From f4cfe2f650c56fd9cf15ffefb827e5bd17d60ca3 Mon Sep 17 00:00:00 2001
From: Jonathan Doughty <jonathandoughty04@gmail.com>
Date: Sun, 31 May 2026 12:37:29 -0400
Subject: [PATCH] fix(config): merge markdown hooks when extending config

---
 __tests__/unit/node/config.test.ts | 42 ++++++++++++++++++++++++++++++
 src/node/config.ts                 | 33 +++++++++++++++++++++--
 2 files changed, 73 insertions(+), 2 deletions(-)
 create mode 100644 __tests__/unit/node/config.test.ts

diff --git a/__tests__/unit/node/config.test.ts b/__tests__/unit/node/config.test.ts
new file mode 100644
index 00000000..8e0849bd
--- /dev/null
+++ b/__tests__/unit/node/config.test.ts
@@ -0,0 +1,42 @@
+import { mergeConfig } from 'node/config'
+
+describe('node/config', () => {
+  test('composes markdown hooks when merging configs', async () => {
+    const calls: string[] = []
+    const md = {} as any
+
+    const merged = mergeConfig(
+      {
+        markdown: {
+          preConfig: () => {
+            calls.push('base-pre')
+          },
+          config: async () => {
+            calls.push('base')
+          },
+          externalLinks: { rel: 'noopener' }
+        }
+      },
+      {
+        markdown: {
+          preConfig: async () => {
+            calls.push('child-pre')
+          },
+          config: () => {
+            calls.push('child')
+          },
+          externalLinks: { target: '_blank' }
+        }
+      }
+    )
+
+    await merged.markdown?.preConfig?.(md)
+    await merged.markdown?.config?.(md)
+
+    expect(calls).toEqual(['base-pre', 'child-pre', 'base', 'child'])
+    expect(merged.markdown?.externalLinks).toEqual({
+      rel: 'noopener',
+      target: '_blank'
+    })
+  })
+})
diff --git a/src/node/config.ts b/src/node/config.ts
index bdcd00e1..cef2fdbd 100644
--- a/src/node/config.ts
+++ b/src/node/config.ts
@@ -289,9 +289,13 @@ async function resolveConfigExtends(
 }
 
 export function mergeConfig(a: UserConfig, b: UserConfig, isRoot = true) {
+  return mergeObjectConfig(a, b, isRoot)
+}
+
+function mergeObjectConfig<T extends object>(a: T, b: T, isRoot = true): T {
   const merged: Record<string, any> = { ...a }
   for (const key in b) {
-    const value = b[key as keyof UserConfig]
+    const value = b[key as keyof T] as any
     if (value == null) {
       continue
     }
@@ -303,16 +307,41 @@ export function mergeConfig(a: UserConfig, b: UserConfig, isRoot = true) {
     if (isObject(existing) && isObject(value)) {
       if (isRoot && key === 'vite') {
         merged[key] = mergeViteConfig(existing, value)
+      } else if (key === 'markdown') {
+        merged[key] = mergeMarkdownConfig(existing, value)
       } else {
-        merged[key] = mergeConfig(existing, value, false)
+        merged[key] = mergeObjectConfig(existing, value, false)
       }
       continue
     }
     merged[key] = value
   }
+  return merged as T
+}
+
+function mergeMarkdownConfig(
+  a: NonNullable<UserConfig['markdown']>,
+  b: NonNullable<UserConfig['markdown']>
+) {
+  const merged = mergeObjectConfig(a, b, false)
+  merged.preConfig = mergeConfigHooks(a.preConfig, b.preConfig)
+  merged.config = mergeConfigHooks(a.config, b.config)
   return merged
 }
 
+function mergeConfigHooks<T extends (...args: any[]) => Awaitable<void>>(
+  a: T | undefined,
+  b: T | undefined
+): T | undefined {
+  if (!a) return b
+  if (!b) return a
+
+  return (async (...args: Parameters<T>) => {
+    await a(...args)
+    await b(...args)
+  }) as unknown as T
+}
+
 export async function resolveSiteData(
   root: string,
   userConfig?: UserConfig,