From 2f54c487608191fac1aacaa8577128771e31f9b0 Mon Sep 17 00:00:00 2001
From: CreeperFace <165158232+dy-tea@users.noreply.github.com>
Date: Fri, 24 Oct 2025 20:49:38 +0100
Subject: [PATCH] checker: ensure ?Struct is not parsed as ??Struct when param
 is ?T (fix #25559) (#25564)

---
 vlib/v/checker/check_types.v                  | 11 +++++-
 .../option_unwrap_unwrap_or_generic_fn_test.v | 37 +++++++++++++++++++
 2 files changed, 47 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/options/option_unwrap_unwrap_or_generic_fn_test.v

diff --git a/vlib/v/checker/check_types.v b/vlib/v/checker/check_types.v
index 31a8f349e..b11814728 100644
--- a/vlib/v/checker/check_types.v
+++ b/vlib/v/checker/check_types.v
@@ -1030,7 +1030,16 @@ fn (mut c Checker) infer_fn_generic_types(func &ast.Fn, mut node ast.CallExpr) {
 			arg := node.args[arg_i]
 			param_sym := c.table.sym(param.typ)
 
-			if param.typ.has_flag(.generic) && param_sym.name == gt_name {
+			if (param.typ.has_flag(.option) && arg.typ.has_flag(.option))
+				|| (param.typ.has_flag(.result) && arg.typ.has_flag(.result)) {
+				param_inner := param.typ.clear_option_and_result()
+				if param_inner.has_flag(.generic) && c.table.sym(param_inner).name == gt_name {
+					typ = arg.typ.clear_option_and_result()
+					if param_inner.nr_muls() > 0 && typ.nr_muls() > 0 {
+						typ = typ.set_nr_muls(0)
+					}
+				}
+			} else if param.typ.has_flag(.generic) && param_sym.name == gt_name {
 				typ = ast.mktyp(arg.typ)
 				if typ == ast.nil_type {
 					typ = ast.voidptr_type
diff --git a/vlib/v/tests/options/option_unwrap_unwrap_or_generic_fn_test.v b/vlib/v/tests/options/option_unwrap_unwrap_or_generic_fn_test.v
new file mode 100644
index 000000000..acb1d6dba
--- /dev/null
+++ b/vlib/v/tests/options/option_unwrap_unwrap_or_generic_fn_test.v
@@ -0,0 +1,37 @@
+fn unwrap[T](t ?T) T {
+	return t or { panic('none') }
+}
+
+fn unwrap_or[T](t ?T, t_or T) T {
+	return t or { t_or }
+}
+
+struct S1 {
+	value int
+}
+
+struct S2 {}
+
+fn test_unwrap() {
+	s1 := ?S1{
+		value: 42
+	}
+	assert unwrap(s1).value == 42
+
+	// see #25566
+	s2 := ?S2(S2{})
+	assert unwrap(s2) == S2{}
+}
+
+fn test_unwrap_or() {
+	s1 := ?S1{
+		value: 42
+	}
+	assert unwrap_or(s1, S1{ value: 12 }).value == 42
+
+	s1n := ?S1(none)
+	assert unwrap_or(s1n, S1{ value: 12 }).value == 12
+
+	s2 := ?S2{}
+	assert unwrap_or(s2, S2{}) == S2{}
+}
-- 
2.39.5