Fix image metadata validation in StarlightPage schema (#3118)

3 files changed, 110 insertions, 21 deletions

diff --git a/.changeset/warm-adults-wash.md b/.changeset/warm-adults-wash.md
new file mode 100644
index 00000000..15bf8ddb
--- /dev/null
+++ b/.changeset/warm-adults-wash.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/starlight': patch
+---
+
+Fixes passing imported SVGs to the `frontmatter` prop of the `<StarlightPage>` component in Astro ≥5.7.0
diff --git a/packages/starlight/__tests__/basics/starlight-page-route-data.test.ts b/packages/starlight/__tests__/basics/starlight-page-route-data.test.ts
index 950eeab4..2c5f5363 100644
--- a/packages/starlight/__tests__/basics/starlight-page-route-data.test.ts
+++ b/packages/starlight/__tests__/basics/starlight-page-route-data.test.ts
@@ -1,11 +1,12 @@
+import type { ImageMetadata } from 'astro';
 import { expect, test, vi } from 'vitest';
-import { getRouteDataTestContext } from '../test-utils';
-import { generateRouteData } from '../../utils/routing/data';
 import { routes } from '../../utils/routing';
+import { generateRouteData } from '../../utils/routing/data';
 import {
 	generateStarlightPageRouteData,
 	type StarlightPageProps,
 } from '../../utils/starlight-page';
+import { getRouteDataTestContext } from '../test-utils';
 
 vi.mock('virtual:starlight/collection-config', async () =>
 	(await import('../test-utils')).mockedCollectionConfig()
@@ -523,3 +524,89 @@ test('generates data with a similar root shape to regular route data', async ()
 
 	expect(Object.keys(data).sort()).toEqual(Object.keys(starlightPageData).sort());
 });
+
+test('parses an ImageMetadata object successfully', async () => {
+	const fakeImportedImage: ImageMetadata = {
+		src: '/image-src.png',
+		width: 100,
+		height: 100,
+		format: 'png',
+	};
+	const data = await generateStarlightPageRouteData({
+		props: {
+			...starlightPageProps,
+			frontmatter: {
+				...starlightPageProps.frontmatter,
+				hero: {
+					image: { file: fakeImportedImage },
+				},
+			},
+		},
+		context: getRouteDataTestContext(starlightPagePathname),
+	});
+	expect(data.entry.data.hero?.image).toBeDefined();
+	// @ts-expect-error — image’s type can be different shapes but we know it’s this one here
+	expect(data.entry.data.hero?.image!['file']).toMatchInlineSnapshot(`
+		{
+		  "format": "png",
+		  "height": 100,
+		  "src": "/image-src.png",
+		  "width": 100,
+		}
+	`);
+});
+
+test('parses an image that is also a function successfully', async () => {
+	const fakeImportedSvg = (() => {}) as unknown as ImageMetadata;
+	Object.assign(fakeImportedSvg, { src: '/image-src.svg', width: 100, height: 100, format: 'svg' });
+	const data = await generateStarlightPageRouteData({
+		props: {
+			...starlightPageProps,
+			frontmatter: {
+				...starlightPageProps.frontmatter,
+				hero: {
+					image: { file: fakeImportedSvg },
+				},
+			},
+		},
+		context: getRouteDataTestContext(starlightPagePathname),
+	});
+	expect(data.entry.data.hero?.image).toBeDefined();
+	// @ts-expect-error — image’s type can be different shapes but we know it’s this one here
+	expect(data.entry.data.hero?.image!['file']).toMatchInlineSnapshot(`[Function]`);
+	// @ts-expect-error
+	expect(data.entry.data.hero?.image!['file']).toHaveProperty('src');
+	// @ts-expect-error
+	expect(data.entry.data.hero?.image!['file']).toHaveProperty('width');
+	// @ts-expect-error
+	expect(data.entry.data.hero?.image!['file']).toHaveProperty('height');
+	// @ts-expect-error
+	expect(data.entry.data.hero?.image!['file']).toHaveProperty('format');
+});
+
+test('fails to parse an image without the expected metadata properties', async () => {
+	await expect(() =>
+		generateStarlightPageRouteData({
+			props: {
+				...starlightPageProps,
+				frontmatter: {
+					...starlightPageProps.frontmatter,
+					hero: {
+						image: {
+							// @ts-expect-error intentionally incorrect input
+							file: () => {},
+						},
+					},
+				},
+			},
+			context: getRouteDataTestContext(starlightPagePathname),
+		})
+	).rejects.toThrowErrorMatchingInlineSnapshot(`
+		"[AstroUserError]:
+			Invalid frontmatter props passed to the \`<StarlightPage/>\` component.
+		Hint:
+			**hero.image**: Did not match union.
+			> Expected type \`file | { dark; light } | { html: string }\`
+			> Received \`{}\`"
+	`);
+});
diff --git a/packages/starlight/utils/starlight-page.ts b/packages/starlight/utils/starlight-page.ts
index 7a297bf3..01fe7dd7 100644
--- a/packages/starlight/utils/starlight-page.ts
+++ b/packages/starlight/utils/starlight-page.ts
@@ -1,5 +1,5 @@
 import { z } from 'astro/zod';
-import { type ContentConfig, type SchemaContext } from 'astro:content';
+import { type ContentConfig, type ImageFunction, type SchemaContext } from 'astro:content';
 import project from 'virtual:starlight/project-context';
 import config from 'virtual:starlight/user-config';
 import { getCollectionPathFromRoot } from './collection';
@@ -179,25 +179,22 @@ export async function generateStarlightPageRouteData({
 
 /** Validates the Starlight page frontmatter properties from the props received by a Starlight page. */
 async function getStarlightPageFrontmatter(frontmatter: StarlightPageFrontmatter) {
-	// This needs to be in sync with ImageMetadata.
-	// https://github.com/withastro/astro/blob/cf993bc263b58502096f00d383266cd179f331af/packages/astro/src/assets/types.ts#L32
 	const schema = await StarlightPageFrontmatterSchema({
-		image: () =>
-			z.object({
-				src: z.string(),
-				width: z.number(),
-				height: z.number(),
-				format: z.union([
-					z.literal('png'),
-					z.literal('jpg'),
-					z.literal('jpeg'),
-					z.literal('tiff'),
-					z.literal('webp'),
-					z.literal('gif'),
-					z.literal('svg'),
-					z.literal('avif'),
-				]),
-			}),
+		image: (() =>
+			// Mock validator for ImageMetadata.
+			// https://github.com/withastro/astro/blob/cf993bc263b58502096f00d383266cd179f331af/packages/astro/src/assets/types.ts#L32
+			// It uses a custom validation approach because imported SVGs have a type of `function` as
+			// well as containing the metadata properties and this ensures we handle those correctly.
+			z.custom(
+				(value) =>
+					value &&
+					(typeof value === 'function' || typeof value === 'object') &&
+					'src' in value &&
+					'width' in value &&
+					'height' in value &&
+					'format' in value,
+				'Invalid image passed to `<StarlightPage>` component. Expected imported `ImageMetadata` object.'
+			)) as ImageFunction,
 	});
 
 	// Starting with Astro 4.14.0, a frontmatter schema that contains collection references will