From dbc2cc8717dd8c8006595d9e9c91ad472109165a Mon Sep 17 00:00:00 2001
From: lcnr <rust@lcnr.de>
Date: Mon, 2 Oct 2023 13:15:29 +0200
Subject: [PATCH] `skip_binder` to `instantiate_identity`

---
 compiler/rustc_middle/src/ty/instance.rs | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_middle/src/ty/instance.rs b/compiler/rustc_middle/src/ty/instance.rs
index 0b0a708e42bb9..0a425be52ffb5 100644
--- a/compiler/rustc_middle/src/ty/instance.rs
+++ b/compiler/rustc_middle/src/ty/instance.rs
@@ -617,12 +617,17 @@ impl<'tcx> Instance<'tcx> {
         v: EarlyBinder<T>,
     ) -> Result<T, NormalizationError<'tcx>>
     where
-        T: TypeFoldable<TyCtxt<'tcx>> + Clone,
+        T: TypeFoldable<TyCtxt<'tcx>>,
     {
         if let Some(args) = self.args_for_mir_body() {
             tcx.try_instantiate_and_normalize_erasing_regions(args, param_env, v)
         } else {
-            tcx.try_normalize_erasing_regions(param_env, v.skip_binder())
+            // We're using `instantiate_identity` as e.g.
+            // `FnPtrShim` is separately generated for every
+            // instantiation of the `FnDef`, so the MIR body
+            // is already instantiated. Any generic parameters it
+            // contains are generic parameters from the caller.
+            tcx.try_normalize_erasing_regions(param_env, v.instantiate_identity())
         }
     }