[WIP] Move route data to Astro.locals

.changeset/chilled-bees-pump.md

@@ -0,0 +1,36 @@
+---
+'@astrojs/starlight': minor
+---
+
+Moves route data to `Astro.locals` instead of passing it down via component props
+
+⚠️ **Breaking change:**
+Previously, all of Starlight’s templating components, including user or plugin overrides, had access to a data object for the current route via `Astro.props`.
+This data is now available as `Astro.locals.starlightRoute` instead.
+
+To update, refactor any component overrides you have:
+
+- Remove imports of `@astrojs/starlight/props`, which are no longer required.
+- Update code that access `Astro.props` to use `Astro.locals.starlightRoute` instead.
+- Remove any spreading of `{...Astro.props}` into child components, which is no longer required.
+
+In the following example, a custom override for Starlight’s `LastUpdated` component is updated for the new style:
+
+```diff
+---
+import Default from '@astrojs/starlight/components/LastUpdated.astro';
+- import type { Props } from '@astrojs/starlight/props';
+
+- const { lastUpdated } = Astro.props;
++ const { lastUpdated } = Astro.locals.starlightRoute;
+
+const updatedThisYear = lastUpdated?.getFullYear() === new Date().getFullYear();
+---
+
+{updatedThisYear && (
+-   <Default {...Astro.props}><slot /></Default>
++   <Default><slot /></Default>
+)}
+```
+
+Any plugins you use that add component overrides will also need to be updated at the same time as updating Starlight.

docs/astro.config.mjs

@@ -35,6 +35,8 @@ export default defineConfig({
 	trailingSlash: 'always',
 	integrations: [
 		starlight({
+			// TODO(Chris): Remove the demo middleware
+			routeMiddleware: './src/demo-middleware.ts',
 			title: 'Starlight',
 			logo: {
 				light: '/src/assets/logo-light.svg',

docs/src/components/sidebar-preview.astro

@@ -6,7 +6,7 @@ import type {
 } from '../../../packages/starlight/schemas/sidebar';
 import SidebarSublist from '../../../packages/starlight/components/SidebarSublist.astro';
 import type { Badge } from '../../../packages/starlight/schemas/badge';
-import type { SidebarEntry } from '../../../packages/starlight/utils/navigation';
+import type { SidebarEntry } from '../../../packages/starlight/utils/routing/types';
 
 interface Props {
 	config: SidebarConfig;

docs/src/content/docs/guides/overriding-components.mdx

@@ -36,10 +36,11 @@ Overriding Starlight’s default components can be useful when:
    ```astro
    ---
    // src/components/EmailLink.astro
-   import type { Props } from '@astrojs/starlight/props';
+
+   const email = '[email protected]';
    ---
 
-   <a href="mailto:[email protected]">E-mail Me</a>
+   <a href=`mailto:${email}`>E-mail Me</a>
    ```
 
 3. Tell Starlight to use your custom component in the [`components`](/reference/configuration/#components) configuration option in `astro.config.mjs`:
@@ -70,52 +71,46 @@ You can build with Starlight’s default UI components just as you would with yo
 
 The example below shows a custom component that renders an e-mail link along with the default `SocialIcons` component:
 
-```astro {4,8}
+```astro {3,7}
 ---
 // src/components/EmailLink.astro
-import type { Props } from '@astrojs/starlight/props';
 import Default from '@astrojs/starlight/components/SocialIcons.astro';
 ---
 
 <a href="mailto:[email protected]">E-mail Me</a>
-<Default {...Astro.props}><slot /></Default>
+<Default><slot /></Default>
 ```
 
-When rendering a built-in component inside a custom component:
-
-- Spread `Astro.props` into it. This makes sure that it receives all the data it needs to render.
-- Add a [`<slot />`](https://docs.astro.build/en/basics/astro-components/#slots) inside the default component. This makes sure that if the component is passed any child elements, Astro knows where to render them.
+When rendering a built-in component inside a custom component add a [`<slot />`](https://docs.astro.build/en/basics/astro-components/#slots) inside the default component. This makes sure that if the component is passed any child elements, Astro knows where to render them.
 
 If you are reusing the [`PageFrame`](/reference/overrides/#pageframe) or [`TwoColumnContent`](/reference/overrides/#twocolumncontent) components which contain [named slots](https://docs.astro.build/en/basics/astro-components/#named-slots), you also need to [transfer](https://docs.astro.build/en/basics/astro-components/#transferring-slots) these slots as well.
 
 The example below shows a custom component that reuses the `TwoColumnContent` component which contains an additional `right-sidebar` named slot that needs to be transferred:
 
-```astro {9}
+```astro {8}
 ---
 // src/components/CustomContent.astro
-import type { Props } from '@astrojs/starlight/props';
 import Default from '@astrojs/starlight/components/TwoColumnContent.astro';
 ---
 
-<Default {...Astro.props}>
+<Default>
 	<slot />
 	<slot name="right-sidebar" slot="right-sidebar" />
 </Default>
 ```
 
 ## Use page data
 
-When overriding a Starlight component, your custom implementation receives a standard `Astro.props` object containing all the data for the current page.
+When overriding a Starlight component, you can access the global [`starlightRoute` object](/guides/route-data/) containing all the data for the current page.
 This allows you to use these values to control how your component template renders.
 
-For example, you can read the page’s frontmatter values as `Astro.props.entry.data`. In the following example, a replacement [`PageTitle`](/reference/overrides/#pagetitle) component uses this to display the current page’s title:
+In the following example, a replacement [`PageTitle`](/reference/overrides/#pagetitle) component displays the current page’s title as set in the content’s frontmatter:
 
-```astro {5} "{title}"
+```astro {4} "{title}"
 ---
 // src/components/Title.astro
-import type { Props } from '@astrojs/starlight/props';
 
-const { title } = Astro.props.entry.data;
+const { title } = Astro.locals.starlightRoute.entry.data;
 ---
 
 <h1 id="_top">{title}</h1>
@@ -127,28 +122,27 @@ const { title } = Astro.props.entry.data;
 </style>
 ```
 
-Learn more about all the available props in the [Overrides Reference](/reference/overrides/#component-props).
+Learn more about all the available properties in the [Route Data Reference](/reference/route-data/).
 
 ### Only override on specific pages
 
-Component overrides apply to all pages. However, you can conditionally render using values from `Astro.props` to determine when to show your custom UI, when to show Starlight’s default UI, or even when to show something entirely different.
+Component overrides apply to all pages. However, you can conditionally render using values from `starlightRoute` to determine when to show your custom UI, when to show Starlight’s default UI, or even when to show something entirely different.
 
 In the following example, a component overriding Starlight's [`Footer`](/reference/overrides/#footer-1) displays "Built with Starlight 🌟" on the homepage only, and otherwise shows the default footer on all other pages:
 
 ```astro
 ---
 // src/components/ConditionalFooter.astro
-import type { Props } from '@astrojs/starlight/props';
 import Default from '@astrojs/starlight/components/Footer.astro';
 
-const isHomepage = Astro.props.id === '';
+const isHomepage = Astro.locals.starlightRoute.id === '';
 ---
 
 {
 	isHomepage ? (
 		<footer>Built with Starlight 🌟</footer>
 	) : (
-		<Default {...Astro.props}>
+		<Default>
 			<slot />
 		</Default>
 	)

docs/src/content/docs/guides/route-data.mdx

@@ -0,0 +1,110 @@
+---
+title: Route Data
+description: Learn how Starlight’s page data model is used to render your pages and how you can customize it.
+---
+
+import { Steps } from '@astrojs/starlight/components';
+
+When Starlight renders a page in your documentation, it first creates a route data object to represent what is on that page.
+This guide explains how route data is generated, how it is used, and how you can customize it to modify Starlight’s default behavior.
+
+## What is route data?
+
+Starlight route data is an object constructed for each page of your site by combining the following parts of your project:
+
+1. The Starlight configuration in `astro.config.mjs`
+2. The content and frontmatter of the current page
+
+For example, route data includes a `siteTitle` property with a value based on the [`title`](/reference/configuration/#title-required) option in your Starlight configuration and a `toc` property generated from headings in the content for the current page.
+
+Some features can be configured both globally in the Starlight configuration and for a specific page in Markdown frontmatter.
+In this case, values set for a specific page in frontmatter override the global or default value.
+For example, route data includes a `pagination` object with links to the previous and next pages in the sidebar.
+If a page disables one of these, for example by setting `prev: false` in frontmatter, this will be reflected in the `pagination` object.
+
+See the [“Route Data Reference”](/reference/route-data/) for a full list of the available properties.
+
+## How is route data used?
+
+All of Starlight’s components have access to route data and use it to decide what to render for each page.
+For example, the `siteTitle` string is used to display the site title and the `sidebar` array is used to render the global sidebar navigation.
+
+Route data is available from the `Astro.locals.starlightRoute` global in Astro components:
+
+```astro title="example.astro"
+---
+const { siteTitle } = Astro.locals.starlightRoute;
+---
+
+<p>The title of this site is “{siteTitle}”</p>
+```
+
+If you are building [component overrides](/guides/overriding-components/), you can access route data like this to customize what you display.
+
+## Customizing route data
+
+Starlight’s route data works out of the box and does not require any configuration.
+However, for advanced use cases, you may want to customize route data for some or all pages to modify how your site displays.
+
+This is a similar concept to [component overrides](/guides/overriding-components/), but instead of modifying how Starlight renders your data, you modify the data Starlight renders.
+
+### When to customize route data
+
+Customizing route data can be useful when you want to modify how Starlight processes your data in a way not possible with existing configuration options.
+
+For example, you may want to filter sidebar items or customize titles for specific pages.
+Changes like this do not require modifying Starlight’s default components, only the data passed to those components.
+
+### How to customize route data
+
+You can customize route data using a special form of “middleware”.
+This is a function that is called every time Starlight renders a page and can modify values in the route data object.
+
+<Steps>
+
+1. Create a new file exporting an `onRequest` function using Starlight’s `defineRouteMiddleware()` utility:
+
+   ```ts
+   // src/routeData.ts
+   import { defineRouteMiddleware } from '@astrojs/starlight/route-data';
+
+   export const onRequest = defineRouteMiddleware(() => {});
+   ```
+
+2. Tell Starlight where your route data middleware file is located in `astro.config.mjs`:
+
+   ```js ins={9}
+   // astro.config.mjs
+   import { defineConfig } from 'astro/config';
+   import starlight from '@astrojs/starlight';
+
+   export default defineConfig({
+   	integrations: [
+   		starlight({
+   			title: 'My delightful docs site',
+   			routeMiddleware: './src/routeData.ts',
+   		}),
+   	],
+   });
+   ```
+
+3. Update your `onRequest` function to modify route data.
+
+   The first argument middleware receive is [Astro’s `context` object](https://docs.astro.build/en/reference/api-reference/).
+   This contains full information about the current page render, including the current URL and `locals`.
+
+   In this example, we are going to make our docs more exciting by adding an exclamation mark to the end of every page’s title.
+
+   ```ts
+   // src/routeData.ts
+   import { defineRouteMiddleware } from '@astrojs/starlight/route-data';
+
+   export const onRequest = defineRouteMiddleware((context) => {
+   	// Get the content collection entry for this page.
+   	const { entry } = context.locals.starlightRoute;
+   	// Update the title to add an exclamation mark.
+   	entry.data.title = entry.data.title + '!';
+   });
+   ```
+
+</Steps>