Use `require.resolve` rather than `path.resolve(__dirname, ...)` to find files

Summary: Here, we change the mechanism of finding files from `path.resolve(__dirname, ...)` to `require.resolve(...)`. The latter depends on the location of one file rather than two, and is usually more readable and intention revealing.

Reviewed By: cpojer

Differential Revision: D7858479

fbshipit-source-id: 98373cc0860faa791e60d5f11502d762fd22a409

packages/metro/src/JSTransformer/worker/__tests__/worker-test.js

@@ -30,7 +30,7 @@ describe('code transformation worker:', () => {
       'arbitrary/file.js',
       `local/file.js`,
       'someReallyArbitrary(code)',
-      path.join(__dirname, '../../../transformer.js'),
+      require.resolve('metro/src/transformer.js'),
       true,
       {
         dev: true,
@@ -59,7 +59,7 @@ describe('code transformation worker:', () => {
       'arbitrary/file.js',
       `local/file.js`,
       'arbitrary(code)',
-      path.join(__dirname, '../../../transformer.js'),
+      require.resolve('metro/src/transformer.js'),
       false,
       {
         dev: true,
@@ -94,7 +94,7 @@ describe('code transformation worker:', () => {
         'const b = require("b");',
         'import c from "./c";',
       ].join('\n'),
-      path.join(__dirname, '../../../transformer.js'),
+      require.resolve('metro/src/transformer.js'),
       false,
       {
         dev: true,

packages/metro/src/lib/__tests__/getTransformCacheKeyFn-test.js

@@ -16,7 +16,6 @@ jest.mock('../../../package.json', () => ({
 }));
 
 const getTransformCacheKeyFn = require('../getTransformCacheKeyFn');
-const path = require('path');
 
 describe('getTransformCacheKeyFn', () => {
   it('Should return always the same key for the same params', async () => {
@@ -26,10 +25,7 @@ describe('getTransformCacheKeyFn', () => {
         cacheVersion: '1.0',
         dynamicDepsInPackages: 'arbitrary',
         projectRoots: [__dirname],
-        transformModulePath: path.resolve(
-          __dirname,
-          '../../defaultTransform.js',
-        ),
+        transformModulePath: require.resolve('metro/src/defaultTransform.js'),
       })(),
     ).toMatchSnapshot();
   });
@@ -40,7 +36,7 @@ describe('getTransformCacheKeyFn', () => {
       cacheVersion: '1.0',
       dynamicDepsInPackages: 'arbitrary',
       projectRoots: [__dirname],
-      transformModulePath: path.resolve(__dirname, '../../defaultTransform.js'),
+      transformModulePath: require.resolve('metro/src/defaultTransform.js'),
     };
 
     const changedParams = [
@@ -54,10 +50,7 @@ describe('getTransformCacheKeyFn', () => {
       },
       {
         ...baseParams,
-        transformModulePath: path.resolve(
-          __dirname,
-          '../../../src/transformer.js',
-        ),
+        transformModulePath: require.resolve('metro/src/transformer.js'),
       },
     ];
 

packages/metro/src/lib/getPreludeCode.js

@@ -29,7 +29,7 @@ function getPreludeCode({
 }
 
 function formatExtraVars(extraVars) {
-  let assignments = [];
+  const assignments = [];
   for (const key in extraVars) {
     assignments.push(`${key}=${JSON.stringify(extraVars[key])}`);
   }

packages/metro/src/transformer.js

@@ -60,7 +60,7 @@ const getBabelRC = (function() {
     // use the Babel config provided with react-native.
     if (!projectBabelRCPath || !fs.existsSync(projectBabelRCPath)) {
       babelRC = json5.parse(
-        fs.readFileSync(path.resolve(__dirname, '..', 'rn-babelrc.json')),
+        fs.readFileSync(require.resolve('metro/rn-babelrc.json')),
       );
 
       // Require the babel-preset's listed in the default babel config