Change XCM builder methods to take and return mutable references

Author: franciscoaguirre

polkadot/xcm/procedural/src/builder_pattern.rs

@@ -92,7 +92,7 @@ fn generate_builder_raw_impl(name: &Ident, data_enum: &DataEnum) -> TokenStream2
 		let method = match &variant.fields {
 			Fields::Unit => {
 				quote! {
-					pub fn #method_name(mut self) -> Self {
+					pub fn #method_name(&mut self) -> &mut Self {
 						self.instructions.push(#name::<Call>::#variant_name);
 						self
 					}
@@ -107,7 +107,7 @@ fn generate_builder_raw_impl(name: &Ident, data_enum: &DataEnum) -> TokenStream2
 					.collect();
 				let arg_types: Vec<_> = fields.unnamed.iter().map(|field| &field.ty).collect();
 				quote! {
-					pub fn #method_name(mut self, #(#arg_names: #arg_types),*) -> Self {
+					pub fn #method_name(&mut self, #(#arg_names: #arg_types),*) -> &mut Self {
 						self.instructions.push(#name::<Call>::#variant_name(#(#arg_names),*));
 						self
 					}
@@ -117,7 +117,7 @@ fn generate_builder_raw_impl(name: &Ident, data_enum: &DataEnum) -> TokenStream2
 				let arg_names: Vec<_> = fields.named.iter().map(|field| &field.ident).collect();
 				let arg_types: Vec<_> = fields.named.iter().map(|field| &field.ty).collect();
 				quote! {
-					pub fn #method_name(mut self, #(#arg_names: #arg_types),*) -> Self {
+					pub fn #method_name(&mut self, #(#arg_names: #arg_types),*) -> &mut Self {
 						self.instructions.push(#name::<Call>::#variant_name { #(#arg_names),* });
 						self
 					}