Remove some easy to remove semicolons for ASI (#321)

Author: kristoferbaxter

src/transformers/chunk/asi.ts

@@ -0,0 +1,50 @@
+/**
+ * Copyright 2018 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.
+ */
+
+import { ChunkTransform } from '../../transform';
+import { Range } from '../../types';
+import { parse } from '../../acorn';
+import MagicString from 'magic-string';
+
+export default class ASITransform extends ChunkTransform {
+  public name = 'ASITransform';
+
+  /**
+   * Small reduction in semi-colons, removing from end of block statements.
+   * @param source source following closure compiler minification
+   */
+  public async post(source: MagicString): Promise<MagicString> {
+    const code = source.toString();
+    const program = parse(code);
+
+    if (program.body) {
+      const lastStatement = program.body[program.body.length - 1];
+      if (lastStatement) {
+        const [start, end] = lastStatement.range as Range;
+        if (lastStatement.type === 'EmptyStatement') {
+          source.remove(start, end);
+        } else {
+          const lastStatementSource = code.substring(start, end);
+          if (lastStatementSource.endsWith(';')) {
+            source.overwrite(start, end, code.substring(start, end - 1));
+          }
+        }
+      }
+    }
+
+    return source;
+  }
+}

src/transformers/chunk/const.ts

@@ -31,7 +31,7 @@ export default class ConstTransform extends ChunkTransform {
    */
   public async pre(source: MagicString): Promise<MagicString> {
     const code = source.toString();
-    const program = parse(source.toString());
+    const program = parse(code);
 
     walk.simple(program, {
       VariableDeclaration(node: VariableDeclaration) {

src/transformers/chunk/transforms.ts

@@ -30,6 +30,7 @@ import ExportTransform from './exports';
 import ImportTransform from './imports';
 import StrictTransform from './strict';
 import ConstTransform from './const';
+import ASITransform from './asi';
 import { ChunkTransform, chunkLifecycle } from '../../transform';
 import { Mangle } from '../mangle';
 import { Ebbinghaus } from '../ebbinghaus';
@@ -46,6 +47,7 @@ const TRANSFORMS: Array<typeof ChunkTransform> = [
   StrictTransform,
   ExportTransform,
   ImportTransform,
+  ASITransform,
   // Acorn cannot parse content starting here.
   HashbangApplyTransform,
 ];

test/arrow-function/fixtures/multiple-arguments.esm.advanced.js

@@ -1 +1 @@
-export var multipleArguments=(a,b)=>console.log(a,b);
+export var multipleArguments=(a,b)=>console.log(a,b)

test/arrow-function/fixtures/multiple-arguments.esm.default.js

@@ -1 +1 @@
-export var multipleArguments=(a,b)=>console.log(a,b);
+export var multipleArguments=(a,b)=>console.log(a,b)

test/arrow-function/fixtures/multiple-arguments.esm.es5.js

@@ -1 +1 @@
-export function multipleArguments(a,b){return console.log(a,b)};
+export function multipleArguments(a,b){return console.log(a,b)}

test/arrow-function/fixtures/multiple-arguments.esm.pretty.js

@@ -1,2 +1,2 @@
 
-export var multipleArguments=(a, b) => console.log(a, b);
+export var multipleArguments=(a, b) => console.log(a, b)

test/arrow-function/fixtures/single-argument.esm.advanced.js

@@ -1 +1 @@
-export var singleArgument=a=>console.log(a);
+export var singleArgument=a=>console.log(a)

test/arrow-function/fixtures/single-argument.esm.default.js

@@ -1 +1 @@
-export var singleArgument=a=>console.log(a);
+export var singleArgument=a=>console.log(a)

test/arrow-function/fixtures/single-argument.esm.es5.js

@@ -1 +1 @@
-export function singleArgument(a){return console.log(a)};
+export function singleArgument(a){return console.log(a)}