Rust: Make api method future implement Send/Sync

The `Request::execute` method captures a
`url::form_urlencoded::Serializer` in the generator,
which causes the overall future to be !Send/!Sync

To avoid capturing this, I've explicitly introduced a new
scope (just using `drop` doesn't work). I've also added a test
to make sure that this doesn't regress.

Author: svix-aaron1011

rust/src/api.rs

@@ -1284,3 +1284,18 @@ impl<'a> Statistics<'a> {
         statistics_api::v1_statistics_aggregate_event_types(self.cfg).await
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::api::Svix;
+
+    #[test]
+    fn test_future_send_sync() {
+        fn require_send_sync<T: Send + Sync>(_: T) {}
+
+        let svix = Svix::new(String::new(), None);
+        let message_api = svix.message();
+        let fut = message_api.expunge_content(String::new(), String::new());
+        require_send_sync(fut);
+    }
+}

rust/src/request.rs

@@ -85,24 +85,28 @@ impl Request {
     }
 
     pub async fn execute<T: DeserializeOwned>(self, conf: &Configuration) -> Result<T, Error> {
-        let mut query_string = ::url::form_urlencoded::Serializer::new("".to_owned());
-
         let mut path = self.path;
         for (k, v) in self.path_params {
             // replace {id} with the value of the id path param
             path = path.replace(&format!("{{{k}}}"), &v);
         }
 
-        for (key, val) in self.query_params {
-            query_string.append_pair(&key, &val);
-        }
-
         let mut uri = format!("{}{}", conf.base_path, path);
 
-        let query_string_str = query_string.finish();
-        if !query_string_str.is_empty() {
-            uri += "?";
-            uri += &query_string_str;
+        // Work around rustc issue - we need to make sure that `query_string` is not captured
+        // by the outer `async` generator. Using `drop(query_string)` is insufficient, so we
+        // create a new scope
+        {
+            let mut query_string = ::url::form_urlencoded::Serializer::new("".to_owned());
+            for (key, val) in self.query_params {
+                query_string.append_pair(&key, &val);
+            }
+
+            let query_string_str = query_string.finish();
+            if !query_string_str.is_empty() {
+                uri += "?";
+                uri += &query_string_str;
+            }
         }
 
         let mut req_builder = http1::Request::builder().uri(uri).method(self.method);