Convert markdownlint library to an ECMAScript module, replace markdownlint-micromark with micromark, stop publishing (large) markdownlint-browser.js, see https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c for guidance.

lib/md051.mjs

@@ -0,0 +1,164 @@
+// @ts-check
+
+import { addError, getHtmlAttributeRe } from "../helpers/helpers.cjs";
+import { filterByPredicate, filterByTypes, getHtmlTagInfo } from "../helpers/micromark-helpers.cjs";
+import { filterByTypesCached } from "./cache.mjs";
+
+// Regular expression for identifying HTML anchor names
+const idRe = getHtmlAttributeRe("id");
+const nameRe = getHtmlAttributeRe("name");
+const anchorRe = /\{(#[a-z\d]+(?:[-_][a-z\d]+)*)\}/gu;
+const lineFragmentRe = /^#(?:L\d+(?:C\d+)?-L\d+(?:C\d+)?|L\d+)$/;
+
+// Sets for filtering heading tokens during conversion
+const childrenExclude = new Set([ "image", "reference", "resource" ]);
+const tokensInclude = new Set(
+  [ "characterEscapeValue", "codeTextData", "data", "mathTextData" ]
+);
+
+/**
+ * Converts a Markdown heading into an HTML fragment according to the rules
+ * used by GitHub.
+ *
+ * @param {import("../helpers/micromark-helpers.cjs").Token} headingText Heading text token.
+ * @returns {string} Fragment string for heading.
+ */
+function convertHeadingToHTMLFragment(headingText) {
+  const inlineText =
+    filterByPredicate(
+      headingText.children,
+      (token) => tokensInclude.has(token.type),
+      (token) => (childrenExclude.has(token.type) ? [] : token.children)
+    )
+      .map((token) => token.text)
+      .join("");
+  return "#" + encodeURIComponent(
+    inlineText
+      .toLowerCase()
+      // RegExp source with Ruby's \p{Word} expanded into its General Categories
+      // 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, "-")
+  );
+}
+
+/**
+ * Unescapes the text of a String-type micromark Token.
+ *
+ * @param {import("../helpers/micromark-helpers.cjs").Token} token String-type micromark Token.
+ * @returns {string} Unescaped token text.
+ */
+function unescapeStringTokenText(token) {
+  return filterByTypes(token.children, [ "characterEscapeValue", "data" ])
+    .map((child) => child.text)
+    .join("");
+}
+
+/** @type {import("./markdownlint.mjs").Rule} */
+export default {
+  "names": [ "MD051", "link-fragments" ],
+  "description": "Link fragments should be valid",
+  "tags": [ "links" ],
+  "parser": "micromark",
+  "function": function MD051(params, onError) {
+    const ignoreCase = params.config.ignore_case || false;
+    const fragments = new Map();
+
+    // Process headings
+    const headingTexts = filterByTypesCached([ "atxHeadingText", "setextHeadingText" ]);
+    for (const headingText of headingTexts) {
+      const fragment = convertHeadingToHTMLFragment(headingText);
+      if (fragment !== "#") {
+        const count = fragments.get(fragment) || 0;
+        if (count) {
+          fragments.set(`${fragment}-${count}`, 0);
+        }
+        fragments.set(fragment, count + 1);
+        let match = null;
+        while ((match = anchorRe.exec(headingText.text)) !== null) {
+          const [ , anchor ] = match;
+          if (!fragments.has(anchor)) {
+            fragments.set(anchor, 1);
+          }
+        }
+      }
+    }
+
+    // Process HTML anchors
+    for (const token of filterByTypesCached([ "htmlText" ], true)) {
+      const htmlTagInfo = getHtmlTagInfo(token);
+      if (htmlTagInfo && !htmlTagInfo.close) {
+        const anchorMatch = idRe.exec(token.text) ||
+          (htmlTagInfo.name.toLowerCase() === "a" && nameRe.exec(token.text));
+        if (anchorMatch && anchorMatch.length > 0) {
+          fragments.set(`#${anchorMatch[1]}`, 0);
+        }
+      }
+    }
+
+    // Process link and definition fragments
+    /** @type {import("../helpers/micromark-helpers.cjs").TokenType[][]} */
+    const parentChilds = [
+      [ "link", "resourceDestinationString" ],
+      [ "definition", "definitionDestinationString" ]
+    ];
+    for (const [ parentType, definitionType ] of parentChilds) {
+      const links = filterByTypesCached([ parentType ]);
+      for (const link of links) {
+        const definitions = filterByTypes(link.children, [ definitionType ]);
+        for (const definition of definitions) {
+          const { endColumn, startColumn } = definition;
+          const text = unescapeStringTokenText(definition);
+          const encodedText = `#${encodeURIComponent(text.slice(1))}`;
+          if (
+            (text.length > 1) &&
+            text.startsWith("#") &&
+            !fragments.has(encodedText) &&
+            !lineFragmentRe.test(encodedText)
+          ) {
+            let context = undefined;
+            let range = undefined;
+            let fixInfo = undefined;
+            if (link.startLine === link.endLine) {
+              context = link.text;
+              range = [ link.startColumn, link.endColumn - link.startColumn ];
+              fixInfo = {
+                "editColumn": startColumn,
+                "deleteCount": endColumn - startColumn
+              };
+            }
+            const textLower = text.toLowerCase();
+            const mixedCaseKey = [ ...fragments.keys() ]
+              .find((key) => textLower === key.toLowerCase());
+            if (mixedCaseKey) {
+              // @ts-ignore
+              (fixInfo || {}).insertText = mixedCaseKey;
+              if (!ignoreCase && (mixedCaseKey !== text)) {
+                addError(
+                  onError,
+                  link.startLine,
+                  `Expected: ${mixedCaseKey}; Actual: ${text}`,
+                  context,
+                  range,
+                  fixInfo
+                );
+              }
+            } else {
+              addError(
+                onError,
+                link.startLine,
+                undefined,
+                context,
+                range
+              );
+            }
+          }
+        }
+      }
+    }
+  }
+};