From e8f2a54a672c65828f5fe683b467a00a4a8a097a Mon Sep 17 00:00:00 2001
From: pjh456 <147148383@qq.com>
Date: Sat, 19 Sep 2026 15:41:22 +0000
Subject: [PATCH] =?UTF-8?q?fix:=20concat=20=E7=A9=BA=E6=95=B0=E7=BB=84?=
 =?UTF-8?q?=E5=AE=9E=E5=8F=82=E6=8C=89=20ConcatSteps=20=E5=B1=95=E5=BC=80?=
 =?UTF-8?q?=E4=B8=BA=E9=9B=B6=E5=85=83=E7=B4=A0?=
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---
 crates/oxide_builtins/src/array/element.rs    |  4 +--
 .../tests/array_hole_semantics_tests.rs       | 25 +++++++++++++++++++
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/crates/oxide_builtins/src/array/element.rs b/crates/oxide_builtins/src/array/element.rs
index f777b263..9517b15c 100644
--- a/crates/oxide_builtins/src/array/element.rs
+++ b/crates/oxide_builtins/src/array/element.rs
@@ -412,8 +412,8 @@ pub fn array_concat<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
             if !o_ptr.is_null() {
                 let o = unsafe { &*o_ptr };
                 let on = o.prop_count() as usize;
-                // 真数组时展开元素（洞位同样留洞）。
-                if o.is_array() && on > 0 {
+                // 真数组时展开元素（空数组展开为零元素，贡献无；洞位同样留洞）。
+                if o.is_array() {
                     let dense = o.array_elements_meta_vec().is_none();
                     for i in 0..on {
                         if dense || !o.prop_meta_at(i).is_some_and(|m| m.is_hole()) {
diff --git a/crates/oxide_builtins/tests/array_hole_semantics_tests.rs b/crates/oxide_builtins/tests/array_hole_semantics_tests.rs
index 67e44e9a..2dbd1027 100644
--- a/crates/oxide_builtins/tests/array_hole_semantics_tests.rs
+++ b/crates/oxide_builtins/tests/array_hole_semantics_tests.rs
@@ -526,3 +526,28 @@ fn test_splice_reverse_primitive_this_boxed() {
     .unwrap();
     assert_eq!(out, "true|true|0");
 }
+
+// 引擎钉：concat 空数组实参按 ConcatSteps 展开为零元素——不贡献元素也不占位。
+#[test]
+fn test_concat_empty_array_arg_expands_zero_elements() {
+    let out = eval_str(
+        "(() => { return [1].concat([]).length + '|' + [1].concat([], []).length + '|' + \
+         [].concat([]).length + '|' + [1, 2].concat(new Array(0)).length; })()",
+    )
+    .unwrap();
+    assert_eq!(out, "1|1|0|2");
+}
+
+// 引擎钉：concat 多实参混合 present/空数组/非数组实参展开序与规范一致，
+// 空数组实参中间穿插不占位；洞实参位保洞。
+#[test]
+fn test_concat_mixed_args_order_and_holes() {
+    let out = eval_str(
+        "(() => { const mixed = [].concat([], 5, []).join(','); \
+         const ordered = [1].concat([2, 3], 0, []).join(','); \
+         const r = [].concat(new Array(1)); \
+         return mixed + '|' + ordered + '|' + r.length + '|' + (0 in r); })()",
+    )
+    .unwrap();
+    assert_eq!(out, "5|1,2,3,0|1|false");
+}