From 7724ba7bd5f2c947a7dc561c24b19bb8409a6ed6 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sat, 13 Jan 2024 21:53:42 +0000
Subject: [PATCH] assert that trait solver is only created in proper infcx

---
 compiler/rustc_trait_selection/src/solve/fulfill.rs  | 5 +++++
 compiler/rustc_trait_selection/src/traits/fulfill.rs | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/compiler/rustc_trait_selection/src/solve/fulfill.rs b/compiler/rustc_trait_selection/src/solve/fulfill.rs
index 2139210b87364..09f4f3e9702ff 100644
--- a/compiler/rustc_trait_selection/src/solve/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/solve/fulfill.rs
@@ -36,6 +36,11 @@ pub struct FulfillmentCtxt<'tcx> {
 
 impl<'tcx> FulfillmentCtxt<'tcx> {
     pub fn new(infcx: &InferCtxt<'tcx>) -> FulfillmentCtxt<'tcx> {
+        assert!(
+            infcx.next_trait_solver(),
+            "new trait solver fulfillment context created when \
+            infcx is set up for old trait solver"
+        );
         FulfillmentCtxt { obligations: Vec::new(), usable_in_snapshot: infcx.num_open_snapshots() }
     }
 }
diff --git a/compiler/rustc_trait_selection/src/traits/fulfill.rs b/compiler/rustc_trait_selection/src/traits/fulfill.rs
index 045d7e444b6e8..472342f98980d 100644
--- a/compiler/rustc_trait_selection/src/traits/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/fulfill.rs
@@ -80,6 +80,11 @@ static_assert_size!(PendingPredicateObligation<'_>, 72);
 impl<'tcx> FulfillmentContext<'tcx> {
     /// Creates a new fulfillment context.
     pub(super) fn new(infcx: &InferCtxt<'tcx>) -> FulfillmentContext<'tcx> {
+        assert!(
+            !infcx.next_trait_solver(),
+            "old trait solver fulfillment context created when \
+            infcx is set up for new trait solver"
+        );
         FulfillmentContext {
             predicates: ObligationForest::new(),
             usable_in_snapshot: infcx.num_open_snapshots(),