fix corner case in merge_vars (#4289)

fixes #4288

lib/ast.js

@@ -509,10 +509,8 @@ var AST_Lambda = DEFNODE("Lambda", "name argnames length_read uses_arguments", {
     },
     each_argname: function(visit) {
         var tw = new TreeWalker(function(node) {
-            if (node instanceof AST_DestructuredObject) {
+            if (node instanceof AST_DestructuredKeyVal) {
-                node.properties.forEach(function(prop) {
+                node.value.walk(tw);
-                    prop.value.walk(tw);
-                });
                 return true;
             }
             if (node instanceof AST_SymbolFunarg) visit(node);

lib/compress.js

@@ -4739,13 +4739,25 @@ merge(Compressor.prototype, {
                 if (node === self) root = segment;
                 if (node instanceof AST_Lambda) {
                     if (node.name) references[node.name.definition().id] = false;
-                    node.each_argname(node.uses_arguments && !tw.has_directive("use strict") ? function(node) {
+                    var marker = node.uses_arguments && !tw.has_directive("use strict") ? function(node) {
-                        references[node.definition().id] = false;
+                        if (node instanceof AST_SymbolFunarg) references[node.definition().id] = false;
                     } : function(node) {
-                        mark(node, false, true);
+                        if (node instanceof AST_SymbolFunarg) mark(node, false, true);
+                    };
+                    var scanner = new TreeWalker(function(ref) {
+                        if (!(ref instanceof AST_SymbolRef)) return;
+                        var def = ref.definition();
+                        var ldef = node.variables.get(ref.name);
+                        if (ldef && (ldef === def || def.undeclared || node.parent_scope.find_variable(ref) === def)) {
+                            references[ldef.id] = false;
+                        }
+                        return true;
+                    });
+                    node.argnames.forEach(function(argname) {
+                        argname.mark_symbol(marker, scanner);
                     });
                 }
-                descend();
+                walk_body(node, tw);
                 pop();
                 return true;
             }

test/compress/destructured.js

@@ -1440,3 +1440,33 @@ issue_4286_2: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_4288: {
+    options = {
+        merge_vars: true,
+    }
+    input: {
+        function f({
+            [new function() {
+                console.log(typeof b);
+            }()]: a,
+        }) {
+            var b = a;
+            b++;
+        }
+        f(0);
+    }
+    expect: {
+        function f({
+            [new function() {
+                console.log(typeof b);
+            }()]: a,
+        }) {
+            var b = a;
+            b++;
+        }
+        f(0);
+    }
+    expect_stdout: "undefined"
+    node_version: ">=6"
+}