Fix autogenerated sidebar issue (#2688)

Co-authored-by: delucis <357379+delucis@users.noreply.github.com>

5 files changed, 62 insertions, 13 deletions

diff --git a/.changeset/wild-laws-play.md b/.changeset/wild-laws-play.md
new file mode 100644
index 00000000..d1d1ace2
--- /dev/null
+++ b/.changeset/wild-laws-play.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/starlight': patch
+---
+
+Fixes an issue with autogenerated sidebars when using Starlight with Astro's new Content Layer API where group names would be sluggified.
diff --git a/packages/starlight/__tests__/basics/navigation.test.ts b/packages/starlight/__tests__/basics/navigation.test.ts
index 90676507..0b4e5bd7 100644
--- a/packages/starlight/__tests__/basics/navigation.test.ts
+++ b/packages/starlight/__tests__/basics/navigation.test.ts
@@ -9,6 +9,7 @@ vi.mock('astro:content', async () =>
 			['guides/authoring-content.mdx', { title: 'Authoring Markdown' }],
 			['reference/frontmatter.md', { title: 'Frontmatter Reference', sidebar: { hidden: true } }],
 			['guides/project-structure.mdx', { title: 'Project Structure' }],
+			['Getting Started/intro.md', { title: 'Introduction' }],
 		],
 	})
 );
@@ -40,6 +41,22 @@ describe('getSidebar', () => {
 			      {
 			        "attrs": {},
 			        "badge": undefined,
+			        "href": "/getting-started/intro/",
+			        "isCurrent": false,
+			        "label": "Introduction",
+			        "type": "link",
+			      },
+			    ],
+			    "label": "Getting Started",
+			    "type": "group",
+			  },
+			  {
+			    "badge": undefined,
+			    "collapsed": false,
+			    "entries": [
+			      {
+			        "attrs": {},
+			        "badge": undefined,
 			        "href": "/guides/authoring-content/",
 			        "isCurrent": false,
 			        "label": "Authoring Markdown",
@@ -155,6 +172,14 @@ describe('flattenSidebar', () => {
 			  {
 			    "attrs": {},
 			    "badge": undefined,
+			    "href": "/getting-started/intro/",
+			    "isCurrent": false,
+			    "label": "Introduction",
+			    "type": "link",
+			  },
+			  {
+			    "attrs": {},
+			    "badge": undefined,
 			    "href": "/guides/authoring-content/",
 			    "isCurrent": false,
 			    "label": "Authoring Markdown",
@@ -182,9 +207,9 @@ describe('getPrevNextLinks', () => {
 			  "next": {
 			    "attrs": {},
 			    "badge": undefined,
-			    "href": "/guides/authoring-content/",
+			    "href": "/getting-started/intro/",
 			    "isCurrent": false,
-			    "label": "Authoring Markdown",
+			    "label": "Introduction",
 			    "type": "link",
 			  },
 			  "prev": {
diff --git a/packages/starlight/__tests__/test-utils.ts b/packages/starlight/__tests__/test-utils.ts
index 45dbde66..d6e3a711 100644
--- a/packages/starlight/__tests__/test-utils.ts
+++ b/packages/starlight/__tests__/test-utils.ts
@@ -28,7 +28,11 @@ function mockDoc(
 	data: z.input<typeof frontmatterSchema>,
 	body = ''
 ): StarlightDocsCollectionEntry {
-	const slug = docsFilePath.replace(/\.[^\.]+$/, '').replace(/\/index$/, '');
+	const slug = docsFilePath
+		.replace(/\.[^\.]+$/, '')
+		.replace(/\s/, '-')
+		.replace(/\/index$/, '')
+		.toLowerCase();
 
 	const doc: StarlightDocsCollectionEntry = {
 		id: project.legacyCollections ? docsFilePath : slug,
diff --git a/packages/starlight/utils/navigation.ts b/packages/starlight/utils/navigation.ts
index 76608601..921dc2fe 100644
--- a/packages/starlight/utils/navigation.ts
+++ b/packages/starlight/utils/navigation.ts
@@ -1,5 +1,6 @@
 import { AstroError } from 'astro/errors';
 import config from 'virtual:starlight/user-config';
+import project from 'virtual:starlight/project-context';
 import type { Badge, I18nBadge, I18nBadgeConfig } from '../schemas/badge';
 import type { PrevNextLinkConfig } from '../schemas/prevNextLink';
 import type {
@@ -14,8 +15,9 @@ import { formatPath } from './format-path';
 import { BuiltInDefaultLocale, pickLang } from './i18n';
 import { ensureLeadingSlash, ensureTrailingSlash, stripLeadingAndTrailingSlashes } from './path';
 import { getLocaleRoutes, routes, type Route } from './routing';
-import { localeToLang, slugToPathname } from './slugs';
+import { localeToLang, localizedId, slugToPathname } from './slugs';
 import type { StarlightConfig } from './user-config';
+import { getCollectionPathFromRoot } from './collection';
 
 const DirKey = Symbol('DirKey');
 const SlugKey = Symbol('SlugKey');
@@ -108,7 +110,7 @@ function groupFromAutogenerateConfig(
 			// Match against `foo/anything/else.md`.
 			doc.id.startsWith(localeDir + '/')
 	);
-	const tree = treeify(dirDocs, localeDir);
+	const tree = treeify(dirDocs, locale, localeDir);
 	const label = pickLang(item.translations, localeToLang(locale)) || item.label;
 	return {
 		type: 'group',
@@ -205,8 +207,8 @@ function pathsMatch(pathA: string, pathB: string) {
 function getBreadcrumbs(path: string, baseDir: string): string[] {
 	// Strip extension from path.
 	const pathWithoutExt = stripExtension(path);
-	// Index paths will match `baseDir` but we still need to consider them as a single segment.
-	if (pathWithoutExt === baseDir) return [path];
+	// Index paths will match `baseDir` and don’t include breadcrumbs.
+	if (pathWithoutExt === baseDir) return [];
 	// Ensure base directory ends in a trailing slash.
 	baseDir = ensureTrailingSlash(baseDir);
 	// Strip base directory from path if present.
@@ -218,16 +220,28 @@ function getBreadcrumbs(path: string, baseDir: string): string[] {
 }
 
 /** Turn a flat array of routes into a tree structure. */
-function treeify(routes: Route[], baseDir: string): Dir {
+function treeify(routes: Route[], locale: string | undefined, baseDir: string): Dir {
 	const treeRoot: Dir = makeDir(baseDir);
+	const collectionPathFromRoot = getCollectionPathFromRoot('docs', project);
 	routes
 		// Remove any entries that should be hidden
 		.filter((doc) => !doc.entry.data.sidebar.hidden)
+		// Compute the path of each entry from the root of the collection ahead of time.
+		.map(
+			(doc) =>
+				[
+					project.legacyCollections
+						? doc.id
+						: // For collections with a loader, use a localized filePath relative to the collection
+							localizedId(doc.entry.filePath.replace(`${collectionPathFromRoot}/`, ''), locale),
+					doc,
+				] as const
+		)
 		// Sort by depth, to build the tree depth first.
-		.sort((a, b) => b.id.split('/').length - a.id.split('/').length)
+		.sort(([a], [b]) => b.split('/').length - a.split('/').length)
 		// Build the tree
-		.forEach((doc) => {
-			const parts = getBreadcrumbs(doc.id, baseDir);
+		.forEach(([filePathFromContentDir, doc]) => {
+			const parts = getBreadcrumbs(filePathFromContentDir, baseDir);
 			let currentNode = treeRoot;
 
 			parts.forEach((part, index) => {
@@ -374,7 +388,7 @@ function getIntermediateSidebarFromConfig(
 	if (sidebarConfig) {
 		return sidebarConfig.map((group) => configItemToEntry(group, pathname, locale, routes));
 	} else {
-		const tree = treeify(routes, locale || '');
+		const tree = treeify(routes, locale, locale || '');
 		return sidebarFromDir(tree, pathname, locale, false);
 	}
 }
diff --git a/packages/starlight/utils/slugs.ts b/packages/starlight/utils/slugs.ts
index c811c550..c6b0b739 100644
--- a/packages/starlight/utils/slugs.ts
+++ b/packages/starlight/utils/slugs.ts
@@ -82,7 +82,8 @@ export function localizedSlug(slug: string, locale: string | undefined): string
 }
 
 /**
- * Convert a legacy collection entry ID to a different locale.
+ * Convert a legacy collection entry ID or filePath relative to the collection root to a different
+ * locale.
  * For example, passing an ID of `en/home.md` and a locale of `fr` results in `fr/home.md`.
  * An undefined locale is treated as the root locale, resulting in `home.md`.
  * @param id A collection entry ID