From 73f3dce5c7a81f23f2ae8ec7bf085237d431aca5 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 25 Mar 2026 16:42:19 +0300
Subject: [PATCH] checker: fix cannot match generic type in generic function
 (fixes #24648)

---
 vlib/v/checker/checker.v                      | 24 ++++++++++++++++++-
 ...eneric_match_generic_interface_type_test.v | 21 ++++++++++++++++
 2 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/generics/generic_match_generic_interface_type_test.v

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 56a761816..d8ac3368f 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1730,6 +1730,28 @@ fn (mut c Checker) fail_if_immutable(mut expr ast.Expr) (string, token.Pos) {
 	return to_lock, pos
 }
 
+fn (mut c Checker) unwrap_generic_concrete_type(typ ast.Type) ast.Type {
+	utyp := c.unwrap_generic(typ)
+	if !c.needs_unwrap_generic_type(typ) || c.table.sym(utyp).kind != .placeholder {
+		return utyp
+	}
+	if c.inside_generic_struct_init {
+		generic_names := c.cur_struct_generic_types.map(c.table.sym(it).name)
+		return c.table.unwrap_generic_type(typ, generic_names, c.cur_struct_concrete_types)
+	}
+	if c.table.cur_fn != unsafe { nil } {
+		resolved := c.table.unwrap_generic_type(typ, c.table.cur_fn.generic_names, c.table.cur_concrete_types)
+		if c.table.sym(resolved).kind != .placeholder {
+			return resolved
+		}
+		if c.inside_lambda && c.table.cur_lambda.call_ctx != unsafe { nil } {
+			return c.table.unwrap_generic_type(typ, c.table.cur_lambda.func.decl.generic_names,
+				c.table.cur_lambda.call_ctx.concrete_types)
+		}
+	}
+	return utyp
+}
+
 fn (mut c Checker) type_implements(typ ast.Type, interface_type ast.Type, pos token.Pos) bool {
 	mut resolved_interface_type := c.unwrap_generic(interface_type)
 	if typ == resolved_interface_type {
@@ -1738,7 +1760,7 @@ fn (mut c Checker) type_implements(typ ast.Type, interface_type ast.Type, pos to
 	$if debug_interface_type_implements ? {
 		eprintln('> type_implements typ: ${typ.debug()} (`${c.table.type_to_str(typ)}`) | inter_typ: ${resolved_interface_type.debug()} (`${c.table.type_to_str(resolved_interface_type)}`)')
 	}
-	utyp := c.unwrap_generic(typ)
+	utyp := c.unwrap_generic_concrete_type(typ)
 	styp := c.table.type_to_str(utyp)
 	typ_sym := c.table.sym(utyp)
 	mut inter_sym := c.table.final_sym(resolved_interface_type)
diff --git a/vlib/v/tests/generics/generic_match_generic_interface_type_test.v b/vlib/v/tests/generics/generic_match_generic_interface_type_test.v
new file mode 100644
index 000000000..34f3e97fa
--- /dev/null
+++ b/vlib/v/tests/generics/generic_match_generic_interface_type_test.v
@@ -0,0 +1,21 @@
+interface Named {
+	get_name() string
+}
+
+struct GenericValue[T] implements Named {}
+
+fn (g GenericValue[T]) get_name() string {
+	return T.name
+}
+
+fn is_match[T](base Named) bool {
+	match base {
+		GenericValue[T] { return true }
+		else { return false }
+	}
+}
+
+fn test_match_generic_type_in_generic_fn_without_preinstantiation() {
+	base := Named(GenericValue[int]{})
+	assert !is_match[string](base)
+}
-- 
2.39.5