From dd75c4b233f91e974c1fa1c3f6e023a9670688e8 Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Sun, 29 Dec 2024 17:55:58 -0300
Subject: [PATCH 1/2] fix

---
 vlib/v/checker/infix.v                        |  2 +-
 .../sumtypes/sumtype_generic_checking_test.v  | 20 +++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/sumtypes/sumtype_generic_checking_test.v

diff --git a/vlib/v/checker/infix.v b/vlib/v/checker/infix.v
index 47206adabed330..a1c8388285116d 100644
--- a/vlib/v/checker/infix.v
+++ b/vlib/v/checker/infix.v
@@ -756,7 +756,7 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 			right_expr := node.right
 			mut typ := match right_expr {
 				ast.TypeNode {
-					right_expr.typ
+					c.unwrap_generic(right_expr.typ)
 				}
 				ast.None {
 					ast.none_type_idx
diff --git a/vlib/v/tests/sumtypes/sumtype_generic_checking_test.v b/vlib/v/tests/sumtypes/sumtype_generic_checking_test.v
new file mode 100644
index 00000000000000..66e1f6734cb721
--- /dev/null
+++ b/vlib/v/tests/sumtypes/sumtype_generic_checking_test.v
@@ -0,0 +1,20 @@
+type Sumtype = string | int
+
+fn generic_fn[T]() ?T {
+	a := Sumtype('123')
+	if a is T {
+		return a
+	}
+
+	b := Sumtype(123)
+	if b is T {
+		return b
+	}
+
+	return none
+}
+
+fn test_main() {
+	assert generic_fn[string]().str() == "Option('123')"
+	assert generic_fn[int]().str() == 'Option(123)'
+}

From b3d3b490cff0e834b477e9636e5804396fa8bc5f Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Sun, 29 Dec 2024 18:44:14 -0300
Subject: [PATCH 2/2] fix

---
 vlib/v/checker/infix.v | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/vlib/v/checker/infix.v b/vlib/v/checker/infix.v
index a1c8388285116d..66e6d212adf694 100644
--- a/vlib/v/checker/infix.v
+++ b/vlib/v/checker/infix.v
@@ -756,7 +756,7 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 			right_expr := node.right
 			mut typ := match right_expr {
 				ast.TypeNode {
-					c.unwrap_generic(right_expr.typ)
+					right_expr.typ
 				}
 				ast.None {
 					ast.none_type_idx
@@ -794,7 +794,8 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 					c.error('`${op}` can only be used with interfaces and sum types',
 						node.pos) // can be used in sql too, but keep err simple
 				} else if mut left_sym.info is ast.SumType {
-					if typ !in left_sym.info.variants {
+					if typ !in left_sym.info.variants
+						&& c.unwrap_generic(typ) !in left_sym.info.variants {
 						c.error('`${left_sym.name}` has no variant `${right_sym.name}`',
 							right_pos)
 					}