fix corner case in merge_vars (#5466)

fixes #5465

lib/compress.js

@@ -6044,31 +6044,7 @@ Compressor.prototype.compress = function(node) {
                 var rhs = node.right;
                 if (lhs instanceof AST_Destructured) {
                     rhs.walk(tw);
-                    var marker = new TreeWalker(function(node) {
-                        if (node instanceof AST_Destructured) return;
-                        if (node instanceof AST_DefaultValue) {
-                            push();
-                            node.value.walk(tw);
-                            pop();
-                            node.name.walk(marker);
-                        } else if (node instanceof AST_DestructuredKeyVal) {
-                            if (node.key instanceof AST_Node) {
-                                push();
-                                segment.block = node;
-                                node.key.walk(tw);
-                                node.value.walk(marker);
-                                pop();
-                            } else {
-                                node.value.walk(marker);
-                            }
-                        } else if (node instanceof AST_SymbolRef) {
-                            mark(node);
-                        } else {
-                            node.walk(tw);
-                        }
-                        return true;
-                    });
-                    lhs.walk(marker);
+                    walk_destructured(AST_SymbolRef, mark, lhs);
                     return true;
                 }
                 if (lazy_op[node.operator.slice(0, -1)]) {
@@ -6196,15 +6172,15 @@ Compressor.prototype.compress = function(node) {
                 if (node instanceof AST_Lambda) {
                     if (node.name) references[node.name.definition().id] = false;
                     var marker = node.uses_arguments && !tw.has_directive("use strict") ? function(node) {
-                        if (node instanceof AST_SymbolFunarg) references[node.definition().id] = false;
+                        references[node.definition().id] = false;
                     } : function(node) {
-                        if (node instanceof AST_SymbolFunarg) mark(node);
+                        mark(node);
                     };
                     in_arg.push(node);
                     node.argnames.forEach(function(argname) {
-                        argname.mark_symbol(marker, tw);
+                        walk_destructured(AST_SymbolFunarg, marker, argname);
                     });
-                    if (node.rest) node.rest.mark_symbol(marker, tw);
+                    if (node.rest) walk_destructured(AST_SymbolFunarg, marker, node.rest);
                     in_arg.pop();
                 }
                 walk_lambda(node, tw);
@@ -6419,6 +6395,34 @@ Compressor.prototype.compress = function(node) {
             segment = Object.getPrototypeOf(segment);
         }
 
+        function walk_destructured(symbol_type, mark, lhs) {
+            var marker = new TreeWalker(function(node) {
+                if (node instanceof AST_Destructured) return;
+                if (node instanceof AST_DefaultValue) {
+                    push();
+                    node.value.walk(tw);
+                    pop();
+                    node.name.walk(marker);
+                } else if (node instanceof AST_DestructuredKeyVal) {
+                    if (node.key instanceof AST_Node) {
+                        push();
+                        segment.block = node;
+                        node.key.walk(tw);
+                        node.value.walk(marker);
+                        pop();
+                    } else {
+                        node.value.walk(marker);
+                    }
+                } else if (node instanceof symbol_type) {
+                    mark(node);
+                } else {
+                    node.walk(tw);
+                }
+                return true;
+            });
+            lhs.walk(marker);
+        }
+
         function mark(sym, read) {
             var def = sym.definition(), ldef;
             if (read && !all(in_arg, function(fn) {

test/compress/default-values.js

@@ -2421,3 +2421,30 @@ issue_5463: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_5465: {
+    options = {
+        inline: true,
+        merge_vars: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        function f(a, b) {
+            (function(c = b = "FAIL 2") {
+                this && console.log(b || "PASS");
+            })(42 - a && a);
+        }
+        f("FAIL 1");
+    }
+    expect: {
+        a = "FAIL 1",
+        void function(c = b = "FAIL 2") {
+            this && console.log(b || "PASS");
+        }(42 - a && a);
+        var a, b;
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}

test/compress/destructured.js

@@ -1815,8 +1815,8 @@ issue_4288: {
                 console.log(typeof b);
             }()]: a,
         }) {
-            var a = a;
-            a++;
+            var b = a;
+            b++;
         }
         f(0);
     }
@@ -1848,8 +1848,8 @@ issue_4294: {
             }) {}({
                 [a]: 0,
             });
-            var a = A;
-            console.log(a);
+            var b = A;
+            console.log(b);
         })();
     }
     expect_stdout: "PASS"