From b7546150b2f372bc31f908c41c0078936c3d8b66 Mon Sep 17 00:00:00 2001
From: "Zack M. Davis" <code@zackmdavis.net>
Date: Sat, 27 Oct 2018 14:55:07 -0700
Subject: [PATCH] back out bogus `Ok`-wrapping suggestion on `?` arm type
 mismatch

This suggestion was introduced in #51938 / 6cc78bf8d7 (while
introducing different language for type errors coming from `?` rather
than a `match`), but it has a lot of false-positives (as repeatedly
reported in Issues #52537, #52598, #54578, #55336), and incorrect
suggestions carry more badness than marginal good suggestions do
goodness. Just get rid of it (unless and until someone figures out how
to do it correctly).

Resolves #52537, resolves #54578.
---
 src/librustc/infer/error_reporting/mod.rs     | 12 +--------
 ...51632-try-desugar-incompatible-types.fixed | 25 -------------------
 ...ue-51632-try-desugar-incompatible-types.rs |  3 ---
 ...1632-try-desugar-incompatible-types.stderr |  7 ++----
 4 files changed, 3 insertions(+), 44 deletions(-)
 delete mode 100644 src/test/ui/issues/issue-51632-try-desugar-incompatible-types.fixed

diff --git a/src/librustc/infer/error_reporting/mod.rs b/src/librustc/infer/error_reporting/mod.rs
index 8b4669c89fe..d19c495af3b 100644
--- a/src/librustc/infer/error_reporting/mod.rs
+++ b/src/librustc/infer/error_reporting/mod.rs
@@ -479,17 +479,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                         err.span_label(arm_span, msg);
                     }
                 }
-                hir::MatchSource::TryDesugar => {
-                    // Issue #51632
-                    if let Ok(try_snippet) = self.tcx.sess.source_map().span_to_snippet(arm_span) {
-                        err.span_suggestion_with_applicability(
-                            arm_span,
-                            "try wrapping with a success variant",
-                            format!("Ok({})", try_snippet),
-                            Applicability::MachineApplicable,
-                        );
-                    }
-                }
+                hir::MatchSource::TryDesugar => {}
                 _ => {
                     let msg = "match arm with an incompatible type";
                     if self.tcx.sess.source_map().is_multiline(arm_span) {
diff --git a/src/test/ui/issues/issue-51632-try-desugar-incompatible-types.fixed b/src/test/ui/issues/issue-51632-try-desugar-incompatible-types.fixed
deleted file mode 100644
index 016cff914bd..00000000000
--- a/src/test/ui/issues/issue-51632-try-desugar-incompatible-types.fixed
+++ /dev/null
@@ -1,25 +0,0 @@
-// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-// run-rustfix
-
-#![allow(dead_code)]
-
-fn missing_discourses() -> Result<isize, ()> {
-    Ok(1)
-}
-
-fn forbidden_narratives() -> Result<isize, ()> {
-    Ok(missing_discourses()?)
-    //~^ ERROR try expression alternatives have incompatible types
-    //~| HELP try wrapping with a success variant
-}
-
-fn main() {}
diff --git a/src/test/ui/issues/issue-51632-try-desugar-incompatible-types.rs b/src/test/ui/issues/issue-51632-try-desugar-incompatible-types.rs
index 315773a85f0..32ea715b64f 100644
--- a/src/test/ui/issues/issue-51632-try-desugar-incompatible-types.rs
+++ b/src/test/ui/issues/issue-51632-try-desugar-incompatible-types.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// run-rustfix
-
 #![allow(dead_code)]
 
 fn missing_discourses() -> Result<isize, ()> {
@@ -19,7 +17,6 @@ fn missing_discourses() -> Result<isize, ()> {
 fn forbidden_narratives() -> Result<isize, ()> {
     missing_discourses()?
     //~^ ERROR try expression alternatives have incompatible types
-    //~| HELP try wrapping with a success variant
 }
 
 fn main() {}
diff --git a/src/test/ui/issues/issue-51632-try-desugar-incompatible-types.stderr b/src/test/ui/issues/issue-51632-try-desugar-incompatible-types.stderr
index a50af5624c0..590cbff67a4 100644
--- a/src/test/ui/issues/issue-51632-try-desugar-incompatible-types.stderr
+++ b/src/test/ui/issues/issue-51632-try-desugar-incompatible-types.stderr
@@ -1,11 +1,8 @@
 error[E0308]: try expression alternatives have incompatible types
-  --> $DIR/issue-51632-try-desugar-incompatible-types.rs:20:5
+  --> $DIR/issue-51632-try-desugar-incompatible-types.rs:18:5
    |
 LL |     missing_discourses()?
-   |     ^^^^^^^^^^^^^^^^^^^^^
-   |     |
-   |     expected enum `std::result::Result`, found isize
-   |     help: try wrapping with a success variant: `Ok(missing_discourses()?)`
+   |     ^^^^^^^^^^^^^^^^^^^^^ expected enum `std::result::Result`, found isize
    |
    = note: expected type `std::result::Result<isize, ()>`
               found type `isize`