From 267475d919454faf39dc54db1f7b802fe86698fa Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Fri, 24 Apr 2026 01:19:21 +0300
Subject: [PATCH] checker: fix Regression: V can't match generics variant
 (fixes #26866)

---
 vlib/v/checker/match.v                        | 14 ++++---
 .../tests/generics/generic_match_expr_test.v  | 38 +++++++++++++++++++
 2 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/vlib/v/checker/match.v b/vlib/v/checker/match.v
index 32abe707a..2c100d4ff 100644
--- a/vlib/v/checker/match.v
+++ b/vlib/v/checker/match.v
@@ -703,6 +703,7 @@ fn (mut c Checker) match_exprs(mut node ast.MatchExpr, cond_type_sym ast.TypeSym
 		mut expr_types := []ast.TypeNode{}
 		for k, mut expr in branch.exprs {
 			mut key := ''
+			mut resolved_type_node := ast.no_type
 			// TODO: investigate why enums are different here:
 			if expr !is ast.EnumVal && !(node.is_comptime && expr is ast.ComptimeType) {
 				// ensure that the sub expressions of the branch are actually checked, before anything else:
@@ -787,12 +788,11 @@ fn (mut c Checker) match_exprs(mut node ast.MatchExpr, cond_type_sym ast.TypeSym
 			is_type_node := expr is ast.TypeNode || expr is ast.ComptimeType
 			match mut expr {
 				ast.TypeNode {
-					expr_typ := c.recheck_concrete_type(expr.typ)
-					key = c.table.type_to_str(expr_typ)
-					expr.typ = expr_typ
+					resolved_type_node = c.recheck_concrete_type(expr.typ)
+					key = c.table.type_to_str(resolved_type_node)
 					expr_types << ast.TypeNode{
 						...expr
-						typ: expr_typ
+						typ: resolved_type_node
 					}
 				}
 				ast.EnumVal {
@@ -875,7 +875,11 @@ fn (mut c Checker) match_exprs(mut node ast.MatchExpr, cond_type_sym ast.TypeSym
 					}
 				}
 			} else {
-				expr_type := c.expr(mut expr)
+				expr_type := if expr is ast.TypeNode {
+					resolved_type_node
+				} else {
+					c.expr(mut expr)
+				}
 				if expr_type.idx() == 0 {
 					// parser failed, stop checking
 					return
diff --git a/vlib/v/tests/generics/generic_match_expr_test.v b/vlib/v/tests/generics/generic_match_expr_test.v
index a6188b2c2..303404489 100644
--- a/vlib/v/tests/generics/generic_match_expr_test.v
+++ b/vlib/v/tests/generics/generic_match_expr_test.v
@@ -22,3 +22,41 @@ fn test_main() {
 	t('')!
 	assert true
 }
+
+type GenericMatchSumtype[T] = GenericMatchY[T] | GenericMatchZ[T]
+
+fn (mut x GenericMatchSumtype[T]) do_it[T]() string {
+	match mut x {
+		GenericMatchY[T] { return 'doing GenericMatchY' }
+		GenericMatchZ[T] { return 'doing GenericMatchZ' }
+	}
+
+	return ''
+}
+
+struct GenericMatchY[T] {
+	name  string
+	value T
+}
+
+struct GenericMatchZ[T] {
+	name  string
+	value T
+}
+
+fn test_match_generic_sumtype_variant_in_generic_method() {
+	y := GenericMatchY[int]{
+		name:  'Y'
+		value: 1
+	}
+	z := GenericMatchZ[bool]{
+		name:  'Z'
+		value: true
+	}
+
+	mut x1 := GenericMatchSumtype[int](y)
+	assert x1.do_it() == 'doing GenericMatchY'
+
+	mut x2 := GenericMatchSumtype[bool](z)
+	assert x2.do_it() == 'doing GenericMatchZ'
+}
-- 
2.39.5