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

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

@@ -0,0 +1,152 @@
+/**
+ * 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 fs from 'fs-extra';
+import logger from '@docusaurus/logger';
+import {escapePath, type WebpackCompilerName} from '@docusaurus/utils';
+import {getProcessor, type SimpleProcessorResult} from './processor';
+import {validateMDXFrontMatter} from './frontMatter';
+import preprocessor from './preprocessor';
+import type {Options} from './loader';
+
+/**
+ * When this throws, it generally means that there's no metadata file associated
+ * with this MDX document. It can happen when using MDX partials (usually
+ * starting with _). That's why it's important to provide the `isMDXPartial`
+ * function in config
+ */
+export async function readMetadataPath(metadataPath: string): Promise<string> {
+  try {
+    return await fs.readFile(metadataPath, 'utf8');
+  } catch (error) {
+    throw new Error(
+      logger.interpolate`MDX loader can't read MDX metadata file path=${metadataPath}. Maybe the isMDXPartial option function was not provided?`,
+      {cause: error as Error},
+    );
+  }
+}
+
+/**
+ * Converts assets an object with Webpack require calls code.
+ * This is useful for mdx files to reference co-located assets using relative
+ * paths. Those assets should enter the Webpack assets pipeline and be hashed.
+ * For now, we only handle that for images and paths starting with `./`:
+ *
+ * `{image: "./myImage.png"}` => `{image: require("./myImage.png")}`
+ */
+export function createAssetsExportCode({
+  assets,
+  inlineMarkdownAssetImageFileLoader,
+}: {
+  assets: unknown;
+  inlineMarkdownAssetImageFileLoader: string;
+}): string {
+  if (
+    typeof assets !== 'object' ||
+    !assets ||
+    Object.keys(assets).length === 0
+  ) {
+    return 'undefined';
+  }
+
+  // TODO implementation can be completed/enhanced
+  function createAssetValueCode(assetValue: unknown): string | undefined {
+    if (Array.isArray(assetValue)) {
+      const arrayItemCodes = assetValue.map(
+        (item: unknown) => createAssetValueCode(item) ?? 'undefined',
+      );
+      return `[${arrayItemCodes.join(', ')}]`;
+    }
+    // Only process string values starting with ./
+    // We could enhance this logic and check if file exists on disc?
+    if (typeof assetValue === 'string' && assetValue.startsWith('./')) {
+      // TODO do we have other use-cases than image assets?
+      // Probably not worth adding more support, as we want to move to Webpack 5 new asset system (https://github.com/facebook/docusaurus/pull/4708)
+      return `require("${inlineMarkdownAssetImageFileLoader}${escapePath(
+        assetValue,
+      )}").default`;
+    }
+    return undefined;
+  }
+
+  const assetEntries = Object.entries(assets);
+
+  const codeLines = assetEntries
+    .map(([key, value]: [string, unknown]) => {
+      const assetRequireCode = createAssetValueCode(value);
+      return assetRequireCode ? `"${key}": ${assetRequireCode},` : undefined;
+    })
+    .filter(Boolean);
+
+  return `{\n${codeLines.join('\n')}\n}`;
+}
+
+/**
+ * data.contentTitle is set by the remark contentTitle plugin
+ */
+export function extractContentTitleData(data: {
+  [key: string]: unknown;
+}): string | undefined {
+  return data.contentTitle as string | undefined;
+}
+
+export async function compileToJSX({
+  filePath,
+  fileContent,
+  frontMatter,
+  options,
+  compilerName,
+}: {
+  filePath: string;
+  fileContent: string;
+  frontMatter: Record<string, unknown>;
+  options: Options;
+  compilerName: WebpackCompilerName;
+}): Promise<SimpleProcessorResult> {
+  const preprocessedFileContent = preprocessor({
+    fileContent,
+    filePath,
+    admonitions: options.admonitions,
+    markdownConfig: options.markdownConfig,
+  });
+
+  const mdxFrontMatter = validateMDXFrontMatter(frontMatter.mdx);
+
+  const processor = await getProcessor({
+    filePath,
+    options,
+    mdxFrontMatter,
+  });
+
+  try {
+    return await processor.process({
+      content: preprocessedFileContent,
+      filePath,
+      frontMatter,
+      compilerName,
+    });
+  } catch (errorUnknown) {
+    const error = errorUnknown as Error;
+
+    // MDX can emit errors that have useful extra attributes
+    const errorJSON = JSON.stringify(error, null, 2);
+    const errorDetails =
+      errorJSON === '{}'
+        ? // regular JS error case: print stacktrace
+          error.stack ?? 'N/A'
+        : // MDX error: print extra attributes + stacktrace
+          `${errorJSON}\n${error.stack}`;
+
+    throw new Error(
+      `MDX compilation failed for file ${logger.path(filePath)}\nCause: ${
+        error.message
+      }\nDetails:\n${errorDetails}`,
+      // TODO error cause doesn't seem to be used by Webpack stats.errors :s
+      {cause: error},
+    );
+  }
+}