feat(core): add merge for

Author: fuma-nama

packages/core/package.json

@@ -53,6 +53,7 @@
     "zod": "^4.4.3"
   },
   "devDependencies": {
+    "@fastify/deepmerge": "^3.2.1",
     "@tailwindcss/oxide": "^4.3.0",
     "@types/mdx": "^2.0.13",
     "@types/node": "^25.7.0",
@@ -82,5 +83,8 @@
     "@types/react": {
       "optional": true
     }
+  },
+  "inlinedDependencies": {
+    "@fastify/deepmerge": "3.2.1"
   }
 }

packages/core/src/config.ts

@@ -45,8 +45,7 @@ export interface Layouts<C extends ConfigContext = ConfigContext> {
   notFound: ComponentType<AppContext<C> & { lang?: string }>;
 
   /**
-   * Define default props for page layouts.
-   * This will also be ignored if you specify a custom page layout wtih the `render` option.
+   * Define default props for page layouts, will be merged with current props.
    */
   defaultProps?: (
     this: AppContext<C>,

packages/core/src/layouts/docs.tsx

@@ -2,6 +2,7 @@ import type { ConfigContext, Layouts } from "@/config";
 import {
   AppContext,
   getGitHubFileUrl,
+  mergeLayoutConfigs,
   renderPageMeta,
   TransformChildren,
   TransformChildrenSlot,
@@ -30,7 +31,7 @@ export interface DocsLayoutOptions<C extends ConfigContext = ConfigContext> {
     markdownUrl?: string;
     lastModified?: Date | null;
     body?: ReactNode;
-    layoutProps?: TransformChildren<Partial<DocsLayoutProps>>;
+    layoutProps?: Partial<TransformChildren<DocsLayoutProps>>;
     pageProps?: TransformChildren<DocsPageProps>;
   }>;
 }
@@ -83,23 +84,22 @@ export function createDocsLayout<C extends ConfigContext = ConfigContext>({
     if (!page) unstable_notFound();
 
     async function getLayoutProps(
-      overrides?: TransformChildren<Partial<DocsLayoutProps>>,
+      overrides?: Partial<TransformChildren<DocsLayoutProps>>,
     ): Promise<TransformChildren<DocsLayoutProps>> {
       const { name, git } = siteConfig;
+      const inherit = await layouts.defaultProps?.call(props, page!);
 
-      if (layouts.defaultProps) {
-        overrides ??= await layouts.defaultProps.call(props, page!);
-      }
-
-      return {
-        tree: source.getPageTree(lang),
-        githubUrl: git ? `https://github.com/${git.user}/${git.repo}` : undefined,
-        ...overrides,
-        nav: {
-          title: name,
-          ...overrides?.nav,
+      return mergeLayoutConfigs(
+        {
+          tree: source.getPageTree(lang),
+          githubUrl: git ? `https://github.com/${git.user}/${git.repo}` : undefined,
+          nav: {
+            title: name,
+          },
         },
-      };
+        inherit,
+        overrides,
+      );
     }
 
     const _raw = await render?.call(props, page);

packages/core/src/layouts/home.tsx

@@ -1,6 +1,7 @@
 import type { ConfigContext, Layouts } from "@/config";
 import {
   type AppContext,
+  mergeLayoutConfigs,
   renderPageMeta,
   TransformChildren,
   TransformChildrenSlot,
@@ -62,19 +63,18 @@ export function createHomeLayout<C extends ConfigContext = ConfigContext>({
       overrides?: TransformChildren<HomeLayoutProps>,
     ): Promise<TransformChildren<HomeLayoutProps>> {
       const { name, git } = siteConfig;
+      const inherit = await layouts.defaultProps?.call(props, page!);
 
-      if (layouts.defaultProps) {
-        overrides ??= await layouts.defaultProps.call(props, page!);
-      }
-
-      return {
-        githubUrl: git ? `https://github.com/${git.user}/${git.repo}` : undefined,
-        ...overrides,
-        nav: {
-          title: name,
-          ...overrides?.nav,
+      return mergeLayoutConfigs(
+        {
+          githubUrl: git ? `https://github.com/${git.user}/${git.repo}` : undefined,
+          nav: {
+            title: name,
+          },
         },
-      };
+        inherit,
+        overrides,
+      );
     }
 
     const _raw = await render?.call(props, page);

packages/core/src/layouts/notebook.tsx

@@ -2,6 +2,7 @@ import type { ConfigContext, Layouts } from "@/config";
 import {
   AppContext,
   getGitHubFileUrl,
+  mergeLayoutConfigs,
   renderPageMeta,
   TransformChildren,
   TransformChildrenSlot,
@@ -30,7 +31,7 @@ export interface NotebookLayoutOptions<C extends ConfigContext = ConfigContext>
     markdownUrl?: string;
     lastModified?: Date | null;
     body?: ReactNode;
-    layoutProps?: TransformChildren<Partial<DocsLayoutProps>>;
+    layoutProps?: Partial<TransformChildren<DocsLayoutProps>>;
     pageProps?: TransformChildren<DocsPageProps>;
   }>;
 }
@@ -83,23 +84,22 @@ export function createNotebookLayout<C extends ConfigContext = ConfigContext>({
     if (!page) unstable_notFound();
 
     async function getLayoutProps(
-      overrides?: TransformChildren<Partial<DocsLayoutProps>>,
+      overrides?: Partial<TransformChildren<DocsLayoutProps>>,
     ): Promise<TransformChildren<DocsLayoutProps>> {
       const { name, git } = siteConfig;
+      const inherit = await layouts.defaultProps?.call(props, page!);
 
-      if (layouts.defaultProps) {
-        overrides ??= await layouts.defaultProps.call(props, page!);
-      }
-
-      return {
-        tree: source.getPageTree(lang),
-        githubUrl: git ? `https://github.com/${git.user}/${git.repo}` : undefined,
-        ...overrides,
-        nav: {
-          title: name,
-          ...overrides?.nav,
+      return mergeLayoutConfigs(
+        {
+          tree: source.getPageTree(lang),
+          githubUrl: git ? `https://github.com/${git.user}/${git.repo}` : undefined,
+          nav: {
+            title: name,
+          },
         },
-      };
+        inherit,
+        overrides,
+      );
     }
 
     const _raw = await render?.call(props, page);

packages/core/src/lib/shared.tsx

@@ -4,11 +4,12 @@ import path from "node:path";
 import type { LoaderOutput, Page } from "fumadocs-core/source";
 import type { Awaitable, Adapter, ServerPlugin } from "./types";
 import type { DocsLayoutContextData } from "@/layouts/docs";
-import { ComponentType, Fragment, type ReactNode } from "react";
+import { type ComponentType, Fragment, type ReactNode } from "react";
 import type { HomeLayoutContextData } from "@/layouts/home";
 import { fumadocsMdx } from "@/adapters/mdx";
 import type { RootProviderProps } from "fumadocs-ui/provider/waku";
 import type { NotebookLayoutContextData } from "@/layouts/notebook";
+import createDeepmerge from "@fastify/deepmerge";
 
 export interface AppContext<C extends ConfigContext = ConfigContext> {
   mode: BuildMode;
@@ -130,3 +131,5 @@ export function TransformChildrenSlot<T>({
 
   return <Comp {...props}>{children}</Comp>;
 }
+
+export const mergeLayoutConfigs = createDeepmerge({ all: true, onlyDefinedProperties: true });

packages/core/tsdown.config.ts

@@ -21,7 +21,7 @@ export default defineConfig({
     },
   },
   deps: {
-    onlyBundle: [],
+    onlyBundle: ["@fastify/deepmerge"],
     neverBundle: [/^virtual:/, /^node:/],
   },
   async onSuccess() {