From ca9f7ee9f4750d6bb8a073ab4df1b7e4555857ad Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20Heine=20n=C3=A9=20Lang?= <mail@adrianheine.de>
Date: Sat, 25 Feb 2023 18:06:17 +0100
Subject: [PATCH] macros: fix empty `join!` and `try_join!` (#5504)

Fixes: #5502
---
 tokio/src/macros/join.rs       | 4 +++-
 tokio/src/macros/try_join.rs   | 4 +++-
 tokio/tests/macros_join.rs     | 6 ++++++
 tokio/tests/macros_try_join.rs | 5 +++++
 4 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/tokio/src/macros/join.rs b/tokio/src/macros/join.rs
index 7e85203c0..8a0198600 100644
--- a/tokio/src/macros/join.rs
+++ b/tokio/src/macros/join.rs
@@ -158,7 +158,9 @@ macro_rules! join {
 
     // ===== Entry point =====
 
-    ( $($e:expr),* $(,)?) => {
+    ( $($e:expr),+ $(,)?) => {
         $crate::join!(@{ () (0) } $($e,)*)
     };
+
+    () => { async {}.await }
 }
diff --git a/tokio/src/macros/try_join.rs b/tokio/src/macros/try_join.rs
index 597cd5df0..7b1237092 100644
--- a/tokio/src/macros/try_join.rs
+++ b/tokio/src/macros/try_join.rs
@@ -210,7 +210,9 @@ macro_rules! try_join {
 
     // ===== Entry point =====
 
-    ( $($e:expr),* $(,)?) => {
+    ( $($e:expr),+ $(,)?) => {
         $crate::try_join!(@{ () (0) } $($e,)*)
     };
+
+    () => { async { Ok(()) }.await }
 }
diff --git a/tokio/tests/macros_join.rs b/tokio/tests/macros_join.rs
index a87c6a6f8..7866ac086 100644
--- a/tokio/tests/macros_join.rs
+++ b/tokio/tests/macros_join.rs
@@ -153,3 +153,9 @@ async fn a_different_future_is_polled_first_every_time_poll_fn_is_polled() {
         *poll_order.lock().unwrap()
     );
 }
+
+#[tokio::test]
+#[allow(clippy::unit_cmp)]
+async fn empty_join() {
+    assert_eq!(tokio::join!(), ());
+}
diff --git a/tokio/tests/macros_try_join.rs b/tokio/tests/macros_try_join.rs
index 6c432221d..74b1c9f94 100644
--- a/tokio/tests/macros_try_join.rs
+++ b/tokio/tests/macros_try_join.rs
@@ -183,3 +183,8 @@ async fn a_different_future_is_polled_first_every_time_poll_fn_is_polled() {
         *poll_order.lock().unwrap()
     );
 }
+
+#[tokio::test]
+async fn empty_try_join() {
+    assert_eq!(tokio::try_join!() as Result<_, ()>, Ok(()));
+}