private accounting for collapse_vars

- avoid issues with identity reference due to deep cloning

fixes #2437

lib/compress.js

@@ -788,6 +788,14 @@ merge(Compressor.prototype, {
             || compressor.option("unsafe") && global_names(this.name);
     });
 
+    function drop_decl(def) {
+        def._eliminiated = (def._eliminiated || 0) + 1;
+        if (def.orig.length == def._eliminiated) {
+            def.scope.functions.del(def.name);
+            def.scope.variables.del(def.name);
+        }
+    }
+
     function tighten_body(statements, compressor) {
         var CHANGED, max_iter = 10;
         do {
@@ -1000,7 +1008,8 @@ merge(Compressor.prototype, {
             function get_lhs(expr) {
                 if (expr instanceof AST_VarDef) {
                     var def = expr.name.definition();
-                    if (def.orig.length > 1 && !(expr.name instanceof AST_SymbolFunarg)
+                    if (def.orig.length - (def._eliminiated || 0) > 1
+                            && !(expr.name instanceof AST_SymbolFunarg)
                         || def.references.length == 1 && !compressor.exposed(def)) {
                         return make_node(AST_SymbolRef, expr.name, expr.name);
                     }
@@ -1047,7 +1056,7 @@ merge(Compressor.prototype, {
                     if (node === expr) {
                         found = true;
                         if (node instanceof AST_VarDef) {
-                            remove(node.name.definition().orig, node.name);
+                            drop_decl(node.name.definition());
                             node.value = null;
                             return node;
                         }
@@ -2420,7 +2429,7 @@ merge(Compressor.prototype, {
                     var def = node.name.definition();
                     if (!(def.id in in_use_ids)) {
                         compressor[node.name.unreferenced() ? "warn" : "info"]("Dropping unused function {name} [{file}:{line},{col}]", template(node.name));
-                        drop_decl(def, node.name);
+                        drop_decl(def);
                         return make_node(AST_EmptyStatement, node);
                     }
                     return node;
@@ -2442,7 +2451,7 @@ merge(Compressor.prototype, {
                                 if (var_defs.length > 1 && !def.value) {
                                     compressor.warn("Dropping duplicated definition of variable {name} [{file}:{line},{col}]", template(def.name));
                                     remove(var_defs, def);
-                                    drop_decl(sym, def.name);
+                                    drop_decl(sym);
                                     return;
                                 }
                             }
@@ -2475,7 +2484,7 @@ merge(Compressor.prototype, {
                             } else {
                                 compressor[def.name.unreferenced() ? "warn" : "info"]("Dropping unused variable {name} [{file}:{line},{col}]", template(def.name));
                             }
-                            drop_decl(sym, def.name);
+                            drop_decl(sym);
                         }
                     });
                     if (head.length == 0 && tail.length == 1 && tail[0].name instanceof AST_SymbolVar) {
@@ -2484,7 +2493,7 @@ merge(Compressor.prototype, {
                             var def = tail.pop();
                             compressor.warn("Converting duplicated definition of variable {name} to assignment [{file}:{line},{col}]", template(def.name));
                             remove(var_defs, def);
-                            drop_decl(def.name.definition(), def.name);
+                            drop_decl(def.name.definition());
                             side_effects.unshift(make_node(AST_Assign, def, {
                                 operator: "=",
                                 left: make_node(AST_SymbolRef, def.name, def.name),
@@ -2566,14 +2575,6 @@ merge(Compressor.prototype, {
                         col  : sym.start.col
                     };
                 }
-
-                function drop_decl(def, decl) {
-                    remove(def.orig, decl);
-                    if (!def.orig.length) {
-                        def.scope.functions.del(def.name);
-                        def.scope.variables.del(def.name);
-                    }
-                }
             }
         );
         self.transform(tt);
@@ -3293,7 +3294,7 @@ merge(Compressor.prototype, {
                 }));
                 if (reduce_vars) name.definition().fixed = false;
             }
-            remove(def.name.definition().orig, def.name);
+            drop_decl(def.name.definition());
             return a;
         }, []);
         if (assignments.length == 0) return null;

test/compress/collapse_vars.js

@@ -3029,3 +3029,51 @@ issue_2425_3: {
     }
     expect_stdout: "15"
 }
+
+issue_2437: {
+    options = {
+        collapse_vars: true,
+        conditionals: true,
+        inline: true,
+        join_vars: true,
+        reduce_vars: true,
+        side_effects: true,
+        sequences: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        function foo() {
+            bar();
+        }
+        function bar() {
+            if (xhrDesc) {
+                var req = new XMLHttpRequest();
+                var result = !!req.onreadystatechange;
+                Object.defineProperty(XMLHttpRequest.prototype, 'onreadystatechange', xhrDesc || {});
+                return result;
+            }
+            else {
+                var req = new XMLHttpRequest();
+                var detectFunc = function () { };
+                req.onreadystatechange = detectFunc;
+                var result = req[SYMBOL_FAKE_ONREADYSTATECHANGE_1] === detectFunc;
+                req.onreadystatechange = null;
+                return result;
+            }
+        }
+        foo();
+    }
+    expect: {
+        !function() {
+            if (xhrDesc)
+                return result = !!(req = new XMLHttpRequest()).onreadystatechange,
+                    Object.defineProperty(XMLHttpRequest.prototype, "onreadystatechange", xhrDesc || {}),
+                    result;
+            var req = new XMLHttpRequest(), detectFunc = function() {};
+            req.onreadystatechange = detectFunc;
+            var result = req[SYMBOL_FAKE_ONREADYSTATECHANGE_1] === detectFunc;
+            req.onreadystatechange = null;
+        }();
+    }
+}