Auto merge of #100982 - fee1-dead-contrib:const-impl-requires-const-trait, r=oli-obk

Require `#[const_trait]` on `Trait` for `impl const Trait`

r? `@oli-obk`

1 files changed, 6 insertions, 0 deletions

diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index c51debdc863..d03f0369648 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -428,12 +428,18 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
             }
 
             if let ty::FnDef(def_id, substs) = *constant.literal.ty().kind() {
+                // const_trait_impl: use a non-const param env when checking that a FnDef type is well formed.
+                // this is because the well-formedness of the function does not need to be proved to have `const`
+                // impls for trait bounds.
                 let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
+                let prev = self.cx.param_env;
+                self.cx.param_env = prev.without_const();
                 self.cx.normalize_and_prove_instantiated_predicates(
                     def_id,
                     instantiated_predicates,
                     locations,
                 );
+                self.cx.param_env = prev;
             }
         }
     }