source: frontend/node_modules/enhanced-resolve/lib/FileExistsPlugin.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 FileExistsPlugin {
        /**
         * @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);
                const fs = resolver.fileSystem;
                resolver
                        .getHook(this.source)
                        .tapAsync("FileExistsPlugin", (request, resolveContext, callback) => {
                                const file = request.path;
                                if (!file) return callback();
                                fs.stat(file, (err, stat) => {
                                        // Combine the two miss branches: a stat failure and a
                                        // "not a file" 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.isFile()) {
                                                if (resolveContext.missingDependencies) {
                                                        resolveContext.missingDependencies.add(file);
                                                }
                                                if (resolveContext.log) {
                                                        resolveContext.log(
                                                                err || !stat
                                                                        ? `${file} doesn't exist`
                                                                        : `${file} is not a file`,
                                                        );
                                                }
                                                return callback();
                                        }
                                        if (resolveContext.fileDependencies) {
                                                resolveContext.fileDependencies.add(file);
                                        }
                                        resolver.doResolve(
                                                target,
                                                request,
                                                `existing file: ${file}`,
                                                resolveContext,
                                                callback,
                                        );
                                });
                        });
        }
};