Add ParamType::arg_into_owned() for generic arg->value conversion

Author: Bromeon

godot-core/src/builtin/collections/array.rs

@@ -1137,6 +1137,10 @@ impl<T: ArrayElement> ParamType for Array<T> {
     fn arg_to_ref<'r>(arg: &'r Self::Arg<'_>) -> &'r Self {
         arg.cow_as_ref()
     }
+
+    fn arg_into_owned(arg: Self::Arg<'_>) -> Self {
+        arg.cow_into_owned()
+    }
 }
 
 impl<T: ArrayElement> GodotConvert for Array<T> {

godot-core/src/meta/args/as_arg.rs

@@ -90,9 +90,17 @@ macro_rules! arg_into_ref {
 #[macro_export]
 macro_rules! arg_into_owned {
     ($arg_variable:ident) => {
+        // Non-generic version allows type inference. Only applicable for CowArg types.
         let $arg_variable = $arg_variable.into_arg();
         let $arg_variable = $arg_variable.cow_into_owned();
-        // cow_into_owned() is not yet used generically; could be abstracted in ParamType::arg_to_owned() as well.
+    };
+    ($arg_variable:ident: $T:ty) => {
+        let $arg_variable = $arg_variable.into_arg();
+        let $arg_variable: $T = $crate::meta::ParamType::arg_into_owned($arg_variable);
+    };
+    (infer $arg_variable:ident) => {
+        let $arg_variable = $arg_variable.into_arg();
+        let $arg_variable = $crate::meta::ParamType::arg_into_owned($arg_variable);
     };
 }
 
@@ -116,6 +124,10 @@ macro_rules! impl_asarg_by_value {
             fn arg_to_ref<'r>(arg: &'r Self::Arg<'_>) -> &'r Self {
                 arg
             }
+
+            fn arg_into_owned(arg: Self::Arg<'_>) -> Self {
+                arg
+            }
         }
     };
 }
@@ -149,6 +161,10 @@ macro_rules! impl_asarg_by_ref {
             fn arg_to_ref<'r>(arg: &'r Self::Arg<'_>) -> &'r Self {
                 arg.cow_as_ref()
             }
+
+            fn arg_into_owned(arg: Self::Arg<'_>) -> Self {
+                arg.cow_into_owned()
+            }
         }
     };
 }
@@ -280,4 +296,10 @@ pub trait ParamType: sealed::Sealed + Sized + 'static
     /// Useful in generic contexts where you need to extract a reference of an argument, independently of how it is passed.
     #[doc(hidden)] // for now, users are encouraged to use only call-site of impl AsArg; declaration-site may still develop.
     fn arg_to_ref<'r>(arg: &'r Self::Arg<'_>) -> &'r Self;
+
+    /// Clones an argument into an owned value.
+    ///
+    /// Useful in generic contexts where you need to extract a value of an argument, independently of how it is passed.
+    #[doc(hidden)] // for now, users are encouraged to use only call-site of impl AsArg; declaration-site may still develop.
+    fn arg_into_owned(arg: Self::Arg<'_>) -> Self;
 }

godot-core/src/obj/dyn_gd.rs

@@ -557,6 +557,10 @@ where
     fn arg_to_ref<'r>(arg: &'r Self::Arg<'_>) -> &'r Self {
         arg.cow_as_ref()
     }
+
+    fn arg_into_owned(arg: Self::Arg<'_>) -> Self {
+        arg.cow_into_owned()
+    }
 }
 
 impl<T, D> meta::ArrayElement for DynGd<T, D>

godot-core/src/obj/gd.rs

@@ -862,6 +862,10 @@ impl<T: GodotClass> ParamType for Gd<T> {
     fn arg_to_ref<'r>(arg: &'r Self::Arg<'_>) -> &'r Self {
         arg.cow_as_ref()
     }
+
+    fn arg_into_owned(arg: Self::Arg<'_>) -> Self {
+        arg.cow_into_owned()
+    }
 }
 
 impl<T: GodotClass> AsArg<Option<Gd<T>>> for Option<&Gd<T>> {
@@ -884,6 +888,10 @@ impl<T: GodotClass> ParamType for Option<Gd<T>> {
     fn arg_to_ref<'r>(arg: &'r Self::Arg<'_>) -> &'r Self {
         arg.cow_as_ref()
     }
+
+    fn arg_into_owned(arg: Self::Arg<'_>) -> Self {
+        arg.cow_into_owned()
+    }
 }
 
 impl<T> Default for Gd<T>