Create enum for the different possible inferred bounds

src/bound.rs

@@ -0,0 +1,46 @@
+use proc_macro2::{Ident, Span};
+use syn::punctuated::Punctuated;
+use syn::{Token, TypeParamBound};
+
+pub type Supertraits = Punctuated<TypeParamBound, Token![+]>;
+
+pub enum InferredBound {
+    Send,
+    Sync,
+}
+
+pub fn has_bound(supertraits: &Supertraits, bound: &InferredBound) -> bool {
+    for supertrait in supertraits {
+        if let TypeParamBound::Trait(supertrait) = supertrait {
+            if supertrait.path.is_ident(bound)
+                || supertrait.path.segments.len() == 3
+                    && (supertrait.path.segments[0].ident == "std"
+                        || supertrait.path.segments[0].ident == "core")
+                    && supertrait.path.segments[1].ident == "marker"
+                    && supertrait.path.segments[2].ident == *bound
+            {
+                return true;
+            }
+        }
+    }
+    false
+}
+
+impl InferredBound {
+    fn as_str(&self) -> &str {
+        match self {
+            InferredBound::Send => "Send",
+            InferredBound::Sync => "Sync",
+        }
+    }
+
+    pub fn spanned_ident(&self, span: Span) -> Ident {
+        Ident::new(self.as_str(), span)
+    }
+}
+
+impl PartialEq<InferredBound> for Ident {
+    fn eq(&self, bound: &InferredBound) -> bool {
+        self == bound.as_str()
+    }
+}

src/expand.rs

@@ -1,3 +1,4 @@
+use crate::bound::{has_bound, InferredBound, Supertraits};
 use crate::lifetime::{AddLifetimeToImplTrait, CollectLifetimes};
 use crate::parse::Item;
 use crate::receiver::{has_self_in_block, has_self_in_sig, mut_pat, ReplaceSelf};
@@ -10,7 +11,7 @@ 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, TypeParamBound, TypePath, WhereClause,
+    TraitItem, Type, TypePath, WhereClause,
 };
 
 impl ToTokens for Item {
@@ -51,8 +52,6 @@ impl Context<'_> {
     }
 }
 
-type Supertraits = Punctuated<TypeParamBound, Token![+]>;
-
 pub fn expand(input: &mut Item, is_local: bool) {
     match input {
         Item::Trait(input) => {
@@ -235,7 +234,7 @@ fn transform_sig(
                 reference: Some(_),
                 mutability: None,
                 ..
-            })) => Ident::new("Sync", default_span),
+            })) => InferredBound::Sync,
             Some(FnArg::Typed(arg))
                 if match (arg.pat.as_ref(), arg.ty.as_ref()) {
                     (Pat::Ident(pat), Type::Reference(ty)) => {
@@ -244,9 +243,9 @@ fn transform_sig(
                     _ => false,
                 } =>
             {
-                Ident::new("Sync", default_span)
+                InferredBound::Sync
             }
-            _ => Ident::new("Send", default_span),
+            _ => InferredBound::Send,
         };
 
         let assume_bound = match context {
@@ -258,6 +257,7 @@ fn transform_sig(
         where_clause.predicates.push(if assume_bound || is_local {
             parse_quote_spanned!(default_span=> Self: 'async_trait)
         } else {
+            let bound = bound.spanned_ident(default_span);
             parse_quote_spanned!(default_span=> Self: ::core::marker::#bound + 'async_trait)
         });
     }
@@ -402,23 +402,6 @@ fn positional_arg(i: usize, pat: &Pat) -> Ident {
     format_ident!("__arg{}", i, span = span)
 }
 
-fn has_bound(supertraits: &Supertraits, marker: &Ident) -> bool {
-    for bound in supertraits {
-        if let TypeParamBound::Trait(bound) = bound {
-            if bound.path.is_ident(marker)
-                || bound.path.segments.len() == 3
-                    && (bound.path.segments[0].ident == "std"
-                        || bound.path.segments[0].ident == "core")
-                    && bound.path.segments[1].ident == "marker"
-                    && bound.path.segments[2].ident == *marker
-            {
-                return true;
-            }
-        }
-    }
-    false
-}
-
 fn contains_associated_type_impl_trait(context: Context, ret: &mut Type) -> bool {
     struct AssociatedTypeImplTraits<'a> {
         set: &'a Set<Ident>,

src/lib.rs

@@ -318,6 +318,7 @@
 extern crate proc_macro;
 
 mod args;
+mod bound;
 mod expand;
 mod lifetime;
 mod parse;