From fc8ef0e70cdb75713db4cc149df78cc1fb5e95fe Mon Sep 17 00:00:00 2001
From: David Legrand <me@davlgd.com>
Date: Thu, 7 May 2026 20:19:12 +0200
Subject: [PATCH] fmt: keep enum name when stringifying fixed-array size
 expressions (#27106)

---
 vlib/v/ast/types.v                            | 34 ++++++++++++++++---
 .../struct_fixed_array_enum_cast_keep.vv      | 16 +++++++++
 2 files changed, 46 insertions(+), 4 deletions(-)
 create mode 100644 vlib/v/fmt/tests/struct_fixed_array_enum_cast_keep.vv

diff --git a/vlib/v/ast/types.v b/vlib/v/ast/types.v
index c3eb64b1d..d6072d4aa 100644
--- a/vlib/v/ast/types.v
+++ b/vlib/v/ast/types.v
@@ -1700,11 +1700,9 @@ pub fn (t &Table) type_to_str_using_aliases(typ Type, import_aliases map[string]
 			elem_str := t.type_to_str_using_aliases(info.elem_type, import_aliases)
 			if info.size_expr is EmptyExpr {
 				res = '[${info.size}]${elem_str}'
-			} else if info.size_expr is Ident {
-				size_str := t.shorten_user_defined_typenames(info.size_expr.name, import_aliases)
-				res = '[${size_str}]${elem_str}'
 			} else {
-				res = '[${info.size_expr}]${elem_str}'
+				size_str := t.fixed_array_size_expr_to_str(info.size_expr, import_aliases)
+				res = '[${size_str}]${elem_str}'
 			}
 		}
 		.chan {
@@ -1858,6 +1856,34 @@ pub fn (t &Table) type_to_str_using_aliases(typ Type, import_aliases map[string]
 	return res
 }
 
+// fixed_array_size_expr_to_str renders a fixed-array size expression preserving
+// fully-qualified enum names. The default `Expr.str()` drops the enum name on
+// `EnumVal` (returning `.value`), which produces invalid output when the size
+// is something like `int(TestEnum._max)` because the enum type cannot be
+// inferred from context inside the array brackets.
+fn (t &Table) fixed_array_size_expr_to_str(expr Expr, import_aliases map[string]string) string {
+	match expr {
+		CastExpr {
+			type_name := t.shorten_user_defined_typenames(t.type_to_str_using_aliases(expr.typ,
+				import_aliases), import_aliases)
+			return '${type_name}(${t.fixed_array_size_expr_to_str(expr.expr, import_aliases)})'
+		}
+		EnumVal {
+			if expr.enum_name != '' {
+				name := t.shorten_user_defined_typenames(expr.enum_name, import_aliases)
+				return '${name}.${expr.val}'
+			}
+			return '.${expr.val}'
+		}
+		Ident {
+			return t.shorten_user_defined_typenames(expr.name, import_aliases)
+		}
+		else {
+			return expr.str()
+		}
+	}
+}
+
 fn (t &Table) shorten_user_defined_typenames(original_name string, import_aliases map[string]string) string {
 	if alias := import_aliases[original_name] {
 		return alias
diff --git a/vlib/v/fmt/tests/struct_fixed_array_enum_cast_keep.vv b/vlib/v/fmt/tests/struct_fixed_array_enum_cast_keep.vv
new file mode 100644
index 000000000..5c645fd41
--- /dev/null
+++ b/vlib/v/fmt/tests/struct_fixed_array_enum_cast_keep.vv
@@ -0,0 +1,16 @@
+module main
+
+enum TestEnum {
+	one
+	two
+	_max
+}
+
+struct Test1 {
+	list [int(TestEnum._max)]int
+}
+
+fn main() {
+	t := Test1{}
+	assert t.list.len == int(TestEnum._max)
+}
-- 
2.39.5