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.

1 files changed, 5 insertions, 3 deletions

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();