perf: cache file stats/reads

Author: keithamus

src/index.js

@@ -8,6 +8,33 @@ const ES6_BROWSER_EMPTY = resolve( __dirname, '../src/empty.js' );
 const CONSOLE_WARN = ( ...args ) => console.warn( ...args ); // eslint-disable-line no-console
 const exts = [ '.js', '.json', '.node' ];
 
+let readFileCache = {};
+const readFileAsync = file => new Promise((fulfil, reject) => fs.readFile(file, (err, contents) => err ? reject(err) : fulfil(contents)));
+const statAsync = file => new Promise((fulfil, reject) => fs.stat(file, (err, contents) => err ? reject(err) : fulfil(contents)));
+function cachedReadFile (file, cb) {
+	if (file in readFileCache === false) {
+		readFileCache[file] = readFileAsync(file).catch(err => {
+			delete readFileCache[file];
+			throw err;
+		});
+	}
+	readFileCache[file].then(contents => cb(null, contents), cb);
+}
+
+let isFileCache = {};
+function cachedIsFile (file, cb) {
+	if (file in isFileCache === false) {
+		isFileCache[file] = statAsync(file)
+			.then(stat => stat.isFile())
+			.catch(err => {
+				if (err.code == 'ENOENT') return false;
+				delete isFileCache[file];
+				throw err;
+			});
+	}
+	isFileCache[file].then(contents => cb(null, contents), cb);
+}
+
 export default function nodeResolve ( options = {} ) {
 	const useModule = options.module !== false;
 	const useMain = options.main !== false;
@@ -31,6 +58,11 @@ export default function nodeResolve ( options = {} ) {
 	return {
 		name: 'node-resolve',
 
+		write () {
+			isFileCache = {}
+			readFileCache = {}
+		},
+
 		resolveId ( importee, importer ) {
 			if ( /\0/.test( importee ) ) return null; // ignore IDs with null character, these belong to other plugins
 
@@ -99,6 +131,8 @@ export default function nodeResolve ( options = {} ) {
 							}
 							return pkg;
 						},
+						readFile: cachedReadFile,
+						isFile: cachedIsFile,
 						extensions: options.extensions
 					}, customResolveOptions ),
 					( err, resolved ) => {