Add helper to return result from a future

Author: swsnr

gio/src/dbus_method_invocation.rs

@@ -45,4 +45,25 @@ impl DBusMethodInvocation {
             Err(error) => self.return_gerror(error),
         }
     }
+
+    // rustdoc-stripper-ignore-next
+    /// Return an async result for this invocation.
+    ///
+    /// Spawn the given future on the thread-default main context, and return the
+    /// the result with [`return_result`].  Specifically, if a variant is returned
+    /// that is not a tuple it is automatically wrapped into a tuple.
+    ///
+    /// The given `Future` does not have to be `Send`.
+    ///
+    /// This can be called only from the thread where the main context is running, e.g.
+    /// from any other `Future` that is executed on this main context, or after calling
+    /// `with_thread_default` or `acquire` on the main context.
+    pub fn return_future_local<F>(self, f: F) -> glib::JoinHandle<()>
+    where
+        F: std::future::Future<Output = Result<Option<glib::Variant>, glib::Error>> + 'static,
+    {
+        glib::spawn_future_local(async move {
+            self.return_result(f.await);
+        })
+    }
 }