From 5f401e3ce6bf4f5b112204e217fdfa47e8a5a65b Mon Sep 17 00:00:00 2001
From: Shoyu Vanilla <modulo641@gmail.com>
Date: Thu, 19 Jun 2025 01:30:10 +0900
Subject: [PATCH] fix: Closure capturing for let exprs

---
 crates/hir-ty/src/infer/closure.rs            |  6 +++++-
 crates/hir-ty/src/tests/closure_captures.rs   | 19 +++++++++++++++++++
 .../src/handlers/moved_out_of_ref.rs          | 19 +++++++++++++++++++
 3 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/crates/hir-ty/src/infer/closure.rs b/crates/hir-ty/src/infer/closure.rs
index d1432cacf8..b756bb859d 100644
--- a/crates/hir-ty/src/infer/closure.rs
+++ b/crates/hir-ty/src/infer/closure.rs
@@ -1230,11 +1230,15 @@ impl InferenceContext<'_> {
                     self.select_from_expr(*expr);
                 }
             }
+            Expr::Let { pat: _, expr } => {
+                self.walk_expr(*expr);
+                let place = self.place_of_expr(*expr);
+                self.ref_expr(*expr, place);
+            }
             Expr::UnaryOp { expr, op: _ }
             | Expr::Array(Array::Repeat { initializer: expr, repeat: _ })
             | Expr::Await { expr }
             | Expr::Loop { body: expr, label: _ }
-            | Expr::Let { pat: _, expr }
             | Expr::Box { expr }
             | Expr::Cast { expr, type_ref: _ } => {
                 self.consume_expr(*expr);
diff --git a/crates/hir-ty/src/tests/closure_captures.rs b/crates/hir-ty/src/tests/closure_captures.rs
index 88d21be81e..7fb981752d 100644
--- a/crates/hir-ty/src/tests/closure_captures.rs
+++ b/crates/hir-ty/src/tests/closure_captures.rs
@@ -444,3 +444,22 @@ fn main() {
         expect!["99..165;49..54;120..121,133..134 ByRef(Mut { kind: Default }) a &'? mut A"],
     );
 }
+
+#[test]
+fn let_binding_is_a_ref_capture() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct S;
+fn main() {
+    let mut s = S;
+    let s_ref = &mut s;
+    let closure = || {
+        if let ref cb = s_ref {
+        }
+    };
+}
+"#,
+        expect!["83..135;49..54;112..117 ByRef(Shared) s_ref &'? &'? mut S"],
+    );
+}
diff --git a/crates/ide-diagnostics/src/handlers/moved_out_of_ref.rs b/crates/ide-diagnostics/src/handlers/moved_out_of_ref.rs
index 7181d708fe..0928262d22 100644
--- a/crates/ide-diagnostics/src/handlers/moved_out_of_ref.rs
+++ b/crates/ide-diagnostics/src/handlers/moved_out_of_ref.rs
@@ -220,4 +220,23 @@ fn test() {
             "#,
         )
     }
+
+    #[test]
+    fn regression_18201() {
+        check_diagnostics(
+            r#"
+//- minicore: copy
+struct NotCopy;
+struct S(NotCopy);
+impl S {
+    fn f(&mut self) {
+        || {
+            if let ref mut _cb = self.0 {
+            }
+        };
+    }
+}
+"#,
+        )
+    }
 }