Provide placeholders for proper function length.

lib/6to5/transformation/transformers/es6/tail-call.js

@@ -210,6 +210,4 @@ exports.FunctionExpression = function (node, parent, scope) {
     ]), shouldContinueId),
     t.returnStatement(resultId)
   ]);
-
-  node.params = [];
 };

lib/6to5/transformation/transformers/index.js

@@ -52,13 +52,13 @@ module.exports = {
   // needs to be after `es6.blockScoping` due to needing `letReferences` set on blocks
   "es6.blockScopingTDZ":                   require("./es6/block-scoping-tdz"),
 
-  "es6.tailCall":                          require("./es6/tail-call"),
-
   "es6.parameters.default":                require("./es6/parameters.default"),
   "es6.parameters.rest":                   require("./es6/parameters.rest"),
 
   "es6.destructuring":                     require("./es6/destructuring"),
 
+  "es6.tailCall":                          require("./es6/tail-call"),
+
   regenerator:                             require("./other/regenerator"),
 
   // needs to be after `regenerator` due to needing `regeneratorRuntime` references

test/fixtures/transformation/es6-tail-call/call-apply/expected.js

@@ -1,6 +1,6 @@
 "use strict";
 
-(function f() {
+(function f(n) {
   var _arguments = arguments,
       _this = this,
       _shouldContinue,

test/fixtures/transformation/es6-tail-call/expressions/expected.js

@@ -1,6 +1,6 @@
 "use strict";
 
-(function f() {
+(function f(n) {
   var _arguments = arguments,
       _this = this,
       _shouldContinue,

test/fixtures/transformation/es6-tail-call/recursion/actual.js

@@ -1,4 +1,4 @@
-(function f(n, /* should be undefined after first pass */ m) {
+(function f(n = getDefaultValue(), /* should be undefined after first pass */ m) {
   if (n <= 0) {
     return "foo";
   }

test/fixtures/transformation/es6-tail-call/recursion/exec.js

@@ -0,0 +1,9 @@
+var timeLimit = Date.now() + 1000;
+
+assert.equal((function f(n) {
+  assert.operator(Date.now(), '<', timeLimit, "Timeout");
+  if (n <= 0) {
+    return "foo";
+  }
+  return f(n - 1);
+})(1e6), "foo");

test/fixtures/transformation/es6-tail-call/recursion/expected.js

@@ -1,13 +1,14 @@
 "use strict";
 
-(function f() {
+(function f(_x, /* should be undefined after first pass */m) {
   var _arguments = arguments,
       _this = this,
       _shouldContinue,
       _result;
   do {
     _shouldContinue = false;
-    _result = (function (n, /* should be undefined after first pass */m) {
+    _result = (function (_x, m) {
+      var n = arguments[0] === undefined ? getDefaultValue() : arguments[0];
       if (n <= 0) {
         return "foo";
       }

test/fixtures/transformation/es6-tail-call/try-catch/expected.js

@@ -9,7 +9,7 @@
   } catch (e) {}
 })(1000000) === "foo";
 
-(function f() {
+(function f(n) {
   var _arguments = arguments,
       _this = this,
       _shouldContinue,
@@ -43,7 +43,7 @@
   } finally {}
 })(1000000) === "foo";
 
-(function f() {
+(function f(n) {
   var _arguments = arguments,
       _this = this,
       _shouldContinue,