From 6fdb54d2f103dc21197037e6b1ad0b51073b9627 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Sun, 8 Jan 2023 22:27:13 +0000
Subject: [PATCH] Do not emit structured suggestion for turbofish with wrong
 span

Fix #79161.
---
 compiler/rustc_parse/src/parser/diagnostics.rs | 12 ++++++++++--
 src/test/ui/parser/nested-bad-turbofish.rs     |  3 +++
 src/test/ui/parser/nested-bad-turbofish.stderr | 11 +++++++++++
 3 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100644 src/test/ui/parser/nested-bad-turbofish.rs
 create mode 100644 src/test/ui/parser/nested-bad-turbofish.stderr

diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index b3231f55bc6..d9fa3e31db9 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -1104,7 +1104,11 @@ pub(super) fn check_no_chained_comparison(
                     return if token::ModSep == self.token.kind {
                         // We have some certainty that this was a bad turbofish at this point.
                         // `foo< bar >::`
-                        err.suggest_turbofish = Some(op.span.shrink_to_lo());
+                        if let ExprKind::Binary(o, ..) = inner_op.kind && o.node == BinOpKind::Lt {
+                            err.suggest_turbofish = Some(op.span.shrink_to_lo());
+                        } else {
+                            err.help_turbofish = Some(());
+                        }
 
                         let snapshot = self.create_snapshot_for_diagnostic();
                         self.bump(); // `::`
@@ -1130,7 +1134,11 @@ pub(super) fn check_no_chained_comparison(
                     } else if token::OpenDelim(Delimiter::Parenthesis) == self.token.kind {
                         // We have high certainty that this was a bad turbofish at this point.
                         // `foo< bar >(`
-                        err.suggest_turbofish = Some(op.span.shrink_to_lo());
+                        if let ExprKind::Binary(o, ..) = inner_op.kind && o.node == BinOpKind::Lt {
+                            err.suggest_turbofish = Some(op.span.shrink_to_lo());
+                        } else {
+                            err.help_turbofish = Some(());
+                        }
                         // Consume the fn call arguments.
                         match self.consume_fn_args() {
                             Err(()) => Err(err.into_diagnostic(&self.sess.span_diagnostic)),
diff --git a/src/test/ui/parser/nested-bad-turbofish.rs b/src/test/ui/parser/nested-bad-turbofish.rs
new file mode 100644
index 00000000000..02099fde212
--- /dev/null
+++ b/src/test/ui/parser/nested-bad-turbofish.rs
@@ -0,0 +1,3 @@
+fn main() {
+    foo<<S as T>::V>(); //~ ERROR
+}
diff --git a/src/test/ui/parser/nested-bad-turbofish.stderr b/src/test/ui/parser/nested-bad-turbofish.stderr
new file mode 100644
index 00000000000..d82fa80e594
--- /dev/null
+++ b/src/test/ui/parser/nested-bad-turbofish.stderr
@@ -0,0 +1,11 @@
+error: comparison operators cannot be chained
+  --> $DIR/nested-bad-turbofish.rs:2:16
+   |
+LL |     foo<<S as T>::V>();
+   |                ^   ^
+   |
+   = help: use `::<...>` instead of `<...>` to specify lifetime, type, or const arguments
+   = help: or use `(...)` if you meant to specify fn arguments
+
+error: aborting due to previous error
+