Fix scope of function body when var redeclares param (#11158)

* Fix scope of function body when var redeclares param

* Fix empty var declarations

* Apply suggestions

packages/babel-plugin-transform-parameters/test/fixtures/parameters/fn-decl-same-as-param/input.js

@@ -0,0 +1,5 @@
+function foo(a = 2) {
+  function a() {
+
+  }
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/fn-decl-same-as-param/output.js

@@ -0,0 +1,6 @@
+function foo() {
+  var a = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : 2;
+  return function () {
+    function a() {}
+  }();
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-no-init-same-as-param/input.js

@@ -0,0 +1,6 @@
+function f(a = 2, b = 3) {
+  var a, b = 4;
+  var a;
+  var b;
+  return a + b;
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-no-init-same-as-param/output.js

@@ -0,0 +1,8 @@
+function f() {
+  var a = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : 2;
+  var b = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 3;
+  return function () {
+    var b = 4;
+    return a + b;
+  }();
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-no-init-then-var-with-init-same-as-param/input.js

@@ -0,0 +1,5 @@
+function f(a = 2, b = 3) {
+  var a;
+  var { a } = { a: 4 };
+  return a + b;
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-no-init-then-var-with-init-same-as-param/output.js

@@ -0,0 +1,11 @@
+function f() {
+  var a = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : 2;
+  var b = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 3;
+  return function () {
+    var _a = {
+      a: 4
+    },
+        a = _a.a;
+    return a + b;
+  }();
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-same-as-array-pattern-param/input.js

@@ -0,0 +1,5 @@
+function foo({a, b}) {
+  var a = 3;
+  var c = 2;
+  var d = a + b + c;
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-same-as-array-pattern-param/output.js

@@ -0,0 +1,9 @@
+function foo(_ref) {
+  var a = _ref.a,
+      b = _ref.b;
+  return function () {
+    var a = 3;
+    var c = 2;
+    var d = a + b + c;
+  }();
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-same-as-object-pattern-param/input.js

@@ -0,0 +1,5 @@
+function foo([a, b]) {
+  var a = 3;
+  var c = 2;
+  var d = a + b + c;
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-same-as-object-pattern-param/output.js

@@ -0,0 +1,11 @@
+function foo(_ref) {
+  var _ref2 = babelHelpers.slicedToArray(_ref, 2),
+      a = _ref2[0],
+      b = _ref2[1];
+
+  return function () {
+    var a = 3;
+    var c = 2;
+    var d = a + b + c;
+  }();
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-same-as-param-closure/exec.js

@@ -0,0 +1,8 @@
+var x = 1
+function foo(x, y = function () { x = 2 }) {
+  var x = 3
+  y()
+  expect(x).toBe(3);
+}
+foo()
+expect(x).toBe(1);

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-same-as-param/input.js

@@ -0,0 +1,3 @@
+function foo(a = 2) {
+  var a = 1;
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-same-as-param/output.js

@@ -0,0 +1,6 @@
+function foo() {
+  var a = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : 2;
+  return function () {
+    var a = 1;
+  }();
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-with-init-then-var-no-init-same-as-param/input.js

@@ -0,0 +1,6 @@
+function f(a = 2, b = 3) {
+  var { a } = { a: 4 };
+  var a;
+  var b;
+  return a + b;
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/var-with-init-then-var-no-init-same-as-param/output.js

@@ -0,0 +1,11 @@
+function f() {
+  var a = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : 2;
+  var b = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 3;
+  return function () {
+    var _a = {
+      a: 4
+    },
+        a = _a.a;
+    return a + b;
+  }();
+}