From a1850f83c458fb8966cf44f5d96ed8f0f9328643 Mon Sep 17 00:00:00 2001
From: David Pedersen <david.pdrsn@gmail.com>
Date: Wed, 12 May 2021 09:58:21 +0200
Subject: [PATCH] feat(metadata): remove manual `Send + Sync` impls for
 metadata types

Removes manual `Send` and `Sync` impls for these types as they weren't
necessary:

- `metadata::Iter`
- `metadata::IterMut`
- `metadata::ValueDrain`
- `metadata::ValueIterMut`

Since all the types they contained were `Send + Sync` we can rely on the
compiler automatically adding the impls.

Also added some tests to ensure we don't accidentally make them `!Send`
or `!Sync` in the future.

Fixes https://github.com/hyperium/tonic/issues/636
---
 tonic/src/metadata/map.rs | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/tonic/src/metadata/map.rs b/tonic/src/metadata/map.rs
index cbef3e101..461a9fb54 100644
--- a/tonic/src/metadata/map.rs
+++ b/tonic/src/metadata/map.rs
@@ -1244,9 +1244,6 @@ impl<'a> Iterator for Iter<'a> {
     }
 }
 
-unsafe impl<'a> Sync for Iter<'a> {}
-unsafe impl<'a> Send for Iter<'a> {}
-
 // ===== impl IterMut =====
 
 impl<'a> Iterator for IterMut<'a> {
@@ -1274,9 +1271,6 @@ impl<'a> Iterator for IterMut<'a> {
     }
 }
 
-unsafe impl<'a> Sync for IterMut<'a> {}
-unsafe impl<'a> Send for IterMut<'a> {}
-
 // ===== impl ValueDrain =====
 
 impl<'a, VE: ValueEncoding> Iterator for ValueDrain<'a, VE> {
@@ -1293,9 +1287,6 @@ impl<'a, VE: ValueEncoding> Iterator for ValueDrain<'a, VE> {
     }
 }
 
-unsafe impl<'a, VE: ValueEncoding> Sync for ValueDrain<'a, VE> {}
-unsafe impl<'a, VE: ValueEncoding> Send for ValueDrain<'a, VE> {}
-
 // ===== impl Keys =====
 
 impl<'a> Iterator for Keys<'a> {
@@ -1425,9 +1416,6 @@ where
     }
 }
 
-unsafe impl<'a, VE: ValueEncoding> Sync for ValueIterMut<'a, VE> {}
-unsafe impl<'a, VE: ValueEncoding> Send for ValueIterMut<'a, VE> {}
-
 // ===== impl Entry =====
 
 impl<'a, VE: ValueEncoding> Entry<'a, VE> {
@@ -2725,4 +2713,18 @@ mod tests {
         }
         assert!(found_x_word_bin);
     }
+
+    #[allow(dead_code)]
+    fn value_drain_is_send_sync() {
+        fn is_send_sync<T: Send + Sync>() {}
+
+        is_send_sync::<Iter<'_>>();
+        is_send_sync::<IterMut<'_>>();
+
+        is_send_sync::<ValueDrain<'_, Ascii>>();
+        is_send_sync::<ValueDrain<'_, Binary>>();
+
+        is_send_sync::<ValueIterMut<'_, Ascii>>();
+        is_send_sync::<ValueIterMut<'_, Binary>>();
+    }
 }