From f65810a7ee9cbc71a13032866452c41f455228e9 Mon Sep 17 00:00:00 2001
From: Chao Shi <stepinto@live.com>
Date: Sat, 13 Sep 2025 20:02:14 +0800
Subject: [PATCH] Fix issue #41 handle return statement inside closure

We should never replace return statements to `break 'run` inside
closures.  Refer to test case `gl_issue_41` for an example.
---
 src/implementation/codegen.rs |  6 +++++-
 tests/issues.rs               | 22 ++++++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/implementation/codegen.rs b/src/implementation/codegen.rs
index e94956f..34dcb1d 100644
--- a/src/implementation/codegen.rs
+++ b/src/implementation/codegen.rs
@@ -8,7 +8,7 @@ use syn::{
     spanned::Spanned,
     visit::{visit_return_type, Visit},
     visit_mut::{self as visitor, visit_block_mut, visit_expr_mut, VisitMut},
-    Attribute, Expr, ExprCall, ReturnType, TypeImplTrait,
+    Attribute, Expr, ExprCall, ExprClosure, ReturnType, TypeImplTrait,
 };
 
 use crate::implementation::{Contract, ContractMode, ContractType, FuncWithContracts};
@@ -379,6 +379,10 @@ impl VisitMut for ReturnReplacer {
 
         visit_expr_mut(self, node);
     }
+
+    fn visit_expr_closure_mut(&mut self, _node: &mut ExprClosure) {
+        // Do not replace return statements inside closures.  Skip calling the base visitor.
+    }
 }
 
 struct ImplDetector {
diff --git a/tests/issues.rs b/tests/issues.rs
index 043cac2..36449f1 100644
--- a/tests/issues.rs
+++ b/tests/issues.rs
@@ -96,3 +96,25 @@ fn gl_issue_18() {
 
     assert_eq!(1, euclidean(3, 4));
 }
+
+#[allow(unused)] // compile-only test
+#[test]
+fn gl_issue_41() {
+    use contracts::requires;
+
+    fn foo(f: impl Fn(i32) -> i32) -> i32 {
+        // no-op
+        f(-10)
+    }
+
+    #[requires(true)]
+    fn bar() {
+        let y = foo(|x: i32| {
+            if x < 0 {
+                return 0;
+            }
+            x
+        });
+        assert_eq!(y, 0);
+    }
+}