fix(build): preserve environment key ordering when user defines vite.environments.ssr (#17760)

Author: factory[bot]

.changeset/witty-cloths-do.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes a build failure when defining `vite.environments.ssr` in the Astro config. User-provided environment config for `ssr`, `prerender`, or `client` is now properly deep-merged with Astro's internal environment settings instead of silently breaking the server entry naming.

packages/astro/src/core/build/vite-build-config.ts

@@ -50,6 +50,21 @@ export function createViteBuildConfig(opts: CreateViteBuildConfigOptions): vite.
 	const { settings, viteConfig, routes, plugins, builder, isRolldownInput } = opts;
 	const legacyAdapter = !settings.adapter || isLegacyAdapter(settings.adapter);
 
+	// Separate Astro-managed environment keys from user-defined ones so that the
+	// managed environments always appear last (and in a fixed order) in the object.
+	// Vite's `configResolved` fires per environment in key-insertion order, and the
+	// `astro:resolve-input` plugin relies on `ssr` being resolved last so its
+	// rolldown input value is the one that persists. If a user-defined
+	// `environments.ssr` is spread first, its key position would place SSR earlier
+	// in the iteration order, causing later environments to overwrite the saved
+	// input. See https://github.com/withastro/astro/issues/17760
+	const {
+		[ASTRO_VITE_ENVIRONMENT_NAMES.ssr]: userSsr,
+		[ASTRO_VITE_ENVIRONMENT_NAMES.prerender]: userPrerender,
+		[ASTRO_VITE_ENVIRONMENT_NAMES.client]: userClient,
+		...userEnvironments
+	} = viteConfig.environments ?? {};
+
 	return {
 		...viteConfig,
 		logLevel: viteConfig.logLevel ?? 'error',
@@ -143,8 +158,9 @@ export function createViteBuildConfig(opts: CreateViteBuildConfigOptions): vite.
 		envPrefix: viteConfig.envPrefix ?? 'PUBLIC_',
 		base: settings.config.base,
 		environments: {
-			...(viteConfig.environments ?? {}),
+			...userEnvironments,
 			[ASTRO_VITE_ENVIRONMENT_NAMES.prerender]: {
+				...userPrerender,
 				build: {
 					emitAssets: true,
 					outDir: fileURLToPath(getPrerenderOutputDirectory(settings)),
@@ -157,24 +173,21 @@ export function createViteBuildConfig(opts: CreateViteBuildConfigOptions): vite.
 						output: {
 							entryFileNames: `${PRERENDER_ENTRY_FILENAME_PREFIX}.[hash].mjs`,
 							format: 'esm',
-							...viteConfig.environments?.prerender?.build?.rolldownOptions?.output,
+							...userPrerender?.build?.rolldownOptions?.output,
 						},
 					},
 					ssr: true,
 				},
 			},
 			[ASTRO_VITE_ENVIRONMENT_NAMES.client]: {
+				...userClient,
 				build: {
 					emitAssets: true,
 					target: 'esnext',
 					outDir: fileURLToPath(getClientOutputDirectory(settings)),
 					copyPublicDir: true,
-					sourcemap:
-						viteConfig.environments?.client?.build?.sourcemap ??
-						viteConfig.build?.sourcemap ??
-						false,
-					minify:
-						viteConfig.environments?.client?.build?.minify ?? viteConfig.build?.minify ?? true,
+					sourcemap: userClient?.build?.sourcemap ?? viteConfig.build?.sourcemap ?? false,
+					minify: userClient?.build?.minify ?? viteConfig.build?.minify ?? true,
 					rolldownOptions: {
 						preserveEntrySignatures: 'exports-only',
 						output: {
@@ -199,17 +212,18 @@ export function createViteBuildConfig(opts: CreateViteBuildConfigOptions): vite.
 								}
 								return `${settings.config.build.assets}/[name].[hash][extname]`;
 							},
-							...viteConfig.environments?.client?.build?.rolldownOptions?.output,
+							...userClient?.build?.rolldownOptions?.output,
 						},
 					},
 				},
 			},
 			[ASTRO_VITE_ENVIRONMENT_NAMES.ssr]: {
+				...userSsr,
 				build: {
 					outDir: fileURLToPath(getServerOutputDirectory(settings)),
 					rolldownOptions: {
 						output: {
-							...viteConfig.environments?.ssr?.build?.rolldownOptions?.output,
+							...userSsr?.build?.rolldownOptions?.output,
 						},
 					},
 				},

packages/astro/test/units/build/vite-build-config.test.ts

@@ -246,6 +246,95 @@ describe('createViteBuildConfig', () => {
 		});
 	});
 
+	describe('environment key ordering', () => {
+		it('places ssr environment last even when user defines environments.ssr', async () => {
+			const settings = await createBasicSettings();
+			const config = buildConfig({
+				settings,
+				viteConfig: {
+					environments: {
+						ssr: {
+							resolve: { external: ['some-pkg'] },
+						},
+					},
+				},
+			});
+
+			const envKeys = Object.keys(config.environments ?? {});
+			assert.equal(envKeys.at(-1), 'ssr', 'ssr must be the last environment key');
+		});
+
+		it('preserves user non-build properties on the ssr environment', async () => {
+			const settings = await createBasicSettings();
+			const config = buildConfig({
+				settings,
+				viteConfig: {
+					environments: {
+						ssr: {
+							resolve: { external: ['some-pkg'] },
+						},
+					},
+				},
+			});
+
+			const ssrEnv = config.environments?.ssr as Record<string, any>;
+			assert.deepEqual(ssrEnv.resolve, { external: ['some-pkg'] });
+		});
+
+		it('preserves user non-build properties on the prerender environment', async () => {
+			const settings = await createBasicSettings();
+			const config = buildConfig({
+				settings,
+				viteConfig: {
+					environments: {
+						prerender: {
+							resolve: { external: ['some-pkg'] },
+						},
+					},
+				},
+			});
+
+			const prerenderEnv = config.environments?.prerender as Record<string, any>;
+			assert.deepEqual(prerenderEnv.resolve, { external: ['some-pkg'] });
+		});
+
+		it('preserves user non-build properties on the client environment', async () => {
+			const settings = await createBasicSettings();
+			const config = buildConfig({
+				settings,
+				viteConfig: {
+					environments: {
+						client: {
+							resolve: { external: ['some-pkg'] },
+						},
+					},
+				},
+			});
+
+			const clientEnv = config.environments?.client as Record<string, any>;
+			assert.deepEqual(clientEnv.resolve, { external: ['some-pkg'] });
+		});
+
+		it('does not include managed keys when user sets environments.ssr before other keys', async () => {
+			const settings = await createBasicSettings();
+			const config = buildConfig({
+				settings,
+				viteConfig: {
+					environments: {
+						ssr: { resolve: { external: ['a'] } },
+						prerender: { resolve: { external: ['b'] } },
+						client: { resolve: { external: ['c'] } },
+					},
+				},
+			});
+
+			const envKeys = Object.keys(config.environments ?? {});
+			// Managed keys appear exactly once each, at the end
+			const lastThree = envKeys.slice(-3);
+			assert.deepEqual(lastThree, ['prerender', 'client', 'ssr']);
+		});
+	});
+
 	describe('general config', () => {
 		it('sets base from settings config', async () => {
 			const settings = await createBasicSettings({ base: '/blog' });