Split context lifetimes from sig params loop

Author: dtolnay

src/expand.rs

@@ -8,8 +8,8 @@ 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, Pat, PatIdent, Receiver, ReturnType, Signature, Stmt, Token, TraitItem,
-    Type, TypeParamBound, TypePath, WhereClause,
+    ImplItem, Lifetime, LifetimeDef, Pat, PatIdent, Receiver, ReturnType, Signature, Stmt, Token,
+    TraitItem, Type, TypeParamBound, TypePath, WhereClause,
 };
 
 impl ToTokens for Item {
@@ -34,17 +34,18 @@ enum Context<'a> {
 }
 
 impl Context<'_> {
-    fn lifetimes<'a>(&'a self, used: &'a [Lifetime]) -> impl Iterator<Item = &'a GenericParam> {
+    fn lifetimes<'a>(&'a self, used: &'a [Lifetime]) -> impl Iterator<Item = &'a LifetimeDef> {
         let generics = match self {
             Context::Trait { generics, .. } => generics,
             Context::Impl { impl_generics, .. } => impl_generics,
         };
-        generics.params.iter().filter(move |param| {
+        generics.params.iter().filter_map(move |param| {
             if let GenericParam::Lifetime(param) = param {
-                used.contains(&param.lifetime)
-            } else {
-                false
+                if used.contains(&param.lifetime) {
+                    return Some(param);
+                }
             }
+            None
         })
     }
 }
@@ -178,12 +179,7 @@ fn transform_sig(
         }
     }
 
-    for param in sig
-        .generics
-        .params
-        .iter()
-        .chain(context.lifetimes(&lifetimes.explicit))
-    {
+    for param in &sig.generics.params {
         match param {
             GenericParam::Type(param) => {
                 let param = &param.ident;
@@ -203,6 +199,14 @@ fn transform_sig(
         }
     }
 
+    for param in context.lifetimes(&lifetimes.explicit) {
+        let param = &param.lifetime;
+        let span = param.span();
+        where_clause_or_default(&mut sig.generics.where_clause)
+            .predicates
+            .push(parse_quote_spanned!(span=> #param: 'async_trait));
+    }
+
     if sig.generics.lt_token.is_none() {
         sig.generics.lt_token = Some(Token![<](sig.ident.span()));
     }