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

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

"use strict";

const DescriptionFileUtils = require("./DescriptionFileUtils");

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

const slashCode = "/".charCodeAt(0);

// Sentinel stored in `_nameCache` when the description file either has no
// exports field (so self-reference can't apply) or no string `name`.
const NO_SELF_REF = Symbol("NoSelfRef");

module.exports = class SelfReferencePlugin {
        /**
         * @param {string | ResolveStepHook} source source
         * @param {string | string[]} fieldNamePath name path
         * @param {string | ResolveStepHook} target target
         */
        constructor(source, fieldNamePath, target) {
                this.source = source;
                this.target = target;
                this.fieldName = fieldNamePath;
                // Self-reference needs both an exports field and a `"name"` string.
                // Both are stable per description-file content, so cache the decision
                // in one WeakMap: the resolved name when self-reference is possible,
                // or `NO_SELF_REF` when it isn't. This skips the two per-resolve
                // `DescriptionFileUtils.getField` walks for hot packages.
                /** @type {WeakMap<JsonObject, string | typeof NO_SELF_REF>} */
                this._nameCache = new WeakMap();
        }

        /**
         * @param {Resolver} resolver the resolver
         * @returns {void}
         */
        apply(resolver) {
                const target = resolver.ensureHook(this.target);
                resolver
                        .getHook(this.source)
                        .tapAsync("SelfReferencePlugin", (request, resolveContext, callback) => {
                                if (!request.descriptionFileData) return callback();

                                const req = request.request;
                                if (!req) return callback();

                                const { descriptionFileData } = request;
                                let name = this._nameCache.get(descriptionFileData);
                                if (name === undefined) {
                                        // Feature is only enabled when an exports field is present
                                        const exportsField = DescriptionFileUtils.getField(
                                                descriptionFileData,
                                                this.fieldName,
                                        );
                                        if (!exportsField) {
                                                this._nameCache.set(descriptionFileData, NO_SELF_REF);
                                                return callback();
                                        }
                                        const rawName = DescriptionFileUtils.getField(
                                                descriptionFileData,
                                                "name",
                                        );
                                        if (typeof rawName !== "string") {
                                                this._nameCache.set(descriptionFileData, NO_SELF_REF);
                                                return callback();
                                        }
                                        name = rawName;
                                        this._nameCache.set(descriptionFileData, name);
                                } else if (name === NO_SELF_REF) {
                                        return callback();
                                }

                                if (
                                        req.startsWith(name) &&
                                        (req.length === name.length ||
                                                req.charCodeAt(name.length) === slashCode)
                                ) {
                                        const remainingRequest = `.${req.slice(name.length)}`;
                                        /** @type {ResolveRequest} */
                                        const obj = {
                                                ...request,
                                                request: remainingRequest,
                                                path: /** @type {string} */ (request.descriptionFileRoot),
                                                relativePath: ".",
                                        };

                                        resolver.doResolve(
                                                target,
                                                obj,
                                                "self reference",
                                                resolveContext,
                                                callback,
                                        );
                                } else {
                                        return callback();
                                }
                        });
        }
};