From 30cb3213c0df43f70a43f697996d13fcddc6b0d2 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Thu, 26 Mar 2026 00:12:47 +0300
Subject: [PATCH] cgen: fix interface with method str() returned as option
 (fixes #25931)

---
 vlib/v/gen/c/str_intp.v                       |  3 +-
 ...tion_interface_string_interpolation_test.v | 31 +++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/printing/dump_option_interface_string_interpolation_test.v

diff --git a/vlib/v/gen/c/str_intp.v b/vlib/v/gen/c/str_intp.v
index cc8c872cb..0a8e5ac27 100644
--- a/vlib/v/gen/c/str_intp.v
+++ b/vlib/v/gen/c/str_intp.v
@@ -297,7 +297,8 @@ fn (mut g Gen) str_val(node ast.StringInterLiteral, i int, fmts []u8) {
 			}
 			g.expr(expr)
 		}
-	} else if typ_sym.kind == .interface && (typ_sym.info as ast.Interface).defines_method('str') {
+	} else if !typ.has_option_or_result() && typ_sym.kind == .interface
+		&& (typ_sym.info as ast.Interface).defines_method('str') {
 		rec_type_name := util.no_dots(g.cc_type(typ, false))
 		g.write('${c_name(rec_type_name)}_name_table[')
 		g.expr(expr)
diff --git a/vlib/v/tests/printing/dump_option_interface_string_interpolation_test.v b/vlib/v/tests/printing/dump_option_interface_string_interpolation_test.v
new file mode 100644
index 000000000..7fd35e582
--- /dev/null
+++ b/vlib/v/tests/printing/dump_option_interface_string_interpolation_test.v
@@ -0,0 +1,31 @@
+interface Nested {
+	str() string
+}
+
+struct Leaf {
+	name string
+}
+
+fn (l Leaf) str() string {
+	return l.name
+}
+
+fn denest_none() ?Nested {
+	return none
+}
+
+fn denest_value() ?Nested {
+	return Leaf{'leaf'}
+}
+
+fn test_dump_string_interpolation_of_option_interface_none() {
+	n := denest_none()
+	s := dump('${n}')
+	assert s == 'Option(none)'
+}
+
+fn test_dump_string_interpolation_of_option_interface_value() {
+	n := denest_value()
+	s := dump('${n}')
+	assert s == 'Option(Nested(leaf))'
+}
-- 
2.39.5