From 824f07f92b0e2aeedf69d99d3c7cd1039e0456a1 Mon Sep 17 00:00:00 2001
From: Adwin White <adwinw01@gmail.com>
Date: Sat, 29 Aug 2026 15:03:20 +0800
Subject: [PATCH] treat identity region constraint as true

---
 .../rustc_type_ir/src/region_constraint.rs    |  4 +++
 .../identity_region_outlives.rs               | 29 +++++++++++++++++++
 2 files changed, 33 insertions(+)
 create mode 100644 tests/ui/assumptions_on_binders/identity_region_outlives.rs

diff --git a/compiler/rustc_type_ir/src/region_constraint.rs b/compiler/rustc_type_ir/src/region_constraint.rs
index 2923709432ee5..1e4e7572c8551 100644
--- a/compiler/rustc_type_ir/src/region_constraint.rs
+++ b/compiler/rustc_type_ir/src/region_constraint.rs
@@ -681,6 +681,10 @@ fn pull_region_outlives_constraints_out_of_universe<
             constraint
         }
         RegionOutlives(region_1, region_2, ()) => {
+            if region_1 == region_2 {
+                return RegionConstraint::new_true();
+            }
+
             let region_1_u = max_universe(infcx, region_1);
             let region_2_u = max_universe(infcx, region_2);
 
diff --git a/tests/ui/assumptions_on_binders/identity_region_outlives.rs b/tests/ui/assumptions_on_binders/identity_region_outlives.rs
new file mode 100644
index 0000000000000..b12c7d4909945
--- /dev/null
+++ b/tests/ui/assumptions_on_binders/identity_region_outlives.rs
@@ -0,0 +1,29 @@
+//@ compile-flags: -Zassumptions-on-binders
+//@ check-pass
+
+// Regression test for #161733.
+// Previously we didn't properly handle identity region outlives
+// and it was mistakenly considered as false region constraint.
+// The closure is needed to register the type outlives obligation
+// in borrowck.
+
+#![feature(test_binder_constraints)]
+
+fn foo<T>()
+where
+    for<'a> &'a T: 'a,
+{
+    || {};
+}
+
+core::test_binder_constraints! {
+    impl<T> {
+        forall<'a> where T: 'a {
+            'a: 'a,
+            T: 'a,
+        } expect {
+        }
+    }
+}
+
+fn main() {}