[acorn-opt] Use walkPattern for variable declarators too (#24553)

Author: RReverser

test/js_optimizer/JSDCE-objectPattern-output.js

@@ -5,7 +5,6 @@ let z = 50;
 globalThis.f = function([, r]) {
   let {a, b} = r;
   let {z: c} = r;
-  let [, i, {foo: p, bar: q}] = r;
   return g(a, b, c, d, z);
 };
 

tools/acorn-optimizer.mjs

@@ -243,17 +243,16 @@ function JSDCE(ast, aggressive) {
           let removedHere = 0;
           node.declarations = node.declarations.filter((node) => {
             assert(node.type === 'VariableDeclarator');
-            const id = node.id;
-            if (id.type === 'ObjectPattern' || id.type === 'ArrayPattern') {
-              // TODO: DCE into object patterns, that is, things like
-              //         let { a, b } = ..
-              //         let [ a, b ] = ..
-              return true;
-            }
-            assert(id.type === 'Identifier');
-            const curr = id.name;
-            const value = node.init;
-            const keep = !names.has(curr) || (value && hasSideEffects(value));
+            let keep = node.init && hasSideEffects(node.init);
+            walkPattern(
+              node.id,
+              (value) => {
+                keep ||= hasSideEffects(value);
+              },
+              (boundName) => {
+                keep ||= !names.has(boundName);
+              },
+            );
             if (!keep) removedHere = 1;
             return keep;
           });