From 64bcf13563c5c18825692c63035cb1843a577b28 Mon Sep 17 00:00:00 2001
From: Ruben De Smet <ruben.de.smet@rubdos.be>
Date: Thu, 2 Jan 2025 16:46:41 +0100
Subject: [PATCH] fix: Ensure Send+Sync bounds on SentryLayer and SentryService

Updates PhantomData usage in SentryLayer and SentryService to explicitly
ensure Send+Sync trait bounds using the fn pointer pattern as documented in
the Rust Nomicon.
---
 sentry-tower/src/lib.rs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/sentry-tower/src/lib.rs b/sentry-tower/src/lib.rs
index 4cd9818da..71fb05e84 100644
--- a/sentry-tower/src/lib.rs
+++ b/sentry-tower/src/lib.rs
@@ -196,7 +196,9 @@ where
     H: Into<Arc<Hub>>,
 {
     provider: P,
-    _hub: PhantomData<(H, Request)>,
+    // `fn` is used to assert that SentryLayer will be Send+Sync
+    // (https://doc.rust-lang.org/nomicon/phantom-data.html#table-of-phantomdata-patterns)
+    _hub: PhantomData<fn(H, Request)>,
 }
 
 impl<S, P, H, Request> Layer<S> for SentryLayer<P, H, Request>
@@ -250,7 +252,9 @@ where
 {
     service: S,
     provider: P,
-    _hub: PhantomData<(H, Request)>,
+    // `fn` is used to assert that SentryService will be Send+Sync
+    // (https://doc.rust-lang.org/nomicon/phantom-data.html#table-of-phantomdata-patterns)
+    _hub: PhantomData<fn(H, Request)>,
 }
 
 impl<S, Request, P, H> Service<Request> for SentryService<S, P, H, Request>