🚀 Change const to let VariableDeclarations for ESM Output (#26727)

* Babel plugin for const -> let

build-system/babel-plugins/babel-plugin-const-transformer/index.js

@@ -0,0 +1,35 @@
+/**
+ * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Changes the
+ * The above said variables are in src/mode.js file.
+ * @param {Object} babelTypes
+ * @return {!Object}
+ */
+module.exports = function({types: t}) {
+  return {
+    visitor: {
+      VariableDeclaration(path) {
+        if (path.node.kind !== 'const') {
+          return;
+        }
+
+        path.replaceWith(t.variableDeclaration('let', path.node.declarations));
+      },
+    },
+  };
+};

build-system/babel-plugins/babel-plugin-const-transformer/test/fixtures/transform-assertions/ignored-let/input.js

@@ -0,0 +1,40 @@
+/**
+ * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+let foo = true;
+let bar = 1;
+let baz = NaN;
+let yep = 'hello';
+let another = {};
+let array = [];
+
+function thing() {
+  let foo = true;
+  let bar = 1;
+  let baz = NaN;
+  let yep = 'hello';
+  let another = {};
+  let array = [];
+}
+
+thing: {
+  let foo = true;
+  let bar = 1;
+  let baz = NaN;
+  let yep = 'hello';
+  let another = {};
+  let array = [];
+}

build-system/babel-plugins/babel-plugin-const-transformer/test/fixtures/transform-assertions/ignored-let/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["../../../../../babel-plugin-const-transformer"]
+}

build-system/babel-plugins/babel-plugin-const-transformer/test/fixtures/transform-assertions/ignored-let/output.js

@@ -0,0 +1,39 @@
+/**
+ * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+let foo = true;
+let bar = 1;
+let baz = NaN;
+let yep = 'hello';
+let another = {};
+let array = [];
+
+function thing() {
+  let foo = true;
+  let bar = 1;
+  let baz = NaN;
+  let yep = 'hello';
+  let another = {};
+  let array = [];
+}
+
+thing: {
+  let foo = true;
+  let bar = 1;
+  let baz = NaN;
+  let yep = 'hello';
+  let another = {};
+  let array = [];
+}

build-system/babel-plugins/babel-plugin-const-transformer/test/fixtures/transform-assertions/ignored-var/input.js

@@ -0,0 +1,40 @@
+/**
+ * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+var foo = true;
+var bar = 1;
+var baz = NaN;
+var yep = 'hello';
+var another = {};
+var array = [];
+
+function thing() {
+  var foo = true;
+  var bar = 1;
+  var baz = NaN;
+  var yep = 'hello';
+  var another = {};
+  var array = [];
+}
+
+thing: {
+  var foo = true;
+  var bar = 1;
+  var baz = NaN;
+  var yep = 'hello';
+  var another = {};
+  var array = [];
+}

build-system/babel-plugins/babel-plugin-const-transformer/test/fixtures/transform-assertions/ignored-var/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["../../../../../babel-plugin-const-transformer"]
+}

build-system/babel-plugins/babel-plugin-const-transformer/test/fixtures/transform-assertions/ignored-var/output.js

@@ -0,0 +1,39 @@
+/**
+ * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+var foo = true;
+var bar = 1;
+var baz = NaN;
+var yep = 'hello';
+var another = {};
+var array = [];
+
+function thing() {
+  var foo = true;
+  var bar = 1;
+  var baz = NaN;
+  var yep = 'hello';
+  var another = {};
+  var array = [];
+}
+
+thing: {
+  var foo = true;
+  var bar = 1;
+  var baz = NaN;
+  var yep = 'hello';
+  var another = {};
+  var array = [];
+}

build-system/babel-plugins/babel-plugin-const-transformer/test/fixtures/transform-assertions/should-transform/input.js

@@ -0,0 +1,40 @@
+/**
+ * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const foo = true;
+const bar = 1;
+const baz = NaN;
+const yep = 'hello';
+const another = {};
+const array = [];
+
+function thing() {
+  const foo = true;
+  const bar = 1;
+  const baz = NaN;
+  const yep = 'hello';
+  const another = {};
+  const array = [];
+}
+
+thing: {
+  const foo = true;
+  const bar = 1;
+  const baz = NaN;
+  const yep = 'hello';
+  const another = {};
+  const array = [];
+}

build-system/babel-plugins/babel-plugin-const-transformer/test/fixtures/transform-assertions/should-transform/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["../../../../../babel-plugin-const-transformer"]
+}

build-system/babel-plugins/babel-plugin-const-transformer/test/fixtures/transform-assertions/should-transform/output.js

@@ -0,0 +1,39 @@
+/**
+ * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+let foo = true;
+let bar = 1;
+let baz = NaN;
+let yep = 'hello';
+let another = {};
+let array = [];
+
+function thing() {
+  let foo = true;
+  let bar = 1;
+  let baz = NaN;
+  let yep = 'hello';
+  let another = {};
+  let array = [];
+}
+
+thing: {
+  let foo = true;
+  let bar = 1;
+  let baz = NaN;
+  let yep = 'hello';
+  let another = {};
+  let array = [];
+}

build-system/babel-plugins/babel-plugin-const-transformer/test/index.js

@@ -0,0 +1,19 @@
+/**
+ * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const runner = require('@babel/helper-plugin-test-runner').default;
+
+runner(__dirname);