markdownlint/lib/md051.js

// @ts-check

"use strict";

const { addError, escapeForRegExp, filterTokens, forEachInlineChild,
  forEachHeading, htmlElementRe } = require("../helpers");

// Regular expression for identifying HTML anchor names
const identifierRe = /(?:id|name)\s*=\s*['"]?([^'"\s>]+)/iu;

/**
 * Converts a Markdown heading into an HTML fragment according to the rules
 * used by GitHub.
 *
 * @param {Object} inline Inline token for heading.
 * @returns {string} Fragment string for heading.
 */
function convertHeadingToHTMLFragment(inline) {
  const inlineText = inline.children.map((token) => token.content).join("");
  return "#" + encodeURIComponent(
    inlineText
      .toLowerCase()
      // RegExp source with Ruby's \p{Word} expanded into its General Categories
      // eslint-disable-next-line max-len
      // https://github.com/gjtorikian/html-pipeline/blob/main/lib/html/pipeline/toc_filter.rb
      // https://ruby-doc.org/core-3.0.2/Regexp.html
      .replace(
        /[^\p{Letter}\p{Mark}\p{Number}\p{Connector_Punctuation}\- ]/gu,
        ""
      )
      .replace(/ /gu, "-")
  );
}

module.exports = {
  "names": [ "MD051", "link-fragments" ],
  "description": "Link fragments should be valid",
  "tags": [ "links" ],
  "function": function MD051(params, onError) {
    const fragments = new Map();
    // Process headings
    forEachHeading(params, (heading, content, inline) => {
      const fragment = convertHeadingToHTMLFragment(inline);
      const count = fragments.get(fragment) || 0;
      if (count) {
        fragments.set(`${fragment}-${count}`, 0);
      }
      fragments.set(fragment, count + 1);
    });
    // Process HTML anchors
    const processHtmlToken = (token) => {
      let match = null;
      while ((match = htmlElementRe.exec(token.content)) !== null) {
        const [ tag, , element ] = match;
        if (element.toLowerCase() === "a") {
          const idMatch = identifierRe.exec(tag);
          if (idMatch) {
            fragments.set(`#${idMatch[1]}`, 0);
          }
        }
      }
    };
    filterTokens(params, "html_block", processHtmlToken);
    forEachInlineChild(params, "html_inline", processHtmlToken);
    // Process link fragments
    forEachInlineChild(params, "link_open", (token) => {
      const { attrs, lineNumber, line } = token;
      const href = attrs.find((attr) => attr[0] === "href");
      const id = href && href[1];
      if (id && (id.length > 1) && (id[0] === "#") && !fragments.has(id)) {
        let context = id;
        let range = null;
        const match = line.match(
          new RegExp(`\\[.*?\\]\\(${escapeForRegExp(context)}\\)`)
        );
        if (match) {
          context = match[0];
          range = [ match.index + 1, match[0].length ];
        }
        addError(onError, lineNumber, null, context, range);
      }
    });
  }
};