1 files changed, 32 insertions, 26 deletions

diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index ffddf6f73aa..697852c5ed3 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -2154,11 +2154,15 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 span_bug!(span, "use of bare `static` ConstArgKind::Path's not yet supported")
             }
             // FIXME(const_generics): create real const to allow fn items as const paths
-            Res::Def(DefKind::Fn | DefKind::AssocFn, _) => ty::Const::new_error_with_message(
-                tcx,
-                span,
-                "fn items cannot be used as const args",
-            ),
+            Res::Def(DefKind::Fn | DefKind::AssocFn, did) => {
+                self.dcx().span_delayed_bug(span, "function items cannot be used as const args");
+                let args = self.lower_generic_args_of_path_segment(
+                    span,
+                    did,
+                    path.segments.last().unwrap(),
+                );
+                ty::Const::new_value(tcx, ty::ValTree::zst(), Ty::new_fn_def(tcx, did, args))
+            }
 
             // Exhaustive match to be clear about what exactly we're considering to be
             // an invalid Res for a const path.
@@ -2557,27 +2561,29 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         // reject function types that violate cmse ABI requirements
         cmse::validate_cmse_abi(self.tcx(), self.dcx(), hir_id, abi, bare_fn_ty);
 
-        // Find any late-bound regions declared in return type that do
-        // not appear in the arguments. These are not well-formed.
-        //
-        // Example:
-        //     for<'a> fn() -> &'a str <-- 'a is bad
-        //     for<'a> fn(&'a String) -> &'a str <-- 'a is ok
-        let inputs = bare_fn_ty.inputs();
-        let late_bound_in_args =
-            tcx.collect_constrained_late_bound_regions(inputs.map_bound(|i| i.to_owned()));
-        let output = bare_fn_ty.output();
-        let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(output);
-
-        self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
-            struct_span_code_err!(
-                self.dcx(),
-                decl.output.span(),
-                E0581,
-                "return type references {}, which is not constrained by the fn input types",
-                br_name
-            )
-        });
+        if !bare_fn_ty.references_error() {
+            // Find any late-bound regions declared in return type that do
+            // not appear in the arguments. These are not well-formed.
+            //
+            // Example:
+            //     for<'a> fn() -> &'a str <-- 'a is bad
+            //     for<'a> fn(&'a String) -> &'a str <-- 'a is ok
+            let inputs = bare_fn_ty.inputs();
+            let late_bound_in_args =
+                tcx.collect_constrained_late_bound_regions(inputs.map_bound(|i| i.to_owned()));
+            let output = bare_fn_ty.output();
+            let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(output);
+
+            self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
+                struct_span_code_err!(
+                    self.dcx(),
+                    decl.output.span(),
+                    E0581,
+                    "return type references {}, which is not constrained by the fn input types",
+                    br_name
+                )
+            });
+        }
 
         bare_fn_ty
     }