From 91a43f04237dc9fe839fe8466d459e4f215d02fc Mon Sep 17 00:00:00 2001
From: Rob Pilling <robpilling@gmail.com>
Date: Fri, 28 Jan 2022 23:17:47 +0000
Subject: [PATCH] Only suggest 1-tuple if expected and found types match

---
 .../src/infer/error_reporting/mod.rs          | 46 +++++++++++--------
 src/test/ui/typeck/issue-84768.stderr         |  4 --
 2 files changed, 27 insertions(+), 23 deletions(-)

diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 71a81d12839..c16181aab04 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -2044,26 +2044,34 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         // If a tuple of length one was expected and the found expression has
                         // parentheses around it, perhaps the user meant to write `(expr,)` to
                         // build a tuple (issue #86100)
-                        (ty::Tuple(_), _) if expected.tuple_fields().count() == 1 => {
-                            if let Ok(code) = self.tcx.sess().source_map().span_to_snippet(span) {
-                                if code.starts_with('(') && code.ends_with(')') {
-                                    let before_close = span.hi() - BytePos::from_u32(1);
+                        (ty::Tuple(_), _) => {
+                            if let [expected_tup_elem] =
+                                expected.tuple_fields().collect::<Vec<_>>()[..]
+                            {
+                                if same_type_modulo_infer(expected_tup_elem, found) {
+                                    if let Ok(code) =
+                                        self.tcx.sess().source_map().span_to_snippet(span)
+                                    {
+                                        if code.starts_with('(') && code.ends_with(')') {
+                                            let before_close = span.hi() - BytePos::from_u32(1);
 
-                                    err.span_suggestion(
-                                        span.with_hi(before_close).shrink_to_hi(),
-                                        "use a trailing comma to create a tuple with one element",
-                                        ",".into(),
-                                        Applicability::MaybeIncorrect,
-                                    );
-                                } else {
-                                    err.multipart_suggestion(
-                                        "use a trailing comma to create a tuple with one element",
-                                        vec![
-                                            (span.shrink_to_lo(), "(".into()),
-                                            (span.shrink_to_hi(), ",)".into()),
-                                        ],
-                                        Applicability::MaybeIncorrect,
-                                    );
+                                            err.span_suggestion(
+                                                span.with_hi(before_close).shrink_to_hi(),
+                                                "use a trailing comma to create a tuple with one element",
+                                                ",".into(),
+                                                Applicability::MaybeIncorrect,
+                                            );
+                                        } else {
+                                            err.multipart_suggestion(
+                                                "use a trailing comma to create a tuple with one element",
+                                                vec![
+                                                    (span.shrink_to_lo(), "(".into()),
+                                                    (span.shrink_to_hi(), ",)".into()),
+                                                ],
+                                                Applicability::MaybeIncorrect,
+                                            );
+                                        }
+                                    }
                                 }
                             }
                         }
diff --git a/src/test/ui/typeck/issue-84768.stderr b/src/test/ui/typeck/issue-84768.stderr
index 331aa25c7a3..0a79d539ea9 100644
--- a/src/test/ui/typeck/issue-84768.stderr
+++ b/src/test/ui/typeck/issue-84768.stderr
@@ -12,10 +12,6 @@ LL |     <F as FnOnce(&mut u8)>::call_once(f, 1)
    |
    = note: expected tuple `(&mut u8,)`
                found type `{integer}`
-help: use a trailing comma to create a tuple with one element
-   |
-LL |     <F as FnOnce(&mut u8)>::call_once(f, (1,))
-   |                                          + ++
 
 error: aborting due to 2 previous errors