use parse method from transform context

package.json

@@ -21,13 +21,13 @@
     "README.md"
   ],
   "dependencies": {
-    "acorn": "^5.2.1",
     "estree-walker": "^0.5.0",
     "magic-string": "^0.22.4",
     "resolve": "^1.4.0",
     "rollup-pluginutils": "^2.0.1"
   },
   "devDependencies": {
+    "acorn": "^5.2.1",
     "eslint": "^4.8.0",
     "locate-character": "^2.0.1",
     "mocha": "^4.0.1",

src/index.js

@@ -169,7 +169,7 @@ export default function commonjs ( options = {} ) {
 			if ( extensions.indexOf( extname( id ) ) === -1 ) return null;
 
 			return entryModuleIdsPromise.then( (entryModuleIds) => {
-				const {isEsModule, hasDefaultExport, ast} = checkEsModule( code, id );
+				const {isEsModule, hasDefaultExport, ast} = checkEsModule( this.parse, code, id );
 				if ( isEsModule ) {
 					if ( !hasDefaultExport )
 						esModulesWithoutDefaultExport.push( id );
@@ -182,7 +182,7 @@ export default function commonjs ( options = {} ) {
 					return;
 				}
 
-				const transformed = transformCommonjs( code, id, entryModuleIds.indexOf(id) !== -1, ignoreGlobal, ignoreRequire, customNamedExports[ id ], sourceMap, allowDynamicRequire, ast );
+				const transformed = transformCommonjs( this.parse, code, id, entryModuleIds.indexOf(id) !== -1, ignoreGlobal, ignoreRequire, customNamedExports[ id ], sourceMap, allowDynamicRequire, ast );
 				if ( !transformed ) return;
 
 				commonjsModules.set( id, true );

src/transform.js

@@ -1,4 +1,3 @@
-import acorn from 'acorn';
 import { walk } from 'estree-walker';
 import MagicString from 'magic-string';
 import { attachScopes, makeLegalIdentifier } from 'rollup-pluginutils';
@@ -26,9 +25,9 @@ function deconflict ( scope, globals, identifier ) {
 	return deconflicted;
 }
 
-function tryParse ( code, id ) {
+function tryParse ( parse, code, id ) {
 	try {
-		return acorn.parse( code, {
+		return parse( code, {
 			ecmaVersion: 8,
 			sourceType: 'module',
 			allowReturnOutsideFunction: true
@@ -44,8 +43,8 @@ export function checkFirstpass (code, ignoreGlobal) {
 	return firstpass.test(code);
 }
 
-export function checkEsModule (code, id) {
-	const ast = tryParse(code, id);
+export function checkEsModule ( parse, code, id ) {
+	const ast = tryParse( parse, code, id );
 
 	// if there are top-level import/export declarations, this is ES not CommonJS
 	let hasDefaultExport = false;
@@ -60,8 +59,8 @@ export function checkEsModule (code, id) {
 	return { isEsModule, hasDefaultExport, ast };
 }
 
-export function transformCommonjs ( code, id, isEntry, ignoreGlobal, ignoreRequire, customNamedExports, sourceMap, allowDynamicRequire, astCache ) {
-	const ast = astCache || tryParse( code, id );
+export function transformCommonjs ( parse, code, id, isEntry, ignoreGlobal, ignoreRequire, customNamedExports, sourceMap, allowDynamicRequire, astCache ) {
+	const ast = astCache || tryParse( parse, code, id );
 
 	const magicString = new MagicString( code );
 

test/test.js

@@ -1,3 +1,4 @@
+const acorn = require( 'acorn' );
 const path = require( 'path' );
 const fs = require( 'fs' );
 const assert = require( 'assert' );
@@ -55,6 +56,10 @@ async function executeBundle ( bundle, { context, exports } = {} ) {
 	return execute( code, context );
 }
 
+const transformContext = {
+	parse: acorn.parse
+};
+
 describe( 'rollup-plugin-commonjs', () => {
 	describe( 'form', () => {
 		fs.readdirSync( 'form' ).forEach( dir => {
@@ -73,7 +78,7 @@ describe( 'rollup-plugin-commonjs', () => {
 				const input = fs.readFileSync( `form/${dir}/input.js`, 'utf-8' );
 				const expected = fs.readFileSync( `form/${dir}/output.js`, 'utf-8' ).trim();
 
-				return transform( input, 'input.js' ).then( transformed => {
+				return transform.call( transformContext, input, 'input.js' ).then( transformed => {
 					const actual = ( transformed ? transformed.code : input ).trim().replace( /\0/g, '' );
 					assert.equal( actual, expected );
 				});