From 068dfb9eb9fc5aa891a764caca07a02ca6b4dfe0 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Tue, 14 Apr 2026 22:56:59 +0300
Subject: [PATCH] checker: fix simple generic structure declaration error
 (fixes #21989)

---
 vlib/v/checker/checker.v                      |  6 ++++
 .../tests/generic_method_value_err.out        | 14 ++++++++++
 .../checker/tests/generic_method_value_err.vv | 28 +++++++++++++++++++
 3 files changed, 48 insertions(+)
 create mode 100644 vlib/v/checker/tests/generic_method_value_err.out
 create mode 100644 vlib/v/checker/tests/generic_method_value_err.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 792ea4779..a27a4cad6 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -3020,6 +3020,12 @@ fn (mut c Checker) selector_expr(mut node ast.SelectorExpr) ast.Type {
 		method.name = ''
 		fn_type := ast.new_type(c.table.find_or_register_fn_type(method, false, true))
 		node.typ = c.unwrap_generic(fn_type)
+		if c.type_has_unresolved_generic_parts(fn_type) {
+			c.error('cannot use `${node.expr}.${node.field_name}` as a generic function value',
+				node.pos)
+			c.table.used_features.anon_fn = true
+			return fn_type
+		}
 		c.table.used_features.anon_fn = true
 		return fn_type
 	}
diff --git a/vlib/v/checker/tests/generic_method_value_err.out b/vlib/v/checker/tests/generic_method_value_err.out
new file mode 100644
index 000000000..81a926aa2
--- /dev/null
+++ b/vlib/v/checker/tests/generic_method_value_err.out
@@ -0,0 +1,14 @@
+vlib/v/checker/tests/generic_method_value_err.vv:25:17: error: cannot use `TCount(4).take_part` as a generic function value
+   23 | 
+   24 | fn main() {
+   25 |     _ = [TCount(4).take_part]
+      |                    ~~~~~~~~~
+   26 |     f := TCount(4).print_part
+   27 |     _ = f
+vlib/v/checker/tests/generic_method_value_err.vv:26:17: error: cannot use `TCount(4).print_part` as a generic function value
+   24 | fn main() {
+   25 |     _ = [TCount(4).take_part]
+   26 |     f := TCount(4).print_part
+      |                    ~~~~~~~~~~
+   27 |     _ = f
+   28 | }
diff --git a/vlib/v/checker/tests/generic_method_value_err.vv b/vlib/v/checker/tests/generic_method_value_err.vv
new file mode 100644
index 000000000..4ea4b574c
--- /dev/null
+++ b/vlib/v/checker/tests/generic_method_value_err.vv
@@ -0,0 +1,28 @@
+module main
+
+struct ParserResult[I, O] {
+	i []I
+	o []O
+}
+
+type TCount = u32
+
+fn (count TCount) take_part[I, O](i []I) !ParserResult[I, O] {
+	if i.len < count {
+		return error('error1')
+	}
+	return ParserResult{
+		i: i[count..]
+		o: i[..count]
+	}
+}
+
+fn (count TCount) print_part[T](v T) {
+	_ = v
+}
+
+fn main() {
+	_ = [TCount(4).take_part]
+	f := TCount(4).print_part
+	_ = f
+}
-- 
2.39.5