add regression test for Map::fetch() being Unpin

tests/postgres-macros.rs

@@ -1,6 +1,8 @@
 use sqlx::Postgres;
 use sqlx_test::new;
 
+use futures::TryStreamExt;
+
 #[cfg_attr(feature = "runtime-async-std", async_std::test)]
 #[cfg_attr(feature = "runtime-tokio", tokio::test)]
 async fn test_query() -> anyhow::Result<()> {
@@ -244,3 +246,21 @@ async fn test_array_from_slice() -> anyhow::Result<()> {
 
     Ok(())
 }
+
+#[cfg_attr(feature = "runtime-async-std", async_std::test)]
+#[cfg_attr(feature = "runtime-tokio", tokio::test)]
+async fn fetch_is_usable_issue_224() -> anyhow::Result<()> {
+    // ensures that the stream returned by `query::Map::fetch()` is usable with `TryStreamExt`
+    let mut conn = new::<Postgres>().await?;
+
+    let mut stream =
+        sqlx::query!("select * from generate_series(1, 3) as series(num);").fetch(&mut conn);
+
+    // `num` is generated by a function so we can't assume it's non-null
+    assert_eq!(stream.try_next().await?.unwrap().num, Some(1));
+    assert_eq!(stream.try_next().await?.unwrap().num, Some(2));
+    assert_eq!(stream.try_next().await?.unwrap().num, Some(3));
+    assert!(stream.try_next().await?.is_none());
+
+    Ok(())
+}