Match specifically Arc<Self>, not any other Arc

Author: dtolnay

src/expand.rs

@@ -9,9 +9,9 @@ use std::mem;
 use syn::punctuated::Punctuated;
 use syn::visit_mut::{self, VisitMut};
 use syn::{
-    parse_quote, parse_quote_spanned, Attribute, Block, FnArg, GenericParam, Generics, Ident,
-    ImplItem, Lifetime, LifetimeDef, Pat, PatIdent, Receiver, ReturnType, Signature, Stmt, Token,
-    TraitItem, Type, TypePath, WhereClause,
+    parse_quote, parse_quote_spanned, Attribute, Block, FnArg, GenericArgument, GenericParam,
+    Generics, Ident, ImplItem, Lifetime, LifetimeDef, Pat, PatIdent, PathArguments, Receiver,
+    ReturnType, Signature, Stmt, Token, TraitItem, Type, TypePath, WhereClause,
 };
 
 impl ToTokens for Item {
@@ -242,8 +242,27 @@ fn transform_sig(
                 } =>
             {
                 match arg.ty.as_ref() {
+                    // self: &Self
                     Type::Reference(ty) if ty.mutability.is_none() => &[InferredBound::Sync],
-                    Type::Path(ty) if ty.path.segments.last().unwrap().ident == "Arc" => {
+                    // self: Arc<Self>
+                    Type::Path(ty)
+                        if {
+                            let segment = ty.path.segments.last().unwrap();
+                            segment.ident == "Arc"
+                                && match &segment.arguments {
+                                    PathArguments::AngleBracketed(arguments) => {
+                                        arguments.args.len() == 1
+                                            && match &arguments.args[0] {
+                                                GenericArgument::Type(Type::Path(arg)) => {
+                                                    arg.path.is_ident("Self")
+                                                }
+                                                _ => false,
+                                            }
+                                    }
+                                    _ => false,
+                                }
+                        } =>
+                    {
                         &[InferredBound::Sync, InferredBound::Send]
                     }
                     _ => &[InferredBound::Send],