From e25d0805505db2f1116e99d38a488d5cb39ed426 Mon Sep 17 00:00:00 2001
From: Divyansh Singh <40380293+brc-dd@users.noreply.github.com>
Date: Tue, 18 Mar 2025 09:31:13 +0530
Subject: [PATCH] fix: normalize url fragments in internal links to correctly
 resolve to anchors (#4628)

closes #4605

- Normalizations aren't applied to raw html inside markdown or vue code.
- It is assumed `slugify(slugify(something)) === slugify(something)`
---
 src/node/markdown/markdown.ts     |  8 ++++++--
 src/node/markdown/plugins/link.ts | 22 +++++++++++++++-------
 2 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/src/node/markdown/markdown.ts b/src/node/markdown/markdown.ts
index fd6bf492..bb56e0cf 100644
--- a/src/node/markdown/markdown.ts
+++ b/src/node/markdown/markdown.ts
@@ -13,7 +13,7 @@ import {
 import { sfcPlugin, type SfcPluginOptions } from '@mdit-vue/plugin-sfc'
 import { titlePlugin } from '@mdit-vue/plugin-title'
 import { tocPlugin, type TocPluginOptions } from '@mdit-vue/plugin-toc'
-import { slugify } from '@mdit-vue/shared'
+import { slugify as defaultSlugify } from '@mdit-vue/shared'
 import type {
   LanguageInput,
   ShikiTransformer,
@@ -232,6 +232,8 @@ export async function createMarkdownRenderer(
     await options.preConfig(md)
   }
 
+  const slugify = options.anchor?.slugify ?? defaultSlugify
+
   // custom plugins
   md.use(componentPlugin, { ...options.component })
     .use(highlightLinePlugin)
@@ -242,7 +244,8 @@ export async function createMarkdownRenderer(
     .use(
       linkPlugin,
       { target: '_blank', rel: 'noreferrer', ...options.externalLinks },
-      base
+      base,
+      slugify
     )
     .use(lineNumberPlugin, options.lineNumbers)
 
@@ -317,6 +320,7 @@ export async function createMarkdownRenderer(
   } as SfcPluginOptions)
     .use(titlePlugin)
     .use(tocPlugin, {
+      slugify,
       ...options.toc
     } as TocPluginOptions)
 
diff --git a/src/node/markdown/plugins/link.ts b/src/node/markdown/plugins/link.ts
index 3e48843c..2fe2e1ac 100644
--- a/src/node/markdown/plugins/link.ts
+++ b/src/node/markdown/plugins/link.ts
@@ -16,7 +16,8 @@ const indexRE = /(^|.*\/)index.md(#?.*)$/i
 export const linkPlugin = (
   md: MarkdownItAsync,
   externalAttrs: Record<string, string>,
-  base: string
+  base: string,
+  slugify: (str: string) => string
 ) => {
   md.renderer.rules.link_open = (
     tokens,
@@ -27,9 +28,12 @@ export const linkPlugin = (
   ) => {
     const token = tokens[idx]
     const hrefIndex = token.attrIndex('href')
-    const targetIndex = token.attrIndex('target')
-    const downloadIndex = token.attrIndex('download')
-    if (hrefIndex >= 0 && targetIndex < 0 && downloadIndex < 0) {
+    if (
+      hrefIndex >= 0 &&
+      token.attrIndex('target') < 0 &&
+      token.attrIndex('download') < 0 &&
+      token.attrGet('class') !== 'header-anchor' // header anchors are already normalized
+    ) {
       const hrefAttr = token.attrs![hrefIndex]
       const url = hrefAttr[1]
       if (isExternal(url)) {
@@ -54,7 +58,7 @@ export const linkPlugin = (
         ) {
           normalizeHref(hrefAttr, env)
         } else if (url.startsWith('#')) {
-          hrefAttr[1] = decodeURI(hrefAttr[1])
+          hrefAttr[1] = decodeURI(normalizeHash(hrefAttr[1]))
         }
 
         // append base to internal (non-relative) urls
@@ -72,7 +76,7 @@ export const linkPlugin = (
     const indexMatch = url.match(indexRE)
     if (indexMatch) {
       const [, path, hash] = indexMatch
-      url = path + hash
+      url = path + normalizeHash(hash)
     } else {
       let cleanUrl = url.replace(/[?#].*$/, '')
       // transform foo.md -> foo[.html]
@@ -88,7 +92,7 @@ export const linkPlugin = (
         cleanUrl += '.html'
       }
       const parsed = new URL(url, 'http://a.com')
-      url = cleanUrl + parsed.search + parsed.hash
+      url = cleanUrl + parsed.search + normalizeHash(parsed.hash)
     }
 
     // ensure leading . for relative paths
@@ -103,6 +107,10 @@ export const linkPlugin = (
     hrefAttr[1] = decodeURI(url)
   }
 
+  function normalizeHash(str: string) {
+    return str ? encodeURI('#' + slugify(decodeURI(str).slice(1))) : ''
+  }
+
   function pushLink(link: string, env: MarkdownEnv) {
     const links = env.links || (env.links = [])
     links.push(link)