From 8743be7de9b5181f1d3f844a1a6b600fabd9344e Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Thu, 26 Feb 2026 11:33:13 +0300
Subject: [PATCH] checker: fix implementing a generic interface using a
 concrete type does not compile (fixes #24060)

---
 vlib/v/checker/checker.v                      |  3 +-
 ..._interface_implements_concrete_type_test.v | 38 +++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/generics/generic_interface_implements_concrete_type_test.v

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index bfe6712a2..2793171e8 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1345,7 +1345,8 @@ fn (mut c Checker) type_implements(typ ast.Type, interface_type ast.Type, pos to
 	if mut inter_sym.info is ast.Interface {
 		mut generic_type := interface_type
 		mut generic_info := inter_sym.info
-		if inter_sym.info.parent_type.has_flag(.generic) {
+		if inter_sym.info.parent_type.has_flag(.generic) && (inter_sym.info.concrete_types.len == 0
+			|| inter_sym.info.concrete_types.any(it.has_flag(.generic))) {
 			parent_sym := c.table.sym(inter_sym.info.parent_type)
 			if parent_sym.info is ast.Interface {
 				generic_type = inter_sym.info.parent_type
diff --git a/vlib/v/tests/generics/generic_interface_implements_concrete_type_test.v b/vlib/v/tests/generics/generic_interface_implements_concrete_type_test.v
new file mode 100644
index 000000000..29b9b6cde
--- /dev/null
+++ b/vlib/v/tests/generics/generic_interface_implements_concrete_type_test.v
@@ -0,0 +1,38 @@
+// Regression test for #24060.
+// Explicit `implements Interface[Concrete]` should not force generic inference.
+
+struct System[T] {
+mut:
+	data T
+}
+
+interface Transaction[T] {
+mut:
+	run(mut system System[T])
+}
+
+struct Data {
+mut:
+	dummy string
+}
+
+struct CreateDocumentTransaction implements Transaction[Data] {}
+
+fn (mut txn CreateDocumentTransaction) run(mut system System[Data]) {
+	system.data.dummy = 'updated'
+}
+
+fn apply_transaction(mut system System[Data], mut transaction Transaction[Data]) {
+	transaction.run(mut system)
+}
+
+fn test_generic_interface_implemented_with_concrete_type() {
+	mut system := System[Data]{
+		data: Data{
+			dummy: 'initial'
+		}
+	}
+	mut transaction := CreateDocumentTransaction{}
+	apply_transaction(mut system, mut transaction)
+	assert system.data.dummy == 'updated'
+}
-- 
2.39.5