Add assert to check if tcx.sess has errors

This checks when trait bounds are introduced if the tcx.session has errors, not sure if this
where the problem could come from but might as well look

src/librustc_traits/chalk/db.rs

@@ -560,12 +560,14 @@ fn bound_vars_for_item(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
             ))
             .into(),
 
-        ty::GenericParamDefKind::Const => tcx
-            .mk_const(ty::Const {
+        ty::GenericParamDefKind::Const => {
+            assert!(!tcx.sess.has_errors());
+            tcx.mk_const(ty::Const {
                 val: ty::ConstKind::Bound(ty::INNERMOST, ty::BoundVar::from(param.index)),
                 ty: tcx.type_of(param.def_id),
             })
-            .into(),
+            .into()
+        }
     })
 }
 

src/test/ui/const-generics/issue-74634.rs

@@ -0,0 +1,25 @@
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+trait If<const COND: bool> {}
+impl If<true> for () {}
+
+trait IsZero<const N: u8> {
+    type Answer;
+}
+
+struct True;
+struct False;
+
+impl<const N: u8> IsZero<N> for ()
+where (): If<{N == 0}> {
+    type Answer = True;
+}
+
+trait Foobar<const N: u8> {}
+
+impl<const N: u8> Foobar<N> for ()
+where (): IsZero<N, Answer = True> {}
+
+impl<const N: u8> Foobar<N> for ()
+where (): IsZero<N, Answer = False> {}