loader.js

const path = require("path");

const {
  findModuleById,
  evalModuleCode,
  AUTO_PUBLIC_PATH,
  ABSOLUTE_PUBLIC_PATH,
  SINGLE_DOT_PATH_SEGMENT,
  stringifyRequest,
} = require("./utils");
const schema = require("./loader-options.json");

const MiniCssExtractPlugin = require("./index");

/** @typedef {import("schema-utils/declarations/validate").Schema} Schema */
/** @typedef {import("webpack").Compiler} Compiler */
/** @typedef {import("webpack").Compilation} Compilation */
/** @typedef {import("webpack").Chunk} Chunk */
/** @typedef {import("webpack").Module} Module */
/** @typedef {import("webpack").sources.Source} Source */
/** @typedef {import("webpack").AssetInfo} AssetInfo */
/** @typedef {import("webpack").NormalModule} NormalModule */
/** @typedef {import("./index.js").LoaderOptions} LoaderOptions */

/** @typedef {any} TODO */

/**
 * @typedef {Object} Dependency
 * @property {string} identifier
 * @property {string | null} context
 * @property {Buffer} content
 * @property {string} media
 * @property {string} [supports]
 * @property {string} [layer]
 * @property {Buffer} [sourceMap]
 */

/**
 * @param {string} content
 * @param {{ loaderContext: import("webpack").LoaderContext<LoaderOptions>, options: LoaderOptions, locals: {[key: string]: string } | undefined }} context
 * @returns {string}
 */
function hotLoader(content, context) {
  const accept = context.locals
    ? ""
    : "module.hot.accept(undefined, cssReload);";

  return `${content}
    if(module.hot) {
      // ${Date.now()}
      var cssReload = require(${stringifyRequest(
        context.loaderContext,
        path.join(__dirname, "hmr/hotModuleReplacement.js")
      )})(module.id, ${JSON.stringify({
    ...context.options,
    locals: !!context.locals,
  })});
      module.hot.dispose(cssReload);
      ${accept}
    }
  `;
}

/**
 * @this {import("webpack").LoaderContext<LoaderOptions>}
 * @param {string} request
 */
function pitch(request) {
  // @ts-ignore
  const options = this.getOptions(/** @type {Schema} */ (schema));
  const callback = this.async();
  const optionsFromPlugin = /** @type {TODO} */ (this)[
    MiniCssExtractPlugin.pluginSymbol
  ];

  if (!optionsFromPlugin) {
    callback(
      new Error(
        "You forgot to add 'mini-css-extract-plugin' plugin (i.e. `{ plugins: [new MiniCssExtractPlugin()] }`), please read https://github.com/webpack-contrib/mini-css-extract-plugin#getting-started"
      )
    );

    return;
  }

  const { webpack } = /** @type {Compiler} */ (this._compiler);

  /**
   * @param {TODO} originalExports
   * @param {Compilation} [compilation]
   * @param {{ [name: string]: Source }} [assets]
   * @param {Map<string, AssetInfo>} [assetsInfo]
   * @returns {void}
   */
  const handleExports = (originalExports, compilation, assets, assetsInfo) => {
    /** @type {{[key: string]: string } | undefined} */
    let locals;
    let namedExport;

    const esModule =
      typeof options.esModule !== "undefined" ? options.esModule : true;

    /**
     * @param {Dependency[] | [null, object][]} dependencies
     */
    const addDependencies = (dependencies) => {
      if (!Array.isArray(dependencies) && dependencies != null) {
        throw new Error(
          `Exported value was not extracted as an array: ${JSON.stringify(
            dependencies
          )}`
        );
      }

      const identifierCountMap = new Map();
      const emit = typeof options.emit !== "undefined" ? options.emit : true;
      let lastDep;

      for (const dependency of dependencies) {
        if (!(/** @type {Dependency} */ (dependency).identifier) || !emit) {
          // eslint-disable-next-line no-continue
          continue;
        }

        const count =
          identifierCountMap.get(
            /** @type {Dependency} */ (dependency).identifier
          ) || 0;
        const CssDependency = MiniCssExtractPlugin.getCssDependency(webpack);

        /** @type {NormalModule} */
        (this._module).addDependency(
          (lastDep = new CssDependency(
            /** @type {Dependency} */
            (dependency),
            /** @type {Dependency} */
            (dependency).context,
            count
          ))
        );
        identifierCountMap.set(
          /** @type {Dependency} */
          (dependency).identifier,
          count + 1
        );
      }

      if (lastDep && assets) {
        lastDep.assets = assets;
        lastDep.assetsInfo = assetsInfo;
      }
    };

    try {
      // eslint-disable-next-line no-underscore-dangle
      const exports = originalExports.__esModule
        ? originalExports.default
        : originalExports;

      namedExport =
        // eslint-disable-next-line no-underscore-dangle
        originalExports.__esModule &&
        (!originalExports.default || !("locals" in originalExports.default));

      if (namedExport) {
        Object.keys(originalExports).forEach((key) => {
          if (key !== "default") {
            if (!locals) {
              locals = {};
            }

            locals[key] = originalExports[key];
          }
        });
      } else {
        locals = exports && exports.locals;
      }

      /** @type {Dependency[] | [null, object][]} */
      let dependencies;

      if (!Array.isArray(exports)) {
        dependencies = [[null, exports]];
      } else {
        dependencies = exports.map(
          ([id, content, media, sourceMap, supports, layer]) => {
            let identifier = id;
            let context;

            if (compilation) {
              const module =
                /** @type {Module} */
                (findModuleById(compilation, id));

              identifier = module.identifier();
              ({ context } = module);
            } else {
              // TODO check if this context is used somewhere
              context = this.rootContext;
            }

            return {
              identifier,
              context,
              content: Buffer.from(content),
              media,
              supports,
              layer,
              sourceMap: sourceMap
                ? Buffer.from(JSON.stringify(sourceMap))
                : // eslint-disable-next-line no-undefined
                  undefined,
            };
          }
        );
      }

      addDependencies(dependencies);
    } catch (e) {
      callback(/** @type {Error} */ (e));

      return;
    }

    const result = locals
      ? namedExport
        ? Object.keys(locals)
            .map(
              (key) =>
                `\nexport var ${key} = ${JSON.stringify(
                  /** @type {{[key: string]: string }} */
                  (locals)[key]
                )};`
            )
            .join("")
        : `\n${
            esModule ? "export default" : "module.exports ="
          } ${JSON.stringify(locals)};`
      : esModule
      ? `\nexport {};`
      : "";

    let resultSource = `// extracted by ${MiniCssExtractPlugin.pluginName}`;

    resultSource += this.hot
      ? hotLoader(result, { loaderContext: this, options, locals })
      : result;

    callback(null, resultSource);
  };

  let { publicPath } =
    /** @type {Compilation} */
    (this._compilation).outputOptions;

  if (typeof options.publicPath === "string") {
    // eslint-disable-next-line prefer-destructuring
    publicPath = options.publicPath;
  } else if (typeof options.publicPath === "function") {
    publicPath = options.publicPath(this.resourcePath, this.rootContext);
  }

  if (publicPath === "auto") {
    publicPath = AUTO_PUBLIC_PATH;
  }

  if (
    (typeof optionsFromPlugin.experimentalUseImportModule === "undefined" &&
      typeof this.importModule === "function") ||
    optionsFromPlugin.experimentalUseImportModule
  ) {
    if (!this.importModule) {
      callback(
        new Error(
          "You are using 'experimentalUseImportModule' but 'this.importModule' is not available in loader context. You need to have at least webpack 5.33.2."
        )
      );
      return;
    }

    let publicPathForExtract;

    if (typeof publicPath === "string") {
      const isAbsolutePublicPath = /^[a-zA-Z][a-zA-Z\d+\-.]*?:/.test(
        publicPath
      );

      publicPathForExtract = isAbsolutePublicPath
        ? publicPath
        : `${ABSOLUTE_PUBLIC_PATH}${publicPath.replace(
            /\./g,
            SINGLE_DOT_PATH_SEGMENT
          )}`;
    } else {
      publicPathForExtract = publicPath;
    }

    this.importModule(
      `${this.resourcePath}.webpack[javascript/auto]!=!!!${request}`,
      {
        layer: options.layer,
        publicPath: /** @type {string} */ (publicPathForExtract),
      },
      /**
       * @param {Error | null | undefined} error
       * @param {object} exports
       */
      (error, exports) => {
        if (error) {
          callback(error);

          return;
        }

        handleExports(exports);
      }
    );
    return;
  }

  const loaders = this.loaders.slice(this.loaderIndex + 1);

  this.addDependency(this.resourcePath);

  const childFilename = "*";

  const outputOptions = {
    filename: childFilename,
    publicPath,
  };

  const childCompiler =
    /** @type {Compilation} */
    (this._compilation).createChildCompiler(
      `${MiniCssExtractPlugin.pluginName} ${request}`,
      outputOptions
    );

  // The templates are compiled and executed by NodeJS - similar to server side rendering
  // Unfortunately this causes issues as some loaders require an absolute URL to support ES Modules
  // The following config enables relative URL support for the child compiler
  childCompiler.options.module = { ...childCompiler.options.module };
  childCompiler.options.module.parser = {
    ...childCompiler.options.module.parser,
  };
  childCompiler.options.module.parser.javascript = {
    ...childCompiler.options.module.parser.javascript,
    url: "relative",
  };

  const { NodeTemplatePlugin } = webpack.node;
  const { NodeTargetPlugin } = webpack.node;

  new NodeTemplatePlugin(outputOptions).apply(childCompiler);
  new NodeTargetPlugin().apply(childCompiler);

  const { EntryOptionPlugin } = webpack;

  const {
    library: { EnableLibraryPlugin },
  } = webpack;

  new EnableLibraryPlugin("commonjs2").apply(childCompiler);

  EntryOptionPlugin.applyEntryOption(childCompiler, this.context, {
    child: {
      library: {
        type: "commonjs2",
      },
      import: [`!!${request}`],
    },
  });
  const { LimitChunkCountPlugin } = webpack.optimize;

  new LimitChunkCountPlugin({ maxChunks: 1 }).apply(childCompiler);

  const { NormalModule } = webpack;

  childCompiler.hooks.thisCompilation.tap(
    `${MiniCssExtractPlugin.pluginName} loader`,
    /**
     * @param {Compilation} compilation
     */
    (compilation) => {
      const normalModuleHook =
        NormalModule.getCompilationHooks(compilation).loader;

      normalModuleHook.tap(
        `${MiniCssExtractPlugin.pluginName} loader`,
        (loaderContext, module) => {
          if (module.request === request) {
            // eslint-disable-next-line no-param-reassign
            module.loaders = loaders.map((loader) => {
              return {
                type: null,
                loader: loader.path,
                options: loader.options,
                ident: loader.ident,
              };
            });
          }
        }
      );
    }
  );

  /** @type {string | Buffer} */
  let source;

  childCompiler.hooks.compilation.tap(
    MiniCssExtractPlugin.pluginName,
    /**
     * @param {Compilation} compilation
     */
    (compilation) => {
      compilation.hooks.processAssets.tap(
        MiniCssExtractPlugin.pluginName,
        () => {
          source =
            compilation.assets[childFilename] &&
            compilation.assets[childFilename].source();

          // Remove all chunk assets
          compilation.chunks.forEach((chunk) => {
            chunk.files.forEach((file) => {
              compilation.deleteAsset(file);
            });
          });
        }
      );
    }
  );

  childCompiler.runAsChild((error, entries, compilation) => {
    if (error) {
      callback(error);

      return;
    }

    if (/** @type {Compilation} */ (compilation).errors.length > 0) {
      callback(/** @type {Compilation} */ (compilation).errors[0]);

      return;
    }

    /** @type {{ [name: string]: Source }} */
    const assets = Object.create(null);
    /** @type {Map<string, AssetInfo>} */
    const assetsInfo = new Map();

    for (const asset of /** @type {Compilation} */ (compilation).getAssets()) {
      assets[asset.name] = asset.source;
      assetsInfo.set(asset.name, asset.info);
    }

    /** @type {Compilation} */
    (compilation).fileDependencies.forEach((dep) => {
      this.addDependency(dep);
    }, this);

    /** @type {Compilation} */
    (compilation).contextDependencies.forEach((dep) => {
      this.addContextDependency(dep);
    }, this);

    if (!source) {
      callback(new Error("Didn't get a result from child compiler"));

      return;
    }

    let originalExports;
    try {
      originalExports = evalModuleCode(this, source, request);
    } catch (e) {
      callback(/** @type {Error} */ (e));

      return;
    }

    handleExports(originalExports, compilation, assets, assetsInfo);
  });
}

module.exports = { default: function loader() {}, pitch };