From 58018d438b3e14624bf33a9c0d2031e906797b8d Mon Sep 17 00:00:00 2001
From: Santiago Pastorino <spastorino@gmail.com>
Date: Tue, 20 Oct 2020 13:23:58 -0300
Subject: [PATCH] Properly restore within_fn_param value to the previous state

---
 compiler/rustc_typeck/src/check/gather_locals.rs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_typeck/src/check/gather_locals.rs b/compiler/rustc_typeck/src/check/gather_locals.rs
index d5e45c3b89f31..8699de4ce14cd 100644
--- a/compiler/rustc_typeck/src/check/gather_locals.rs
+++ b/compiler/rustc_typeck/src/check/gather_locals.rs
@@ -6,6 +6,7 @@ use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKi
 use rustc_middle::ty::Ty;
 use rustc_span::Span;
 use rustc_trait_selection::traits;
+use std::mem;
 
 pub(super) struct GatherLocalsVisitor<'a, 'tcx> {
     fcx: &'a FnCtxt<'a, 'tcx>,
@@ -97,9 +98,9 @@ impl<'a, 'tcx> Visitor<'tcx> for GatherLocalsVisitor<'a, 'tcx> {
     }
 
     fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
-        self.within_fn_param = true;
+        let old_within_fn_param = mem::replace(&mut self.within_fn_param, true);
         intravisit::walk_param(self, param);
-        self.within_fn_param = false;
+        self.within_fn_param = old_within_fn_param;
     }
 
     // Add pattern bindings.