Fix support for JS destructuring in acorn optimizer pass (#20635)

Fixes: #20631

Author: sbc100

test/optimizer/JSDCE-defaultArg-output.js

@@ -1,7 +1,9 @@
 var usedAsDefaultArg = 42;
 
-function g(a, b = usedAsDefaultArg) {
- return a + b + 1;
+var usedAsDefaultArg2 = [ 1, 2 ];
+
+function g({notUsed: notUsed}, a, b = usedAsDefaultArg, [c, d] = usedAsDefaultArg2) {
+ return a + b + notUsed + 1;
 }
 
 Module["g"] = g;

test/optimizer/JSDCE-defaultArg.js

@@ -1,9 +1,10 @@
 var usedAsDefaultArg = 42;
+var usedAsDefaultArg2 = [1,2];
 var notUsed = 43;
 
 // exported
-function g(a, b = usedAsDefaultArg) {
-  return a+b+1;
+function g({notUsed}, a, b = usedAsDefaultArg, [c, d] = usedAsDefaultArg2) {
+  return a+b+notUsed+1;
 }
 
 Module['g'] = g;

tools/acorn-optimizer.js

@@ -371,18 +371,28 @@ function runJSDCE(ast, aggressive) {
       }
       const scope = {};
       scopes.push(scope);
-      node.params.forEach((param) => {
+      node.params.forEach(function traverse(param) {
         if (param.type === 'RestElement') {
           param = param.argument;
         }
         if (param.type === 'AssignmentPattern') {
           c(param.right);
           param = param.left;
         }
-        assert(param.type === 'Identifier', param.type);
-        const name = param.name;
-        ensureData(scope, name).def = 1;
-        scope[name].param = 1;
+        if (param.type === 'ArrayPattern') {
+          for (var elem of param.elements) {
+            traverse(elem);
+          }
+        } else if (param.type === 'ObjectPattern') {
+          for (var prop of param.properties) {
+            traverse(prop.key);
+          }
+        } else {
+          assert(param.type === 'Identifier', param.type);
+          const name = param.name;
+          ensureData(scope, name).def = 1;
+          scope[name].param = 1;
+        }
       });
       c(node.body);
       // we can ignore self-references, i.e., references to ourselves inside