From 06a1e8854c95d5be5db0bebe4630c691b604e792 Mon Sep 17 00:00:00 2001
From: Jack Huey <31162821+jackh726@users.noreply.github.com>
Date: Tue, 10 May 2022 22:40:43 -0400
Subject: [PATCH] Add rustc_on_unimplemented to Subst

---
 compiler/rustc_middle/src/ty/subst.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/compiler/rustc_middle/src/ty/subst.rs b/compiler/rustc_middle/src/ty/subst.rs
index 9053d744415..48c71113d50 100644
--- a/compiler/rustc_middle/src/ty/subst.rs
+++ b/compiler/rustc_middle/src/ty/subst.rs
@@ -499,6 +499,7 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<Ty<'tcx>> {
 }
 
 // Just call `foo.subst(tcx, substs)` to perform a substitution across `foo`.
+#[rustc_on_unimplemented(message = "Calling `subst` must now be done through an `EarlyBinder`")]
 pub trait Subst<'tcx>: Sized {
     type Inner;