fix compile error for multiple async method arguments (#4035)

newsfragments/4035.fixed.md

@@ -0,0 +1 @@
+Fix compile error for `async fn` in `#[pymethods]` with a `&self` receiver and more than one additional argument.

pyo3-macros-backend/src/method.rs

@@ -522,33 +522,22 @@ impl<'a> FnSpec<'a> {
                     Some(cls) => quote!(Some(<#cls as #pyo3_path::PyTypeInfo>::NAME)),
                     None => quote!(None),
                 };
-                let evaluate_args = || -> (Vec<Ident>, TokenStream) {
-                    let mut arg_names = Vec::with_capacity(args.len());
-                    let mut evaluate_arg = quote! {};
-                    for arg in &args {
-                        let arg_name = format_ident!("arg_{}", arg_names.len());
-                        arg_names.push(arg_name.clone());
-                        evaluate_arg.extend(quote! {
-                            let #arg_name = #arg
-                        });
-                    }
-                    (arg_names, evaluate_arg)
-                };
+                let arg_names = (0..args.len())
+                    .map(|i| format_ident!("arg_{}", i))
+                    .collect::<Vec<_>>();
                 let future = match self.tp {
                     FnType::Fn(SelfType::Receiver { mutable: false, .. }) => {
-                        let (arg_name, evaluate_arg) = evaluate_args();
                         quote! {{
-                            #evaluate_arg;
+                            #(let #arg_names = #args;)*
                             let __guard = #pyo3_path::impl_::coroutine::RefGuard::<#cls>::new(&#pyo3_path::impl_::pymethods::BoundRef::ref_from_ptr(py, &_slf))?;
-                            async move { function(&__guard, #(#arg_name),*).await }
+                            async move { function(&__guard, #(#arg_names),*).await }
                         }}
                     }
                     FnType::Fn(SelfType::Receiver { mutable: true, .. }) => {
-                        let (arg_name, evaluate_arg) = evaluate_args();
                         quote! {{
-                            #evaluate_arg;
+                            #(let #arg_names = #args;)*
                             let mut __guard = #pyo3_path::impl_::coroutine::RefMutGuard::<#cls>::new(&#pyo3_path::impl_::pymethods::BoundRef::ref_from_ptr(py, &_slf))?;
-                            async move { function(&mut __guard, #(#arg_name),*).await }
+                            async move { function(&mut __guard, #(#arg_names),*).await }
                         }}
                     }
                     _ => {

tests/test_coroutine.rs

@@ -245,39 +245,6 @@ fn coroutine_panic() {
     })
 }
 
-#[test]
-fn test_async_method_receiver_with_other_args() {
-    #[pyclass]
-    struct Value(i32);
-    #[pymethods]
-    impl Value {
-        #[new]
-        fn new() -> Self {
-            Self(0)
-        }
-        async fn get_value_plus_with(&self, v: i32) -> i32 {
-            self.0 + v
-        }
-        async fn set_value(&mut self, new_value: i32) -> i32 {
-            self.0 = new_value;
-            self.0
-        }
-    }
-
-    Python::with_gil(|gil| {
-        let test = r#"
-        import asyncio
-
-        v = Value()
-        assert asyncio.run(v.get_value_plus_with(3)) == 3
-        assert asyncio.run(v.set_value(10)) == 10
-        assert asyncio.run(v.get_value_plus_with(1)) == 11
-        "#;
-        let locals = [("Value", gil.get_type_bound::<Value>())].into_py_dict_bound(gil);
-        py_run!(gil, *locals, test);
-    });
-}
-
 #[test]
 fn test_async_method_receiver() {
     #[pyclass]
@@ -341,3 +308,36 @@ fn test_async_method_receiver() {
 
     assert!(IS_DROPPED.load(Ordering::SeqCst));
 }
+
+#[test]
+fn test_async_method_receiver_with_other_args() {
+    #[pyclass]
+    struct Value(i32);
+    #[pymethods]
+    impl Value {
+        #[new]
+        fn new() -> Self {
+            Self(0)
+        }
+        async fn get_value_plus_with(&self, v1: i32, v2: i32) -> i32 {
+            self.0 + v1 + v2
+        }
+        async fn set_value(&mut self, new_value: i32) -> i32 {
+            self.0 = new_value;
+            self.0
+        }
+    }
+
+    Python::with_gil(|gil| {
+        let test = r#"
+        import asyncio
+
+        v = Value()
+        assert asyncio.run(v.get_value_plus_with(3, 0)) == 3
+        assert asyncio.run(v.set_value(10)) == 10
+        assert asyncio.run(v.get_value_plus_with(1, 1)) == 12
+        "#;
+        let locals = [("Value", gil.get_type_bound::<Value>())].into_py_dict_bound(gil);
+        py_run!(gil, *locals, test);
+    });
+}