From 98c89bb0f6d5182d7bb2d3a686286a4a489c89b7 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 27 May 2026 14:22:42 +0300
Subject: [PATCH] gen/c: add coutput regression test for empty .attrs inline
 init (#27274)

`.c.must_have` for the 3 distinct inline initializers + a coutput_test
function asserting no `__new_array_with_default(0, 0, sizeof(...), 0)`
sneaks back in for `$for field/method/val` with empty attrs.
---
 vlib/v/gen/c/coutput_test.v                   | 12 +++++++
 ...me_for_empty_attrs_inline_init.c.must_have |  3 ++
 .../comptime_for_empty_attrs_inline_init.vv   | 36 +++++++++++++++++++
 3 files changed, 51 insertions(+)
 create mode 100644 vlib/v/gen/c/testdata/comptime_for_empty_attrs_inline_init.c.must_have
 create mode 100644 vlib/v/gen/c/testdata/comptime_for_empty_attrs_inline_init.vv

diff --git a/vlib/v/gen/c/coutput_test.v b/vlib/v/gen/c/coutput_test.v
index 57219918b..edf8f5822 100644
--- a/vlib/v/gen/c/coutput_test.v
+++ b/vlib/v/gen/c/coutput_test.v
@@ -247,6 +247,18 @@ fn test_imported_empty_interface_concat_does_not_emit_noop_array_cast_helper() {
 	assert !compilation.output.contains(symbol)
 }
 
+fn test_comptime_for_empty_attrs_does_not_emit_new_array_calls() {
+	os.chdir(vroot) or {}
+	path := os.join_path(testdata_folder, 'comptime_for_empty_attrs_inline_init.vv')
+	cmd := '${os.quoted_path(vexe)} -o - ${os.quoted_path(path)}'
+	compilation := os.execute(cmd)
+	ensure_compilation_succeeded(compilation, cmd)
+	// regression for https://github.com/vlang/v/issues/27274
+	assert !compilation.output.contains('builtin____new_array_with_default(0, 0, sizeof(string), 0)')
+	assert !compilation.output.contains('builtin____new_array_with_default(0, 0, sizeof(VAttribute), 0)')
+	assert !compilation.output.contains('builtin____new_array_with_default(0, 0, sizeof(FunctionParam), 0)')
+}
+
 fn test_windows_sharedlive_string_interpolation_in_ternary_does_not_emit_inline_tmp_decl() {
 	os.chdir(vroot) or {}
 	test_source := os.join_path(os.vtmp_dir(), 'coutput_live_windows_ternary_str_intp.vv')
diff --git a/vlib/v/gen/c/testdata/comptime_for_empty_attrs_inline_init.c.must_have b/vlib/v/gen/c/testdata/comptime_for_empty_attrs_inline_init.c.must_have
new file mode 100644
index 000000000..32cbdda0d
--- /dev/null
+++ b/vlib/v/gen/c/testdata/comptime_for_empty_attrs_inline_init.c.must_have
@@ -0,0 +1,3 @@
+.attrs = ((array){.data = 0, .offset = 0, .len = 0, .cap = 0, .flags = 0, .element_size = sizeof(string)});
+.attributes = ((array){.data = 0, .offset = 0, .len = 0, .cap = 0, .flags = 0, .element_size = sizeof(VAttribute)});
+.args = ((array){.data = 0, .offset = 0, .len = 0, .cap = 0, .flags = 0, .element_size = sizeof(FunctionParam)});
diff --git a/vlib/v/gen/c/testdata/comptime_for_empty_attrs_inline_init.vv b/vlib/v/gen/c/testdata/comptime_for_empty_attrs_inline_init.vv
new file mode 100644
index 000000000..c870557cc
--- /dev/null
+++ b/vlib/v/gen/c/testdata/comptime_for_empty_attrs_inline_init.vv
@@ -0,0 +1,36 @@
+// Regression for https://github.com/vlang/v/issues/27274 — empty
+// `.attrs`/`.attributes`/`.args` in `$for field/method/val` must
+// be initialised inline (no `__new_array_with_default` call).
+struct Foo {
+	a string
+}
+
+fn (f Foo) m() {}
+
+enum Color {
+	red
+}
+
+fn exercise_fields[T]() {
+	$for field in T.fields {
+		_ := field.name
+	}
+}
+
+fn exercise_methods[T]() {
+	$for method in T.methods {
+		_ := method.name
+	}
+}
+
+fn exercise_values[T]() {
+	$for val in T.values {
+		_ := val.name
+	}
+}
+
+fn main() {
+	exercise_fields[Foo]()
+	exercise_methods[Foo]()
+	exercise_values[Color]()
+}
-- 
2.39.5