From 2bedb097f2f5d8e5489e5c4b2033e9a50a26cc2f Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 11 Mar 2026 11:32:38 +0300
Subject: [PATCH] parser: generic interface methods expect old syntax (fixes
 #25087)

---
 vlib/v/parser/fn.v                            | 21 ++++++++++++++-----
 .../generics/generics_interface_method_test.v |  2 +-
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/vlib/v/parser/fn.v b/vlib/v/parser/fn.v
index 7e6817443..42e10a6f4 100644
--- a/vlib/v/parser/fn.v
+++ b/vlib/v/parser/fn.v
@@ -744,11 +744,22 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 	// generic names can be infer with receiver's generic names
 	if is_method && rec.typ.has_flag(.generic) {
 		sym := p.table.sym(rec.typ)
-		if sym.info is ast.Struct {
-			decl_generic_names := p.types_to_names(sym.info.generic_types, p.tok.pos(),
-				'sym.info.generic_types') or { return ast.FnDecl{
-				scope: unsafe { nil }
-			} }
+		mut rec_generic_types := []ast.Type{}
+		match sym.info {
+			ast.Struct {
+				rec_generic_types = sym.info.generic_types.clone()
+			}
+			ast.Interface {
+				rec_generic_types = sym.info.generic_types.clone()
+			}
+			else {}
+		}
+		if rec_generic_types.len > 0 {
+			decl_generic_names := p.types_to_names(rec_generic_types, p.tok.pos(), 'rec_generic_types') or {
+				return ast.FnDecl{
+					scope: unsafe { nil }
+				}
+			}
 			fn_generic_names := generic_names.clone()
 			generic_names = p.table.generic_type_names(rec.typ)
 			if decl_generic_names.len != generic_names.len {
diff --git a/vlib/v/tests/generics/generics_interface_method_test.v b/vlib/v/tests/generics/generics_interface_method_test.v
index 34454f21a..3d4721234 100644
--- a/vlib/v/tests/generics/generics_interface_method_test.v
+++ b/vlib/v/tests/generics/generics_interface_method_test.v
@@ -3,7 +3,7 @@ mut:
 	next() ?T
 }
 
-fn (mut it Iter[T]) collect[T]() []T {
+fn (mut it Iter[T]) collect() []T {
 	mut data := []T{}
 	for {
 		val := it.next() or { break }
-- 
2.39.5