index.js

import {dirname, extname, join, normalize, resolve, sep} from 'path';
import builtinList from 'builtin-modules';
import resolveId from 'resolve';
import isModule from 'is-module';
import fs, { realpathSync } from 'fs';
import {createFilter} from 'rollup-pluginutils';
import {peerDependencies} from '../package.json';

const builtins = new Set(builtinList);

const ES6_BROWSER_EMPTY = '\0node-resolve:empty.js';
// It is important that .mjs occur before .js so that Rollup will interpret npm modules
// which deploy both ESM .mjs and CommonJS .js files as ESM.
const DEFAULT_EXTS = [ '.mjs', '.js', '.json', '.node' ];

const existsAsync = file => new Promise(fulfil => fs.exists(file, fulfil));

const readFileAsync = file => new Promise((fulfil, reject) => fs.readFile(file, (err, contents) => err ? reject(err) : fulfil(contents)));

const realpathAsync = file => new Promise((fulfil, reject) => fs.realpath(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)));

const cache = fn => {
	const cache = new Map();
	const wrapped = (param, done) => {
		if (cache.has(param) === false) {
			cache.set(param, fn(param).catch(err => {
				cache.delete(param);
				throw err;
			}));
		}
		return cache.get(param).then(result => done(null, result), done);
	};
	wrapped.clear = () => cache.clear();
	return wrapped;
};

const ignoreENOENT = err => {
	if (err.code === 'ENOENT') return false;
	throw err;
};

const readFileCached = cache(readFileAsync);

const isDirCached = cache(file => statAsync(file).then(stat => stat.isDirectory(), ignoreENOENT));

const isFileCached = cache(file => statAsync(file).then(stat => stat.isFile(), ignoreENOENT));

function getMainFields (options) {
	let mainFields;
	if (options.mainFields) {
		if ('module' in options || 'main' in options || 'jsnext' in options) {
			throw new Error(`node-resolve: do not use deprecated 'module', 'main', 'jsnext' options with 'mainFields'`);
		}
		mainFields = options.mainFields;
	} else {
		mainFields = [];
		[['module', 'module', true], ['jsnext', 'jsnext:main', false], ['main', 'main', true]].forEach(([option, field, defaultIncluded]) => {
			if (option in options) {
				// eslint-disable-next-line no-console
				console.warn(`node-resolve: setting options.${option} is deprecated, please override options.mainFields instead`);
				if (options[option]) {
					mainFields.push(field);
				}
			} else if (defaultIncluded) {
				mainFields.push(field);
			}
		});
	}
	if (options.browser && mainFields.indexOf('browser') === -1) {
		return ['browser'].concat(mainFields);
	}
	if ( !mainFields.length ) {
		throw new Error( `Please ensure at least one 'mainFields' value is specified` );
	}
	return mainFields;
}

const alwaysNull = () => null;

const resolveIdAsync = (file, opts) => new Promise((fulfil, reject) => resolveId(file, opts, (err, contents) => err ? reject(err) : fulfil(contents)));

// Resolve module specifiers in order. Promise resolves to the first
// module that resolves successfully, or the error that resulted from
// the last attempted module resolution.
function resolveImportSpecifiers (importSpecifierList, resolveOptions) {
	let p = Promise.resolve();
	for (let i = 0; i < importSpecifierList.length; i++) {
		p = p.then(v => {
			// if we've already resolved to something, just return it.
			if (v) return v;

			return resolveIdAsync(importSpecifierList[i], resolveOptions);
		});

		if (i < importSpecifierList.length - 1) {
			// swallow MODULE_NOT_FOUND errors from all but the last resolution
			p = p.catch(err => {
				if (err.code !== 'MODULE_NOT_FOUND') {
					throw err;
				}
			});
		}
	}

	return p;
}

export default function nodeResolve ( options = {} ) {
	const mainFields = getMainFields(options);
	const useBrowserOverrides = mainFields.indexOf('browser') !== -1;
	const dedupe = options.dedupe || [];
	const isPreferBuiltinsSet = options.preferBuiltins === true || options.preferBuiltins === false;
	const preferBuiltins = isPreferBuiltinsSet ? options.preferBuiltins : true;
	const customResolveOptions = options.customResolveOptions || {};
	const jail = options.jail;
	const only = Array.isArray(options.only)
		? options.only.map(o => o instanceof RegExp
			? o
			: new RegExp('^' + String(o).replace(/[\\^$*+?.()|[\]{}]/g, '\\$&') + '$')
		)
		: null;
	const browserMapCache = new Map();

	if ( options.skip ) {
		throw new Error( 'options.skip is no longer supported — you should use the main Rollup `external` option instead' );
	}

	const extensions = options.extensions || DEFAULT_EXTS;
	const packageInfoCache = new Map();
	const idToPackageInfo = new Map();

	const shouldDedupe = typeof dedupe === 'function'
		? dedupe
		: importee => dedupe.includes(importee);

	function getCachedPackageInfo (pkg, pkgPath) {
		if (packageInfoCache.has(pkgPath)) {
			return packageInfoCache.get(pkgPath);
		}

		// browserify/resolve doesn't realpath paths returned in its packageFilter callback
		if (!preserveSymlinks) {
			pkgPath = realpathSync(pkgPath);
		}

		const pkgRoot = dirname( pkgPath );

		const packageInfo = {
			// copy as we are about to munge the `main` field of `pkg`.
			packageJson: Object.assign({}, pkg),

			// path to package.json file
			packageJsonPath: pkgPath,
			
			// directory containing the package.json
			root: pkgRoot,

			// which main field was used during resolution of this module (main, module, or browser)
			resolvedMainField: 'main',

			// whether the browser map was used to resolve the entry point to this module
			browserMappedMain: false,

			// the entry point of the module with respect to the selected main field and any
			// relevant browser mappings.
			resolvedEntryPoint: ''
		};

		let overriddenMain = false;
		for ( let i = 0; i < mainFields.length; i++ ) {
			const field = mainFields[i];
			if ( typeof pkg[ field ] === 'string' ) {
				pkg[ 'main' ] = pkg[ field ];
				packageInfo.resolvedMainField = field;
				overriddenMain = true;
				break;
			}
		}

		const internalPackageInfo = {
			cachedPkg: pkg,
			hasModuleSideEffects: alwaysNull,
			hasPackageEntry: overriddenMain !== false || mainFields.indexOf( 'main' ) !== -1,
			packageBrowserField: useBrowserOverrides && typeof pkg[ 'browser' ] === 'object' &&
				Object.keys(pkg[ 'browser' ]).reduce((browser, key) => {
					let resolved = pkg[ 'browser' ][ key ];
					if (resolved && resolved[0] === '.') {
						resolved = resolve( pkgRoot, resolved );
					}
					browser[ key ] = resolved;
					if ( key[0] === '.' ) {
						const absoluteKey = resolve( pkgRoot, key );
						browser[ absoluteKey ] = resolved;
						if ( !extname(key) ) {
							extensions.reduce( ( browser, ext ) => {
								browser[ absoluteKey + ext ] = browser[ key ];
								return browser;
							}, browser );
						}
					}
					return browser;
				}, {}),
			packageInfo
		};

		const browserMap = internalPackageInfo.packageBrowserField;
		if (useBrowserOverrides && typeof pkg['browser'] === 'object' && browserMap.hasOwnProperty(pkg.main)) {
			packageInfo.resolvedEntryPoint = browserMap[pkg.main];
			packageInfo.browserMappedMain = true;
		} else {
			// index.node is technically a valid default entrypoint as well...
			packageInfo.resolvedEntryPoint = resolve(pkgRoot, pkg.main || 'index.js');
			packageInfo.browserMappedMain = false;
		}

		const packageSideEffects = pkg['sideEffects'];
		if (typeof packageSideEffects === 'boolean') {
			internalPackageInfo.hasModuleSideEffects = () => packageSideEffects;
		} else if (Array.isArray(packageSideEffects)) {
			internalPackageInfo.hasModuleSideEffects = createFilter(packageSideEffects, null, {resolve: pkgRoot});
		}

		packageInfoCache.set(pkgPath, internalPackageInfo);
		return internalPackageInfo;
	}

	let preserveSymlinks;

	return {
		name: 'node-resolve',

		buildStart ( options ) {
			preserveSymlinks = options.preserveSymlinks;
			const [major, minor] = this.meta.rollupVersion.split('.').map(Number);
			const minVersion = peerDependencies.rollup.slice(2);
			const [minMajor, minMinor] = minVersion.split('.').map(Number);
			if (major < minMajor || (major === minMajor && minor < minMinor)) {
				this.error(
					`Insufficient Rollup version: "rollup-plugin-node-resolve" requires at least rollup@${minVersion} but found rollup@${
						this.meta.rollupVersion
					}.`
				);
			}
		},

		generateBundle () {
			readFileCached.clear();
			isFileCached.clear();
			isDirCached.clear();
		},

		resolveId ( importee, importer ) {
			if (importee === ES6_BROWSER_EMPTY) {
				return importee;
			}

			if ( /\0/.test( importee ) ) return null; // ignore IDs with null character, these belong to other plugins

			const basedir = importer ? dirname( importer ) : process.cwd();

			if (shouldDedupe(importee)) {
				importee = join(process.cwd(), 'node_modules', importee);
			}

			// https://github.com/defunctzombie/package-browser-field-spec
			const browser = browserMapCache.get(importer);
			if (useBrowserOverrides && browser) {
				const resolvedImportee = resolve( basedir, importee );
				if (browser[importee] === false || browser[resolvedImportee] === false) {
					return ES6_BROWSER_EMPTY;
				}
				const browserImportee = browser[importee] || browser[resolvedImportee] || browser[resolvedImportee + '.js'] || browser[resolvedImportee + '.json'];
				if (browserImportee) {
					importee = browserImportee;
				}
			}

			const parts = importee.split( /[/\\]/ );
			let id = parts.shift();

			if ( id[0] === '@' && parts.length > 0 ) {
				// scoped packages
				id += `/${parts.shift()}`;
			} else if ( id[0] === '.' ) {
				// an import relative to the parent dir of the importer
				id = resolve( basedir, importee );
			}

			if (only && !only.some(pattern => pattern.test(id))) return null;

			let hasModuleSideEffects = alwaysNull;
			let hasPackageEntry = true;
			let packageBrowserField = false;
			let packageInfo = undefined;

			const resolveOptions = {
				basedir,
				packageFilter ( pkg, pkgPath ) {
					let cachedPkg;
					({packageInfo, cachedPkg, hasModuleSideEffects, hasPackageEntry, packageBrowserField} =
						getCachedPackageInfo(pkg, pkgPath));
					
					return cachedPkg;
				},
				readFile: readFileCached,
				isFile: isFileCached,
				isDirectory: isDirCached,
				extensions: extensions
			};

			if (preserveSymlinks !== undefined) {
				resolveOptions.preserveSymlinks = preserveSymlinks;
			}

			const importSpecifierList = [];

			if (importer === undefined && !importee[0].match(/^\.?\.?\//)) {
				// For module graph roots (i.e. when importer is undefined), we
				// need to handle 'path fragments` like `foo/bar` that are commonly
				// found in rollup config files. If importee doesn't look like a
				// relative or absolute path, we make it relative and attempt to
				// resolve it. If we don't find anything, we try resolving it as we
				// got it.
				importSpecifierList.push('./' + importee);
			}

			const importeeIsBuiltin = builtins.has(importee);

			if (importeeIsBuiltin && (!preferBuiltins || !isPreferBuiltinsSet)) {
				// The `resolve` library will not resolve packages with the same
				// name as a node built-in module. If we're resolving something
				// that's a builtin, and we don't prefer to find built-ins, we
				// first try to look up a local module with that name. If we don't
				// find anything, we resolve the builtin which just returns back
				// the built-in's name.
				importSpecifierList.push(importee + '/');
			}

			importSpecifierList.push(importee);
			return resolveImportSpecifiers(
				importSpecifierList,
				Object.assign(resolveOptions, customResolveOptions)
			)
				.then(resolved => {
					if ( resolved && packageBrowserField ) {
						if ( Object.prototype.hasOwnProperty.call(packageBrowserField,resolved) ) {
							if (!packageBrowserField[resolved]) {
								browserMapCache.set(resolved, packageBrowserField);
								return ES6_BROWSER_EMPTY;
							}
							resolved = packageBrowserField[ resolved ];
						}
						browserMapCache.set(resolved, packageBrowserField);
					}

					if ( hasPackageEntry && !preserveSymlinks && resolved ) {
						return existsAsync( resolved )
							.then(exists => exists ? realpathAsync( resolved ) : resolved);
					}
					return resolved;
				})
				.then(resolved => {
					idToPackageInfo.set(resolved, packageInfo);

					if ( hasPackageEntry ) {
						if (builtins.has(resolved) && preferBuiltins && isPreferBuiltinsSet) {
							return null;
						} else if (importeeIsBuiltin && preferBuiltins) {
							if ( !isPreferBuiltinsSet ) {
								this.warn(
									`preferring built-in module '${importee}' over local alternative ` +
									`at '${resolved}', pass 'preferBuiltins: false' to disable this ` +
									`behavior or 'preferBuiltins: true' to disable this warning`
								);
							}
							return null;
						} else if ( jail && resolved.indexOf( normalize( jail.trim( sep ) ) ) !== 0 ) {
							return null;
						}
					}

					if ( resolved && options.modulesOnly ) {
						return readFileAsync( resolved, 'utf-8')
							.then(code => isModule( code ) ? {id: resolved, moduleSideEffects: hasModuleSideEffects(resolved)} : null);
					} else {
						return {id: resolved, moduleSideEffects: hasModuleSideEffects(resolved)};
					}
				})
				.catch(() => null);
		},

		load ( importee ) {
			if ( importee === ES6_BROWSER_EMPTY ) {
				return 'export default {};';
			}
			return null;
		},

		getPackageInfoForId (id) {
			return idToPackageInfo.get(id);
		}
	};
}