RUST-439 Return errors when unacknowledged write concerns are passed in (#184)

Author: isabelatkinson

src/client/executor.rs

@@ -38,6 +38,13 @@ impl Client {
     /// an implicit session will be created if the operation and write concern are compatible with
     /// sessions.
     pub(crate) async fn execute_operation<T: Operation>(&self, op: T) -> Result<T::O> {
+        // TODO RUST-9: allow unacknowledged write concerns
+        if !op.is_acknowledged() {
+            return Err(ErrorKind::ArgumentError {
+                message: "Unacknowledged write concerns are not supported".to_string(),
+            }
+            .into());
+        }
         let mut implicit_session = self.start_implicit_session(&op).await?;
         self.select_server_and_execute_operation(op, implicit_session.as_mut())
             .await

src/concern/test.rs

@@ -122,3 +122,25 @@ async fn inconsistent_write_concern_rejected() {
         .expect_err("insert should fail");
     assert!(matches!(error.kind.as_ref(), ErrorKind::ArgumentError { .. }));
 }
+
+#[cfg_attr(feature = "tokio-runtime", tokio::test)]
+#[cfg_attr(feature = "async-std-runtime", async_std::test)]
+#[function_name::named]
+async fn unacknowledged_write_concern_rejected() {
+    let _guard = LOCK.run_concurrently().await;
+
+    let client = TestClient::new().await;
+    let db = client.database(function_name!());
+    let error = db
+        .run_command(
+            doc! {
+                "insert": function_name!(),
+                "documents": [ {} ],
+                "writeConcern": { "w": 0 }
+            },
+            None,
+        )
+        .await
+        .expect_err("insert should fail");
+    assert!(matches!(error.kind.as_ref(), ErrorKind::ArgumentError { .. }));
+}