Initial implementation of MD051/valid-link-fragments (refs #253, closes #495).

lib/md051.js

@@ -0,0 +1,46 @@
+// @ts-check
+
+"use strict";
+
+const { addError, forEachHeading, filterTokens } = require("../helpers");
+
+/**
+ * Converts a Markdown heading into an HTML fragment
+ * according to the rules used by GitHub.
+ *
+ * @param {string} string The string to convert.
+ * @returns {string} The converted string.
+ */
+function convertHeadingToHTMLFragment(string) {
+  return "#" + string
+    .toLowerCase()
+    .replace(/ /g, "-")
+    .replace(/[^-_a-z0-9]/g, "");
+}
+
+module.exports = {
+  "names": [ "MD051", "valid-link-fragments" ],
+  "description": "Link fragments should be valid",
+  "tags": [ "links" ],
+  "function": function MD051(params, onError) {
+    const validLinkFragments = [];
+    forEachHeading(params, (_heading, content) => {
+      validLinkFragments.push(convertHeadingToHTMLFragment(content));
+    });
+    filterTokens(params, "inline", (token) => {
+      token.children.forEach((child) => {
+        const { lineNumber, type, attrs } = child;
+        if (type === "link_open") {
+          const href = attrs.find((attr) => attr[0] === "href");
+          if (href !== undefined &&
+              href[1].startsWith("#") &&
+              !validLinkFragments.includes(href[1])
+          ) {
+            const detail = "Link Fragment is invalid";
+            addError(onError, lineNumber, detail, href[1]);
+          }
+        }
+      });
+    });
+  }
+};