Do not assert that a change in global cache only happens when concurrent

4 files changed, 11 insertions, 8 deletions

diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 7d3e2c9965d..9a0d2602a5f 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -207,8 +207,9 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
         from_entry(entry)
     }
 
-    fn evaluation_is_concurrent(&self) -> bool {
-        self.sess.threads() > 1
+    fn assert_evaluation_is_concurrent(&self) {
+        // Turns out, the assumption for this function isn't perfect.
+        // See trait-system-refactor-initiative#234.
     }
 
     fn expand_abstract_consts<T: TypeFoldable<TyCtxt<'tcx>>>(self, t: T) -> T {
diff --git a/compiler/rustc_type_ir/src/interner.rs b/compiler/rustc_type_ir/src/interner.rs
index cf58aec14a6..f12dcbfef98 100644
--- a/compiler/rustc_type_ir/src/interner.rs
+++ b/compiler/rustc_type_ir/src/interner.rs
@@ -185,7 +185,9 @@ pub trait Interner:
         from_entry: impl FnOnce(&CanonicalParamEnvCacheEntry<Self>) -> R,
     ) -> R;
 
-    fn evaluation_is_concurrent(&self) -> bool;
+    /// Useful for testing. If a cache entry is replaced, this should
+    /// (in theory) only happen when concurrent.
+    fn assert_evaluation_is_concurrent(&self);
 
     fn expand_abstract_consts<T: TypeFoldable<Self>>(self, t: T) -> T;
 
@@ -569,7 +571,7 @@ impl<I: Interner> search_graph::Cx for I {
     fn with_global_cache<R>(self, f: impl FnOnce(&mut search_graph::GlobalCache<Self>) -> R) -> R {
         I::with_global_cache(self, f)
     }
-    fn evaluation_is_concurrent(&self) -> bool {
-        self.evaluation_is_concurrent()
+    fn assert_evaluation_is_concurrent(&self) {
+        self.assert_evaluation_is_concurrent()
     }
 }
diff --git a/compiler/rustc_type_ir/src/search_graph/global_cache.rs b/compiler/rustc_type_ir/src/search_graph/global_cache.rs
index eb56c1af408..7e438fefffc 100644
--- a/compiler/rustc_type_ir/src/search_graph/global_cache.rs
+++ b/compiler/rustc_type_ir/src/search_graph/global_cache.rs
@@ -56,13 +56,13 @@ impl<X: Cx> GlobalCache<X> {
             let with_overflow = WithOverflow { nested_goals, result };
             let prev = entry.with_overflow.insert(required_depth, with_overflow);
             if let Some(prev) = &prev {
-                assert!(cx.evaluation_is_concurrent());
+                cx.assert_evaluation_is_concurrent();
                 assert_eq!(cx.get_tracked(&prev.result), evaluation_result.result);
             }
         } else {
             let prev = entry.success.replace(Success { required_depth, nested_goals, result });
             if let Some(prev) = &prev {
-                assert!(cx.evaluation_is_concurrent());
+                cx.assert_evaluation_is_concurrent();
                 assert_eq!(cx.get_tracked(&prev.result), evaluation_result.result);
             }
         }
diff --git a/compiler/rustc_type_ir/src/search_graph/mod.rs b/compiler/rustc_type_ir/src/search_graph/mod.rs
index 8f8f019510f..d7f91ef692c 100644
--- a/compiler/rustc_type_ir/src/search_graph/mod.rs
+++ b/compiler/rustc_type_ir/src/search_graph/mod.rs
@@ -53,7 +53,7 @@ pub trait Cx: Copy {
 
     fn with_global_cache<R>(self, f: impl FnOnce(&mut GlobalCache<Self>) -> R) -> R;
 
-    fn evaluation_is_concurrent(&self) -> bool;
+    fn assert_evaluation_is_concurrent(&self);
 }
 
 pub trait Delegate: Sized {