check-links.mjs

import fs from "node:fs";
import readdirp from "readdirp";
import path from "node:path";
import remarkMdx from "remark-mdx";
import { remark } from "remark";
import reporter from "vfile-reporter";
import { visit } from "unist-util-visit";
import remarkFrontmatter from "remark-frontmatter";

// Some URLs are valid (e.g. they link to marketing sites or docs that are not hosted through clerk-docs) so they should be excluded from the check.
// These URLs will be used with the .startsWith() method, so they should be specific enough to not match any URLs that should be checked.
const EXCLUDE_LIST = [
  "/pricing",
  "/docs/reference/backend-api",
  "/docs/reference/frontend-api",
];

const ERRORS = {
  RELATIVE_LINK(url) {
    return `Relative link detected: ${url}. Relative links are not valid, make sure the link is absolute and starts with \`/docs/\`.`;
  },
  FILE_NOT_FOUND(url) {
    return `Matching file not found for path: ${url}. Expected file to exist at \`${
      url.split("#")[0]
    }.mdx\`.`;
  },
};

const fileCheckCache = new Map();

const validateUrl = (url, node, file) => {
  const isRelative = url.startsWith(".");
  const isAbsolute = url.startsWith("/");

  if (isRelative) {
    file.message(ERRORS.RELATIVE_LINK(url), node.position);
  } else if (isAbsolute) {
    const cleanedUrl = url.split("#")[0];

    if (!fileCheckCache.has(cleanedUrl)) {
      const isExcluded = EXCLUDE_LIST.some((excludedUrl) =>
        cleanedUrl.startsWith(excludedUrl)
      );

      // If the URL is excluded, we don't need to check the filesystem. However, we should do the check here and not early return in the beginning because we still want to cache the result.
      if (isExcluded) {
        fileCheckCache.set(cleanedUrl, true);
      } else {
        const filePath = path.join(process.cwd(), `${cleanedUrl}.mdx`);
        fileCheckCache.set(cleanedUrl, fs.existsSync(filePath));
      }
    }

    const exists = fileCheckCache.get(cleanedUrl);

    if (!exists) {
      file.message(ERRORS.FILE_NOT_FOUND(url), node.position);
    }
  }
};

// Iterates over each link in the markdown file and checks if the link is valid by checking if the file exists locally.
const remarkPluginValidateLinks = () => (tree, file) => {
  visit(
    tree,
    (node) =>
      node.type === "link" ||
      // Check known components with a link prop
      node?.attributes?.some?.((attribute) => attribute?.name === "link"),
    (node) => {
      if ("url" in node) {
        const { url } = node;
        validateUrl(url, node, file);
        return;
      }

      if (node.type !== "link") {
        const url = node.attributes.find(
          (attribute) => attribute.name === "link"
        )?.value;

        if (url) {
          validateUrl(url, node, file);
        }
      }
    }
  );
};

const processor = remark()
  .use(remarkFrontmatter)
  .use(remarkMdx)
  .use(remarkPluginValidateLinks);

async function main() {
  console.log("🔎 Checking for broken links...");

  const files = readdirp("docs", {
    fileFilter: "*.mdx",
    type: "files",
  });

  const checkedFiles = [];

  for await (const file of files) {
    const contents = await fs.promises.readFile(file.fullPath, "utf8");
    const result = await processor.process({
      path: file.path,
      value: contents,
    });

    if (result.messages.length > 0) {
      checkedFiles.push(result);
    }
  }

  const output = reporter(checkedFiles, { quiet: true });

  if (output) {
    console.log(output);
    process.exitCode = 1;
  } else {
    console.log("✅ No broken links found!");
  }
}

main();