+			return EXIT_SUCCESS;
+		}
+		return EXIT_FAILURE;
 	}
 
 	os->initialize_modules();
 
-	return 0;
+	return os->get_exit_code();
 }
 
 void ios_finish() {
diff --git a/platform/linuxbsd/godot_linuxbsd.cpp b/platform/linuxbsd/godot_linuxbsd.cpp
index a2b6fbeb25..b0880c86b8 100644
--- a/platform/linuxbsd/godot_linuxbsd.cpp
+++ b/platform/linuxbsd/godot_linuxbsd.cpp
@@ -72,18 +72,19 @@ int main(int argc, char *argv[]) {
 	char *ret = getcwd(cwd, PATH_MAX);
 
 	Error err = Main::setup(argv[0], argc - 1, &argv[1]);
+
 	if (err != OK) {
 		free(cwd);
-
 		if (err == ERR_HELP) { // Returned by --help and --version, so success.
-			return 0;
+			return EXIT_SUCCESS;
 		}
-		return 255;
+		return EXIT_FAILURE;
 	}
 
-	if (Main::start()) {
-		os.set_exit_code(EXIT_SUCCESS);
-		os.run(); // it is actually the OS that decides how to run
+	if (Main::start() == EXIT_SUCCESS) {
+		os.run();
+	} else {
+		os.set_exit_code(EXIT_FAILURE);
 	}
 	Main::cleanup();
 
diff --git a/platform/macos/godot_main_macos.mm b/platform/macos/godot_main_macos.mm
index 3959fb686c..279d805462 100644
--- a/platform/macos/godot_main_macos.mm
+++ b/platform/macos/godot_main_macos.mm
@@ -69,18 +69,21 @@ int main(int argc, char **argv) {
 		err = Main::setup(argv[0], argc - first_arg, &argv[first_arg]);
 	}
 
-	if (err == ERR_HELP) { // Returned by --help and --version, so success.
-		return 0;
-	} else if (err != OK) {
-		return 255;
+	if (err != OK) {
+		if (err == ERR_HELP) { // Returned by --help and --version, so success.
+			return EXIT_SUCCESS;
+		}
+		return EXIT_FAILURE;
 	}
 
-	bool ok;
+	int ret;
 	@autoreleasepool {
-		ok = Main::start();
+		ret = Main::start();
 	}
-	if (ok) {
-		os.run(); // It is actually the OS that decides how to run.
+	if (ret) {
+		os.run();
+	} else {
+		os.set_exit_code(EXIT_FAILURE);
 	}
 
 	@autoreleasepool {
diff --git a/platform/web/web_main.cpp b/platform/web/web_main.cpp
index ad2a801881..04513f6d57 100644
--- a/platform/web/web_main.cpp
+++ b/platform/web/web_main.cpp
@@ -109,24 +109,22 @@ extern EMSCRIPTEN_KEEPALIVE int godot_web_main(int argc, char *argv[]) {
 
 	// Proper shutdown in case of setup failure.
 	if (err != OK) {
-		int exit_code = (int)err;
-		if (err == ERR_HELP) {
-			exit_code = 0; // Called with --help.
-		}
-		os->set_exit_code(exit_code);
 		// Will only exit after sync.
 		emscripten_set_main_loop(exit_callback, -1, false);
 		godot_js_os_finish_async(cleanup_after_sync);
-		return exit_code;
+		if (err == ERR_HELP) { // Returned by --help and --version, so success.
+			return EXIT_SUCCESS;
+		}
+		return EXIT_FAILURE;
 	}
 
-	os->set_exit_code(0);
 	main_started = true;
 
 	// Ease up compatibility.
 	ResourceLoader::set_abort_on_missing_resources(false);
 
-	Main::start();
+	int ret = Main::start();
+	os->set_exit_code(ret);
 	os->get_main_loop()->initialize();
 #ifdef TOOLS_ENABLED
 	if (Engine::get_singleton()->is_project_manager_hint() && FileAccess::exists("/tmp/preload.zip")) {
@@ -140,5 +138,5 @@ extern EMSCRIPTEN_KEEPALIVE int godot_web_main(int argc, char *argv[]) {
 	// We are inside an animation frame, we want to immediately draw on the newly setup canvas.
 	main_loop_callback();
 
-	return 0;
+	return os->get_exit_code();
 }
diff --git a/platform/windows/godot_windows.cpp b/platform/windows/godot_windows.cpp
index f86ecd87fb..5f41b4e568 100644
--- a/platform/windows/godot_windows.cpp
+++ b/platform/windows/godot_windows.cpp
@@ -171,13 +171,15 @@ int widechar_main(int argc, wchar_t **argv) {
 		delete[] argv_utf8;
 
 		if (err == ERR_HELP) { // Returned by --help and --version, so success.
-			return 0;
+			return EXIT_SUCCESS;
 		}
-		return 255;
+		return EXIT_FAILURE;
 	}
 
-	if (Main::start()) {
+	if (Main::start() == EXIT_SUCCESS) {
 		os.run();
+	} else {
+		os.set_exit_code(EXIT_FAILURE);
 	}
 	Main::cleanup();