refactor(mdx-loader): refactor mdx-loader, expose loader creation utils (#10450)

packages/docusaurus-mdx-loader/src/createMDXLoader.ts

@@ -0,0 +1,48 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {createProcessors} from './processor';
+import type {Options} from './loader';
+import type {RuleSetRule, RuleSetUseItem} from 'webpack';
+
+async function enhancedOptions(options: Options): Promise<Options> {
+  // Because Jest doesn't like ESM / createProcessors()
+  if (process.env.N0DE_ENV === 'test' || process.env.JEST_WORKER_ID) {
+    return options;
+  }
+
+  // We create the processor earlier here, to avoid the lazy processor creating
+  // Lazy creation messes-up with Rsdoctor ability to measure mdx-loader perf
+  const newOptions: Options = options.processors
+    ? options
+    : {...options, processors: await createProcessors({options})};
+
+  return newOptions;
+}
+
+export async function createMDXLoaderItem(
+  options: Options,
+): Promise<RuleSetUseItem> {
+  return {
+    loader: require.resolve('@docusaurus/mdx-loader'),
+    options: await enhancedOptions(options),
+  };
+}
+
+export async function createMDXLoaderRule({
+  include,
+  options,
+}: {
+  include: RuleSetRule['include'];
+  options: Options;
+}): Promise<RuleSetRule> {
+  return {
+    test: /\.mdx?$/i,
+    include,
+    use: [await createMDXLoaderItem(options)],
+  };
+}