Add Python annotations for the return type for async functions (#1984)

Author: giarc3

fixtures/futures/src/lib.rs

@@ -101,6 +101,12 @@ pub async fn sleep(ms: u16) -> bool {
     true
 }
 
+/// Async function that sleeps with no return type
+#[uniffi::export]
+pub async fn sleep_no_return(ms: u16) {
+    TimerFuture::new(Duration::from_millis(ms.into())).await;
+}
+
 // Our error.
 #[derive(thiserror::Error, uniffi::Error, Debug)]
 pub enum MyError {

fixtures/futures/tests/bindings/test_futures.py

@@ -208,5 +208,11 @@ async def test():
             await use_shared_resource(SharedResourceOptions(release_after_ms=0, timeout_ms=1000))
         asyncio.run(test())
 
+    def test_function_annotations(self):
+        async def test():
+            assert sleep.__annotations__ == {"ms": "int", "return": "bool"}
+            assert sleep_no_return.__annotations__ == {"ms": "int", "return": None}
+        asyncio.run(test())
+
 if __name__ == '__main__':
     unittest.main()

uniffi_bindgen/src/bindings/python/templates/TopLevelFunctionTemplate.py

@@ -1,9 +1,15 @@
 {%- if func.is_async() %}
 
-def {{ func.name()|fn_name }}({%- call py::arg_list_decl(func) -%}):
+{%- match func.return_type() -%}
+{%- when Some with (return_type) %}
+async def {{ func.name()|fn_name }}({%- call py::arg_list_decl(func) -%}) -> "{{ return_type|type_name }}":
+{% when None %}
+async def {{ func.name()|fn_name }}({%- call py::arg_list_decl(func) -%}) -> None:
+{% endmatch %}
+
     {%- call py::docstring(func, 4) %}
     {%- call py::setup_args(func) %}
-    return _uniffi_rust_call_async(
+    return await _uniffi_rust_call_async(
         _UniffiLib.{{ func.ffi_func().name() }}({% call py::arg_list_lowered(func) %}),
         _UniffiLib.{{func.ffi_rust_future_poll(ci) }},
         _UniffiLib.{{func.ffi_rust_future_complete(ci) }},
@@ -34,7 +40,7 @@ def {{ func.name()|fn_name }}({%- call py::arg_list_decl(func) -%}) -> "{{ retur
     return {{ return_type|lift_fn }}({% call py::to_ffi_call(func) %})
 {% when None %}
 
-def {{ func.name()|fn_name }}({%- call py::arg_list_decl(func) -%}):
+def {{ func.name()|fn_name }}({%- call py::arg_list_decl(func) -%}) -> None:
     {%- call py::docstring(func, 4) %}
     {%- call py::setup_args(func) %}
     {% call py::to_ffi_call(func) %}

uniffi_bindgen/src/bindings/python/templates/macros.py

@@ -115,10 +115,16 @@
 {%- macro method_decl(py_method_name, meth) %}
 {%  if meth.is_async() %}
 
-    def {{ py_method_name }}(self, {% call arg_list_decl(meth) %}):
+{%-     match meth.return_type() %}
+{%-         when Some with (return_type) %}
+    async def {{ py_method_name }}(self, {% call arg_list_decl(meth) %}) -> "{{ return_type|type_name }}":
+{%-         when None %}
+    async def {{ py_method_name }}(self, {% call arg_list_decl(meth) %}) -> None:
+{%      endmatch %}
+
         {%- call docstring(meth, 8) %}
         {%- call setup_args_extra_indent(meth) %}
-        return _uniffi_rust_call_async(
+        return await _uniffi_rust_call_async(
             _UniffiLib.{{ meth.ffi_func().name() }}(
                 self._uniffi_clone_pointer(), {% call arg_list_lowered(meth) %}
             ),
@@ -155,7 +161,7 @@ def {{ py_method_name }}(self, {% call arg_list_decl(meth) %}) -> "{{ return_typ
 
 {%-         when None %}
 
-    def {{ py_method_name }}(self, {% call arg_list_decl(meth) %}):
+    def {{ py_method_name }}(self, {% call arg_list_decl(meth) %}) -> None:
         {%- call docstring(meth, 8) %}
         {%- call setup_args_extra_indent(meth) %}
         {% call to_ffi_call_with_prefix("self._uniffi_clone_pointer()", meth) %}