md025.mjs

// @ts-check

import { addErrorContext, frontMatterHasTitle } from "../helpers/helpers.cjs";
import { getHeadingLevel, getHeadingText } from "../helpers/micromark-helpers.cjs";
import { filterByTypesCached } from "./cache.mjs";

/** @type {import("markdownlint").Rule} */
export default {
  "names": [ "MD025", "single-title", "single-h1" ],
  "description": "Multiple top-level headings in the same document",
  "tags": [ "headings" ],
  "parser": "micromark",
  "function": function MD025(params, onError) {
    const level = Number(params.config.level || 1);
    const foundFrontMatterTitle =
      frontMatterHasTitle(
        params.frontMatterLines,
        params.config.front_matter_title
      );
    let hasTopLevelHeading = false;
    for (const heading of filterByTypesCached([ "atxHeading", "setextHeading" ])) {
      const headingLevel = getHeadingLevel(heading);
      if (headingLevel === level) {
        if (hasTopLevelHeading || foundFrontMatterTitle) {
          const headingText = getHeadingText(heading);
          addErrorContext(
            onError,
            heading.startLine,
            headingText
          );
        } else if (heading.startLine === 1) {
          hasTopLevelHeading = true;
        }
      }
    }
  }
};