From a5d931050e69df1bc07117a2891154a71a06a73e Mon Sep 17 00:00:00 2001
From: Guanqun Lu <guanqun.lu@gmail.com>
Date: Tue, 24 Sep 2019 17:49:25 +0800
Subject: [PATCH] remove 'as_str' when it's already a str type.

fix #62642
---
 src/librustc_typeck/check/method/suggest.rs | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/librustc_typeck/check/method/suggest.rs b/src/librustc_typeck/check/method/suggest.rs
index 2d4d2e32f23..e68e3211cad 100644
--- a/src/librustc_typeck/check/method/suggest.rs
+++ b/src/librustc_typeck/check/method/suggest.rs
@@ -518,7 +518,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     }
                 }
 
-                if let Some(lev_candidate) = lev_candidate {
+                fn is_str_ref<'tcx>(ty: Ty<'tcx>) -> bool {
+                    match ty.sty {
+                        ty::Str => true,
+                        ty::Ref(_, ty, _) => is_str_ref(&ty),
+                        _ => false,
+                    }
+                }
+                if item_name.as_str() == "as_str" && is_str_ref(&actual) {
+                    err.span_suggestion(
+                        span,
+                        "try to remove `as_str`",
+                        String::new(),
+                        Applicability::MaybeIncorrect,
+                    );
+                } else if let Some(lev_candidate) = lev_candidate {
                     let def_kind = lev_candidate.def_kind();
                     err.span_suggestion(
                         span,