From 933e0984396b1f940cdb6b2791448f5792e25735 Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc@chromium.org>
Date: Tue, 5 Dec 2023 10:12:31 -0800
Subject: [PATCH] Fix js-optimizer crash on empty array destructuring element

Followup to #20835.

Fixes: #20818
---
 test/optimizer/JSDCE-objectPattern-output.js | 2 +-
 test/optimizer/JSDCE-objectPattern.js        | 2 +-
 tools/acorn-optimizer.js                     | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/test/optimizer/JSDCE-objectPattern-output.js b/test/optimizer/JSDCE-objectPattern-output.js
index 42e4892c4ce80..7aa8f6136f2fb 100644
--- a/test/optimizer/JSDCE-objectPattern-output.js
+++ b/test/optimizer/JSDCE-objectPattern-output.js
@@ -5,7 +5,7 @@ let z = 50;
 globalThis.f = function(r) {
  let {a: a, b: b} = r;
  let {z: c} = r;
- let [i, {foo: p, bar: q}] = r;
+ let [, i, {foo: p, bar: q}] = r;
  return g(a, b, c, d, z);
 };
 
diff --git a/test/optimizer/JSDCE-objectPattern.js b/test/optimizer/JSDCE-objectPattern.js
index 3b7899f4cc419..934791538ab69 100644
--- a/test/optimizer/JSDCE-objectPattern.js
+++ b/test/optimizer/JSDCE-objectPattern.js
@@ -13,7 +13,7 @@ let z = 50;
 globalThis.f = function(r) {
   let { a, b } = r;
   let { z: c } = r;
-  let [i, {foo : p, bar : q}] = r;
+  let [/*empty*/, i, {foo : p, bar : q}] = r;
   return g(a, b, c, d, z);
 };
 
diff --git a/tools/acorn-optimizer.js b/tools/acorn-optimizer.js
index 7429fbef412d1..4edaec54ba5ec 100755
--- a/tools/acorn-optimizer.js
+++ b/tools/acorn-optimizer.js
@@ -433,7 +433,7 @@ function runJSDCE(ast, aggressive) {
             }
           } else if (id.type === 'ArrayPattern') {
             for (const elem of id.elements) {
-              traverse(elem);
+              if (elem) traverse(elem);
             }
           } else {
             assertAt(id.type === 'Identifier', id, `expected Indentifier but found ${id.type}`);