node_modules/import-local/index.js

'use strict';
const path = require('path');
const {fileURLToPath} = require('url');
const resolveCwd = require('resolve-cwd');
const pkgDir = require('pkg-dir');

module.exports = filename => {
	const normalizedFilename = filename.startsWith('file://') ? fileURLToPath(filename) : filename;
	const globalDir = pkgDir.sync(path.dirname(normalizedFilename));
	const relativePath = path.relative(globalDir, normalizedFilename);
	const pkg = require(path.join(globalDir, 'package.json'));
	const localFile = resolveCwd.silent(path.join(pkg.name, relativePath));
	const localNodeModules = path.join(process.cwd(), 'node_modules');

	const filenameInLocalNodeModules = !path.relative(localNodeModules, normalizedFilename).startsWith('..') &&
		// On Windows, if `localNodeModules` and `normalizedFilename` are on different partitions, `path.relative()` returns the value of `normalizedFilename`, resulting in `filenameInLocalNodeModules` incorrectly becoming `true`.
		path.parse(localNodeModules).root === path.parse(normalizedFilename).root;

	// Use `path.relative()` to detect local package installation,
	// because __filename's case is inconsistent on Windows
	// Can use `===` when targeting Node.js 8
	// See https://github.com/nodejs/node/issues/6624
	return !filenameInLocalNodeModules && localFile && path.relative(localFile, normalizedFilename) !== '' && require(localFile);
};