Explicitly move all arguments into the async block

Author: mendess

trait-variant/Cargo.toml

@@ -25,7 +25,7 @@ proc-macro = true
 [dependencies]
 proc-macro2 = "1.0"
 quote = "1.0"
-syn = { version = "2.0", features = ["full"] }
+syn = { version = "2.0", features = ["full", "visit-mut"] }
 
 [dev-dependencies]
 tokio = { version = "1", features = ["rt"] }

trait-variant/examples/variant.rs

@@ -21,8 +21,8 @@ pub trait LocalIntFactory {
     fn stream(&self) -> impl Iterator<Item = i32>;
     fn call(&self) -> u32;
     fn another_async(&self, input: Result<(), &str>) -> Self::MyFut<'_>;
-    async fn defaulted(&self) -> i32 {
-        self.make(10, "10").await
+    async fn defaulted(&self, x: u32) -> i32 {
+        self.make(x, "10").await
     }
     async fn defaulted_mut(&mut self) -> i32 {
         self.make(10, "10").await

trait-variant/src/variant.rs

@@ -15,9 +15,9 @@ use syn::{
     parse_macro_input, parse_quote,
     punctuated::Punctuated,
     token::{Comma, Plus},
-    Error, FnArg, GenericParam, Generics, Ident, ItemTrait, Lifetime, Pat, PatType, Receiver,
-    Result, ReturnType, Signature, Token, TraitBound, TraitItem, TraitItemConst, TraitItemFn,
-    TraitItemType, Type, TypeImplTrait, TypeParamBound, TypeReference, WhereClause,
+    Error, FnArg, GenericParam, Generics, Ident, ItemTrait, Lifetime, Pat, PatIdent, PatType,
+    Receiver, Result, ReturnType, Signature, Token, TraitBound, TraitItem, TraitItemConst,
+    TraitItemFn, TraitItemType, Type, TypeImplTrait, TypeParamBound, TypeReference, WhereClause,
 };
 
 struct Attrs {
@@ -145,10 +145,32 @@ fn transform_item(item: &TraitItem, bounds: &Vec<TypeParamBound>) -> TraitItem {
                 output: ReturnType::Type(syn::parse2(quote! { -> }).unwrap(), Box::new(ty)),
                 ..sig.clone()
             },
-            fn_item
-                .default
-                .as_ref()
-                .map(|b| syn::parse2(quote! { { async move #b } }).unwrap()),
+            fn_item.default.as_ref().map(|b| {
+                let items = sig.inputs.iter().map(|i| match i {
+                    FnArg::Receiver(Receiver { self_token, .. }) => {
+                        quote! { let __self = #self_token; }
+                    }
+                    FnArg::Typed(PatType { pat, .. }) => match pat.as_ref() {
+                        Pat::Ident(PatIdent { ident, .. }) => quote! { let #ident = #ident; },
+                        _ => todo!(),
+                    },
+                });
+
+                struct ReplaceSelfVisitor;
+                impl syn::visit_mut::VisitMut for ReplaceSelfVisitor {
+                    fn visit_ident_mut(&mut self, ident: &mut syn::Ident) {
+                        if ident == "self" {
+                            *ident = syn::Ident::new("__self", ident.span());
+                        }
+                        syn::visit_mut::visit_ident_mut(self, ident);
+                    }
+                }
+
+                let mut block = b.clone();
+                syn::visit_mut::visit_block_mut(&mut ReplaceSelfVisitor, &mut block);
+
+                parse_quote! { { async move { #(#items)* #block} } }
+            }),
         )
     } else {
         match &sig.output {