feat: html anchor support

src/index.js

@@ -7,6 +7,7 @@ const {
   filterTokens,
   convertHeadingToHTMLFragment,
   getMarkdownHeadings,
+  getMarkdownAnchorHTMLFragments,
 } = require("./utils.js")
 
 /** @typedef {import('markdownlint').Rule} MarkdownLintRule */
@@ -63,6 +64,8 @@ const customRule = {
             if (type === "link_open" && url.hash !== "") {
               const fileContent = fs.readFileSync(url, { encoding: "utf8" })
               const headings = getMarkdownHeadings(fileContent)
+              const anchorHTMLFragments =
+                getMarkdownAnchorHTMLFragments(fileContent)
 
               /** @type {Map<string, number>} */
               const fragments = new Map()
@@ -77,6 +80,8 @@ const customRule = {
                 return fragment
               })
 
+              headingsHTMLFragments.push(...anchorHTMLFragments)
+
               if (!headingsHTMLFragments.includes(url.hash)) {
                 onError({
                   lineNumber,

src/utils.js

@@ -1,4 +1,6 @@
 const MarkdownIt = require("markdown-it")
+// @ts-ignore
+const { getHtmlAttributeRe } = require("markdownlint-rule-helpers")
 
 /** @typedef {import('markdownlint').RuleParams} MarkdownLintRuleParams */
 /** @typedef {import('markdownlint').MarkdownItToken} MarkdownItToken */
@@ -94,8 +96,55 @@ const getMarkdownHeadings = (content) => {
   return headings
 }
 
+const anchorNameRe = getHtmlAttributeRe("name")
+const anchorIdRe = getHtmlAttributeRe("id")
+
+/**
+ * Gets the anchor HTML fragments from a Markdown string.
+ * @param {string} content
+ * @returns {string[]}
+ */
+const getMarkdownAnchorHTMLFragments = (content) => {
+  const markdownIt = new MarkdownIt({ html: true })
+  const tokens = markdownIt.parse(content, {})
+
+  /** @type {string[]} */
+  const result = []
+
+  for (const token of tokens) {
+    if (token.type === "inline") {
+      if (!token.children) {
+        continue
+      }
+
+      for (const child of token.children) {
+        if (child.type === "html_inline") {
+          const anchorMatch =
+            anchorIdRe.exec(token.content) || anchorNameRe.exec(token.content)
+          if (!anchorMatch || anchorMatch.length === 0) {
+            continue
+          }
+
+          const anchorIdOrName = anchorMatch[1]
+          if (anchorMatch[1] === undefined) {
+            continue
+          }
+
+          const anchorHTMLFragment = "#" + anchorIdOrName
+          if (!result.includes(anchorHTMLFragment)) {
+            result.push(anchorHTMLFragment)
+          }
+        }
+      }
+    }
+  }
+
+  return result
+}
+
 module.exports = {
   filterTokens,
   convertHeadingToHTMLFragment,
   getMarkdownHeadings,
+  getMarkdownAnchorHTMLFragments,
 }