From 04097e99df51d4edb08d61db9e3ceeff6943a9e9 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Sun, 26 Apr 2026 00:22:08 +0300
Subject: [PATCH] tests: interface_closure_test.v

---
 .../tests/interfaces/interface_closure_test.v | 58 +++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/vlib/v/tests/interfaces/interface_closure_test.v b/vlib/v/tests/interfaces/interface_closure_test.v
index 0784f584d..9a979853f 100644
--- a/vlib/v/tests/interfaces/interface_closure_test.v
+++ b/vlib/v/tests/interfaces/interface_closure_test.v
@@ -28,3 +28,61 @@ fn test_main() {
 	b.with_reader(a.caller)!
 	assert true
 }
+
+interface ClosureCommand {
+	value() int
+mut:
+	increment()
+}
+
+struct MutableClosureCommand {
+mut:
+	value_ int
+}
+
+fn (cmd MutableClosureCommand) value() int {
+	return cmd.value_
+}
+
+fn (mut cmd MutableClosureCommand) increment() {
+	cmd.value_++
+}
+
+fn with_closure_connection(func fn () !) ! {
+	func()!
+}
+
+fn with_closure_writer(func fn () !) ! {
+	func()!
+}
+
+fn with_closure_reader(func fn () !) ! {
+	func()!
+}
+
+fn write_closure_command(cmd ClosureCommand) ! {
+	assert cmd.value() == 41
+}
+
+fn read_closure_command(mut cmd ClosureCommand) ! {
+	cmd.increment()
+}
+
+fn process_closure_command(mut cmd ClosureCommand) ! {
+	with_closure_connection(fn [mut cmd] () ! {
+		with_closure_writer(fn [cmd] () ! {
+			write_closure_command(cmd)!
+		})!
+		with_closure_reader(fn [mut cmd] () ! {
+			read_closure_command(mut cmd)!
+		})!
+	})!
+}
+
+fn test_nested_closure_captures_mut_interface_by_value() {
+	mut cmd := ClosureCommand(MutableClosureCommand{
+		value_: 41
+	})
+	process_closure_command(mut cmd)!
+	assert cmd.value() == 42
+}
-- 
2.39.5