Fix `sidebar` frontmatter use in internal links (#2613)

Co-authored-by: HiDeoo <494699+HiDeoo@users.noreply.github.com>

3 files changed, 30 insertions, 8 deletions

diff --git a/.changeset/wild-donkeys-join.md b/.changeset/wild-donkeys-join.md
new file mode 100644
index 00000000..573e1de2
--- /dev/null
+++ b/.changeset/wild-donkeys-join.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/starlight': patch
+---
+
+Fixes support for `sidebar` frontmatter options in sidebar entries using `slug` or the string shorthand for internal links
diff --git a/packages/starlight/__tests__/i18n-sidebar/i18n-sidebar.test.ts b/packages/starlight/__tests__/i18n-sidebar/i18n-sidebar.test.ts
index 341a20ed..ee62e268 100644
--- a/packages/starlight/__tests__/i18n-sidebar/i18n-sidebar.test.ts
+++ b/packages/starlight/__tests__/i18n-sidebar/i18n-sidebar.test.ts
@@ -12,7 +12,13 @@ vi.mock('astro:content', async () =>
 			['fr/manual-setup.mdx', { title: 'Installation manuelle' }],
 			['environmental-impact.md', { title: 'Eco-friendly docs' }],
 			['fr/environmental-impact.md', { title: 'Documents écologiques' }],
-			['guides/pages.mdx', { title: 'Pages' }],
+			[
+				'guides/pages.mdx',
+				{
+					title: 'Pages',
+					sidebar: { label: 'Pages Guide', badge: 'Test', attrs: { class: 'test' } },
+				},
+			],
 			['fr/guides/pages.mdx', { title: 'Pages' }],
 			['guides/authoring-content.mdx', { title: 'Authoring Content in Markdown' }],
 			['fr/guides/authoring-content.mdx', { title: 'Création de contenu en Markdown' }],
@@ -69,11 +75,16 @@ describe('getSidebar', () => {
 			    "collapsed": false,
 			    "entries": [
 			      {
-			        "attrs": {},
-			        "badge": undefined,
+			        "attrs": {
+			          "class": "test",
+			        },
+			        "badge": {
+			          "text": "Test",
+			          "variant": "default",
+			        },
 			        "href": "/guides/pages",
 			        "isCurrent": false,
-			        "label": "Pages",
+			        "label": "Pages Guide",
 			        "type": "link",
 			      },
 			      {
diff --git a/packages/starlight/utils/navigation.ts b/packages/starlight/utils/navigation.ts
index 1e474476..f9dffff1 100644
--- a/packages/starlight/utils/navigation.ts
+++ b/packages/starlight/utils/navigation.ts
@@ -142,8 +142,8 @@ function linkFromInternalSidebarLinkItem(
 	// Astro passes root `index.[md|mdx]` entries with a slug of `index`
 	const slug = item.slug === 'index' ? '' : item.slug;
 	const localizedSlug = locale ? (slug ? locale + '/' + slug : locale) : slug;
-	const entry = routes.find((entry) => localizedSlug === entry.slug);
-	if (!entry) {
+	const route = routes.find((entry) => localizedSlug === entry.slug);
+	if (!route) {
 		const hasExternalSlashes = item.slug.at(0) === '/' || item.slug.at(-1) === '/';
 		if (hasExternalSlashes) {
 			throw new AstroError(
@@ -158,9 +158,15 @@ function linkFromInternalSidebarLinkItem(
 			);
 		}
 	}
+	const frontmatter = route.entry.data;
 	const label =
-		pickLang(item.translations, localeToLang(locale)) || item.label || entry.entry.data.title;
-	return makeSidebarLink(entry.slug, label, getSidebarBadge(item.badge, locale, label), item.attrs);
+		pickLang(item.translations, localeToLang(locale)) ||
+		item.label ||
+		frontmatter.sidebar?.label ||
+		frontmatter.title;
+	const badge = item.badge ?? frontmatter.sidebar?.badge;
+	const attrs = { ...frontmatter.sidebar?.attrs, ...item.attrs };
+	return makeSidebarLink(route.slug, label, getSidebarBadge(badge, locale, label), attrs);
 }
 
 /** Process sidebar link options to create a link entry. */