Handle async impl fn without body

Author: dtolnay

Cargo.toml

@@ -17,7 +17,7 @@ proc-macro = true
 [dependencies]
 proc-macro2 = "1.0"
 quote = "1.0"
-syn = { version = "2.0", features = ["full", "visit-mut"] }
+syn = { version = "2.0.9", features = ["full", "visit-mut"] }
 
 [dev-dependencies]
 futures = "0.3"

src/expand.rs

@@ -2,6 +2,7 @@ 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};
+use crate::verbatim::VerbatimFn;
 use proc_macro2::{Span, TokenStream};
 use quote::{format_ident, quote, quote_spanned, ToTokens};
 use std::collections::BTreeSet as Set;
@@ -11,7 +12,7 @@ use syn::visit_mut::{self, VisitMut};
 use syn::{
     parse_quote, parse_quote_spanned, Attribute, Block, FnArg, GenericArgument, GenericParam,
     Generics, Ident, ImplItem, Lifetime, LifetimeParam, Pat, PatIdent, PathArguments, Receiver,
-    ReturnType, Signature, Stmt, Token, TraitItem, Type, TypePath, WhereClause,
+    ReturnType, Signature, Token, TraitItem, Type, TypePath, WhereClause,
 };
 
 impl ToTokens for Item {
@@ -94,15 +95,27 @@ pub fn expand(input: &mut Item, is_local: bool) {
                 associated_type_impl_traits: &associated_type_impl_traits,
             };
             for inner in &mut input.items {
-                if let ImplItem::Fn(method) = inner {
-                    let sig = &mut method.sig;
-                    if sig.asyncness.is_some() {
+                match inner {
+                    ImplItem::Fn(method) if method.sig.asyncness.is_some() => {
+                        let sig = &mut method.sig;
                         let block = &mut method.block;
                         let has_self = has_self_in_sig(sig) || has_self_in_block(block);
                         transform_block(context, sig, block);
                         transform_sig(context, sig, has_self, false, is_local);
                         method.attrs.push(lint_suppress_with_body());
                     }
+                    ImplItem::Verbatim(tokens) => {
+                        let mut method = match syn::parse2::<VerbatimFn>(tokens.clone()) {
+                            Ok(method) if method.sig.asyncness.is_some() => method,
+                            _ => continue,
+                        };
+                        let sig = &mut method.sig;
+                        let has_self = has_self_in_sig(sig);
+                        transform_sig(context, sig, has_self, false, is_local);
+                        method.attrs.push(lint_suppress_with_body());
+                        *tokens = quote!(#method);
+                    }
+                    _ => {}
                 }
             }
         }
@@ -329,12 +342,6 @@ fn transform_sig(
 //         ___ret
 //     })
 fn transform_block(context: Context, sig: &mut Signature, block: &mut Block) {
-    if let Some(Stmt::Item(syn::Item::Verbatim(item))) = block.stmts.first() {
-        if block.stmts.len() == 1 && item.to_string() == ";" {
-            return;
-        }
-    }
-
     let mut self_span = None;
     let decls = sig
         .inputs

src/lib.rs

@@ -325,6 +325,7 @@ mod expand;
 mod lifetime;
 mod parse;
 mod receiver;
+mod verbatim;
 
 use crate::args::Args;
 use crate::expand::expand;

src/verbatim.rs

@@ -0,0 +1,34 @@
+use proc_macro2::TokenStream;
+use quote::{ToTokens, TokenStreamExt};
+use syn::parse::{Parse, ParseStream, Result};
+use syn::{Attribute, Signature, Token, Visibility};
+
+pub struct VerbatimFn {
+    pub attrs: Vec<Attribute>,
+    pub vis: Visibility,
+    pub defaultness: Option<Token![default]>,
+    pub sig: Signature,
+    pub semi_token: Token![;],
+}
+
+impl Parse for VerbatimFn {
+    fn parse(input: ParseStream) -> Result<Self> {
+        Ok(VerbatimFn {
+            attrs: input.call(Attribute::parse_outer)?,
+            vis: input.parse()?,
+            defaultness: input.parse()?,
+            sig: input.parse()?,
+            semi_token: input.parse()?,
+        })
+    }
+}
+
+impl ToTokens for VerbatimFn {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        tokens.append_all(&self.attrs);
+        self.vis.to_tokens(tokens);
+        self.defaultness.to_tokens(tokens);
+        self.sig.to_tokens(tokens);
+        self.semi_token.to_tokens(tokens);
+    }
+}