source: frontend/node_modules/enhanced-resolve/lib/DirectoryExistsPlugin.js

/*
        MIT License http://www.opensource.org/licenses/mit-license.php
        Author Tobias Koppers @sokra
*/

"use strict";

/** @typedef {import("./Resolver")} Resolver */
/** @typedef {import("./Resolver").ResolveStepHook} ResolveStepHook */

module.exports = class DirectoryExistsPlugin {
        /**
         * @param {string | ResolveStepHook} source source
         * @param {string | ResolveStepHook} target target
         */
        constructor(source, target) {
                this.source = source;
                this.target = target;
        }

        /**
         * @param {Resolver} resolver the resolver
         * @returns {void}
         */
        apply(resolver) {
                const target = resolver.ensureHook(this.target);
                resolver
                        .getHook(this.source)
                        .tapAsync(
                                "DirectoryExistsPlugin",
                                (request, resolveContext, callback) => {
                                        const fs = resolver.fileSystem;
                                        const directory = request.path;
                                        if (!directory) return callback();
                                        fs.stat(directory, (err, stat) => {
                                                // Combine the two miss branches: a stat failure and a
                                                // "not a directory" result share the same handling — record
                                                // the path on `missingDependencies`, log the right reason,
                                                // then bail. The error-message ternary picks the wording
                                                // that matched the failing condition.
                                                if (err || !stat || !stat.isDirectory()) {
                                                        if (resolveContext.missingDependencies) {
                                                                resolveContext.missingDependencies.add(directory);
                                                        }
                                                        if (resolveContext.log) {
                                                                resolveContext.log(
                                                                        err || !stat
                                                                                ? `${directory} doesn't exist`
                                                                                : `${directory} is not a directory`,
                                                                );
                                                        }
                                                        return callback();
                                                }
                                                if (resolveContext.fileDependencies) {
                                                        resolveContext.fileDependencies.add(directory);
                                                }
                                                resolver.doResolve(
                                                        target,
                                                        request,
                                                        `existing directory ${directory}`,
                                                        resolveContext,
                                                        callback,
                                                );
                                        });
                                },
                        );
        }
};