From 365aaa8011c6a0603506d20dcc30117555f6a981 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20K=C3=A5re=20Alsaker?= <john.kare.alsaker@gmail.com>
Date: Tue, 7 Nov 2023 20:06:39 +0100
Subject: [PATCH] Explicitly implement `DynSync` and `DynSend` for `TyCtxt`

---
 compiler/rustc_middle/src/ty/context.rs | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 4a01a24fd6135..36eb70df7d164 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -39,7 +39,9 @@ use rustc_data_structures::profiling::SelfProfilerRef;
 use rustc_data_structures::sharded::{IntoPointer, ShardedHashMap};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::steal::Steal;
-use rustc_data_structures::sync::{FreezeReadGuard, Lock, WorkerLocal};
+use rustc_data_structures::sync::{self, FreezeReadGuard, Lock, WorkerLocal};
+#[cfg(parallel_compiler)]
+use rustc_data_structures::sync::{DynSend, DynSync};
 use rustc_data_structures::unord::UnordSet;
 use rustc_errors::{
     DecorateLint, DiagnosticBuilder, DiagnosticMessage, ErrorGuaranteed, MultiSpan,
@@ -552,6 +554,16 @@ pub struct TyCtxt<'tcx> {
     gcx: &'tcx GlobalCtxt<'tcx>,
 }
 
+// Explicitly implement `DynSync` and `DynSend` for `TyCtxt` to short circuit trait resolution.
+#[cfg(parallel_compiler)]
+unsafe impl DynSend for TyCtxt<'_> {}
+#[cfg(parallel_compiler)]
+unsafe impl DynSync for TyCtxt<'_> {}
+fn _assert_tcx_fields() {
+    sync::assert_dyn_sync::<&'_ GlobalCtxt<'_>>();
+    sync::assert_dyn_send::<&'_ GlobalCtxt<'_>>();
+}
+
 impl<'tcx> Deref for TyCtxt<'tcx> {
     type Target = &'tcx GlobalCtxt<'tcx>;
     #[inline(always)]