From 40dea088fdac5859cf841c60934a4c5fc52cbbf6 Mon Sep 17 00:00:00 2001
From: CreeperFace <165158232+dy-tea@users.noreply.github.com>
Date: Fri, 19 Dec 2025 12:54:28 +0000
Subject: [PATCH] checker: ensure fn pointer cannot be used as non-fn argument
 (fix #26017) (#26022)

---
 vlib/v/checker/checker.v                           |  6 ++++--
 .../tests/method_ptr_used_as_argument_err.out      | 14 ++++++++++++++
 .../tests/method_ptr_used_as_argument_err.vv       | 10 ++++++++++
 3 files changed, 28 insertions(+), 2 deletions(-)
 create mode 100644 vlib/v/checker/tests/method_ptr_used_as_argument_err.out
 create mode 100644 vlib/v/checker/tests/method_ptr_used_as_argument_err.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 042bcaa66..61d8db7c3 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1900,8 +1900,10 @@ fn (mut c Checker) selector_expr(mut node ast.SelectorExpr) ast.Type {
 	if mut method := c.table.sym(c.unwrap_generic(typ)).find_method_with_generic_parent(field_name) {
 		c.markused_comptime_call(typ.has_flag(.generic), '${int(method.params[0].typ)}.${field_name}')
 		if c.expected_type != 0 && c.expected_type != ast.none_type {
-			fn_type := ast.new_type(c.table.find_or_register_fn_type(method, false, true))
-			// if the expected type includes the receiver, don't hide it behind a closure
+			mut method_copy := method
+			method_copy.name = ''
+			fn_type := ast.new_type(c.table.find_or_register_fn_type(method_copy, false,
+				true))
 			if c.check_types(fn_type, c.expected_type) {
 				c.table.used_features.anon_fn = true
 				return fn_type
diff --git a/vlib/v/checker/tests/method_ptr_used_as_argument_err.out b/vlib/v/checker/tests/method_ptr_used_as_argument_err.out
new file mode 100644
index 000000000..a1936b6b3
--- /dev/null
+++ b/vlib/v/checker/tests/method_ptr_used_as_argument_err.out
@@ -0,0 +1,14 @@
+vlib/v/checker/tests/method_ptr_used_as_argument_err.vv:8:16: error: cannot use `fn () int` as `int` in argument 1 to `add`
+    6 |     arg1 := '10'
+    7 |     arg2 := '20'
+    8 |     result := add(arg1.int, arg2.int)
+      |                   ~~~~~~~~
+    9 |     println(result)
+   10 | }
+vlib/v/checker/tests/method_ptr_used_as_argument_err.vv:8:26: error: cannot use `fn () int` as `int` in argument 2 to `add`
+    6 |     arg1 := '10'
+    7 |     arg2 := '20'
+    8 |     result := add(arg1.int, arg2.int)
+      |                             ~~~~~~~~
+    9 |     println(result)
+   10 | }
diff --git a/vlib/v/checker/tests/method_ptr_used_as_argument_err.vv b/vlib/v/checker/tests/method_ptr_used_as_argument_err.vv
new file mode 100644
index 000000000..d0f082810
--- /dev/null
+++ b/vlib/v/checker/tests/method_ptr_used_as_argument_err.vv
@@ -0,0 +1,10 @@
+fn add(x int, y int) int {
+	return x + y
+}
+
+fn main() {
+	arg1 := '10'
+	arg2 := '20'
+	result := add(arg1.int, arg2.int)
+	println(result)
+}
-- 
2.39.5