Test required params/returns (currently UB)

Author: Bromeon

godot-codegen/src/lib.rs

@@ -52,7 +52,15 @@ pub const IS_CODEGEN_FULL: bool = false;
 pub const IS_CODEGEN_FULL: bool = true;
 
 #[cfg(all(feature = "experimental-required-objs", before_api = "4.6"))]
-compile_error!("The `experimental-required-objs` feature needs at least Godot 4.6-dev version");
+fn __feature_warning() {
+    // Not a hard error, it's experimental anyway and allows more flexibility like this.
+    #[must_use = "The `experimental-required-objs` feature needs at least Godot 4.6-dev version"]
+    fn feature_has_no_effect() -> i32 {
+        1
+    }
+
+    feature_has_no_effect();
+}
 
 fn write_file(path: &Path, contents: String) {
     let dir = path.parent().unwrap();

itest/rust/Cargo.toml

@@ -13,7 +13,7 @@ crate-type = ["cdylib"]
 # Default feature MUST be empty for workflow reasons, even if it differs from the default feature set in upstream `godot` crate.
 default = []
 codegen-full = ["godot/__codegen-full"]
-codegen-full-experimental = ["codegen-full", "godot/experimental-godot-api"]
+codegen-full-experimental = ["codegen-full", "godot/experimental-godot-api", "godot/experimental-required-objs"]
 experimental-threads = ["godot/experimental-threads"]
 register-docs = ["godot/register-docs"]
 serde = ["dep:serde", "dep:serde_json", "godot/serde"]

itest/rust/src/engine_tests/node_test.rs

@@ -74,3 +74,25 @@ fn node_call_group(ctx: &TestContext) {
     tree.call_group("group", "remove_meta", vslice!["something"]);
     assert!(!node.has_meta("something"));
 }
+
+// Experimental required parameter/return value: https://github.com/godot-rust/gdext/pull/1383.
+#[cfg(all(feature = "codegen-full-experimental", since_api = "4.6"))]
+#[itest(focus)]
+fn node_required_param_return() {
+    use godot::classes::Tween;
+    use godot::obj::Gd;
+
+    let mut parent = Node::new_alloc();
+    let child = Node::new_alloc();
+
+    // add_child() takes required arg, so this still works.
+    // (Test for Option *not* working anymore is in godot > no_compile_tests.)
+    parent.add_child(&child);
+
+    // create_tween() returns now non-null instance.
+    let tween: Gd<Tween> = parent.create_tween();
+    assert!(tween.is_instance_valid());
+    assert!(tween.to_string().contains("Tween"));
+
+    parent.free();
+}