Merge #924

924: use ManuallyDrop in ptrcalls to prevent drop reordering r=Bromeon a=Waridley

On rustc 1.65.0-nightly (29e4a9ee0 2022-08-10), drops of args in some ptrcalls are seemingly being reordered to before the FFI call. Using `ManuallyDrop` prevents this.

This could potentially be related to #894, but I'm not confident enough to say it will definitely fix it yet.

Co-authored-by: Waridley <[email protected]>

Author: bors[bot]

bindings-generator/src/methods.rs

@@ -468,8 +468,12 @@ mod ptrcall {
                 .map(|(name, ty)| generate_argument_pre(ty, name));
             let return_pre = generate_return_pre(&sig.return_type);
 
+            let arg_forgets = arguments.clone().map(|(name, _)| {
+                quote! { let #name = ::std::mem::ManuallyDrop::new(#name); }
+            });
+
             let arg_drops = arguments.clone().map(|(name, _)| {
-                quote! { drop(#name); }
+                quote! { ::std::mem::ManuallyDrop::into_inner(#name); }
             });
 
             quote! {
@@ -479,6 +483,8 @@ mod ptrcall {
                     #(#args),*
                 ];
 
+                #(#arg_forgets)*
+
                 #return_pre
 
                 (gd_api.godot_method_bind_ptrcall)(method_bind, obj_ptr, argument_buffer.as_mut_ptr() as *mut _, ret_ptr as *mut _);