From 98a157aec8b08729249aa9ca78f9703aa3a4f279 Mon Sep 17 00:00:00 2001
From: zakrad <49591476+zakrad@users.noreply.github.com>
Date: Mon, 31 Aug 2026 13:21:07 +0330
Subject: [PATCH 1/2] Add test for the fn item uniqueness note with late bound
 lifetimes

---
 .../fn/fn-item-type-note-late-bound-145558.rs | 19 ++++++++++++++++++
 ...fn-item-type-note-late-bound-145558.stderr | 20 +++++++++++++++++++
 2 files changed, 39 insertions(+)
 create mode 100644 tests/ui/fn/fn-item-type-note-late-bound-145558.rs
 create mode 100644 tests/ui/fn/fn-item-type-note-late-bound-145558.stderr

diff --git a/tests/ui/fn/fn-item-type-note-late-bound-145558.rs b/tests/ui/fn/fn-item-type-note-late-bound-145558.rs
new file mode 100644
index 0000000000000..2463e2ba70675
--- /dev/null
+++ b/tests/ui/fn/fn-item-type-note-late-bound-145558.rs
@@ -0,0 +1,19 @@
+//! Regression test for https://github.com/rust-lang/rust/issues/145558
+//!
+//! The note explaining that distinct fn items have distinct types was suppressed when the
+//! signatures contained a late-bound lifetime, because the two binders name their bound
+//! region differently.
+
+//@ dont-require-annotations: NOTE
+
+struct A;
+
+fn f1<'a>(_: &'a A) {}
+fn f2<'a>(_: &'a A) {}
+
+fn main() {
+    let mut map = vec![];
+    map.push(f1);
+    map.push(f2);
+    //~^ ERROR mismatched types
+}
diff --git a/tests/ui/fn/fn-item-type-note-late-bound-145558.stderr b/tests/ui/fn/fn-item-type-note-late-bound-145558.stderr
new file mode 100644
index 0000000000000..31d773c7e4a79
--- /dev/null
+++ b/tests/ui/fn/fn-item-type-note-late-bound-145558.stderr
@@ -0,0 +1,20 @@
+error[E0308]: mismatched types
+  --> $DIR/fn-item-type-note-late-bound-145558.rs:17:14
+   |
+LL |     map.push(f1);
+   |     ---      -- this argument has type `for<'a> fn(&'a A) {f1}`...
+   |     |
+   |     ... which causes `map` to have type `Vec<for<'a> fn(&'a A) {f1}>`
+LL |     map.push(f2);
+   |         ---- ^^ expected fn item, found a different fn item
+   |         |
+   |         arguments to this method are incorrect
+   |
+   = note: expected fn item `for<'a> fn(&'a A) {f1}`
+              found fn item `for<'a> fn(&'a A) {f2}`
+note: method defined here
+  --> $SRC_DIR/alloc/src/vec/mod.rs:LL:COL
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.

From 21228c2dfa1a8afda35130d0fd59979ed6c34937 Mon Sep 17 00:00:00 2001
From: zakrad <49591476+zakrad@users.noreply.github.com>
Date: Mon, 31 Aug 2026 13:23:02 +0330
Subject: [PATCH 2/2] Do not suppress the fn item uniqueness note for late
 bound lifetimes

---
 .../src/error_reporting/infer/suggest.rs                      | 4 +++-
 tests/ui/fn/fn-item-type-note-late-bound-145558.rs            | 1 +
 tests/ui/fn/fn-item-type-note-late-bound-145558.stderr        | 1 +
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs
index db852701051cf..577571196a239 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs
@@ -521,7 +521,9 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 let found_sig =
                     self.normalize_fn_sig(self.tcx.fn_sig(*did2).instantiate(self.tcx, args2));
 
-                if self.same_type_modulo_infer(expected_sig, found_sig) {
+                let expected_sig_anon = self.tcx.anonymize_bound_vars(expected_sig);
+                let found_sig_anon = self.tcx.anonymize_bound_vars(found_sig);
+                if self.same_type_modulo_infer(expected_sig_anon, found_sig_anon) {
                     diag.subdiagnostic(FnUniqTypes);
                 }
 
diff --git a/tests/ui/fn/fn-item-type-note-late-bound-145558.rs b/tests/ui/fn/fn-item-type-note-late-bound-145558.rs
index 2463e2ba70675..3e8fc0e8b14a7 100644
--- a/tests/ui/fn/fn-item-type-note-late-bound-145558.rs
+++ b/tests/ui/fn/fn-item-type-note-late-bound-145558.rs
@@ -16,4 +16,5 @@ fn main() {
     map.push(f1);
     map.push(f2);
     //~^ ERROR mismatched types
+    //~| NOTE different fn items have unique types
 }
diff --git a/tests/ui/fn/fn-item-type-note-late-bound-145558.stderr b/tests/ui/fn/fn-item-type-note-late-bound-145558.stderr
index 31d773c7e4a79..bf0a1c3316e57 100644
--- a/tests/ui/fn/fn-item-type-note-late-bound-145558.stderr
+++ b/tests/ui/fn/fn-item-type-note-late-bound-145558.stderr
@@ -12,6 +12,7 @@ LL |     map.push(f2);
    |
    = note: expected fn item `for<'a> fn(&'a A) {f1}`
               found fn item `for<'a> fn(&'a A) {f2}`
+   = note: different fn items have unique types, even if their signatures are the same
 note: method defined here
   --> $SRC_DIR/alloc/src/vec/mod.rs:LL:COL