[cli][next][build-utils] Variants (#10549)

Co-authored-by: Ethan Arrowood <ethan.arrowood@vercel.com>

.changeset/nervous-apricots-heal.md

@@ -0,0 +1,7 @@
+---
+'@vercel/build-utils': patch
+'@vercel/next': patch
+'vercel': patch
+---
+
+Internal variants

packages/build-utils/src/types.ts

@@ -434,6 +434,13 @@ export interface Cron {
   schedule: string;
 }
 
+// TODO: Proper description once complete
+export interface Flag {
+  key: string;
+  defaultValue?: unknown;
+  metadata: Record<string, unknown>;
+}
+
 /** The framework which created the function */
 export interface FunctionFramework {
   slug: string;
@@ -458,6 +465,7 @@ export interface BuildResultV2Typical {
   framework?: {
     version: string;
   };
+  flags?: Flag[];
 }
 
 export type BuildResultV2 = BuildResultV2Typical | BuildResultBuildOutput;

packages/cli/src/commands/build/index.ts

@@ -21,6 +21,7 @@ import {
   NowBuildError,
   Cron,
   validateNpmrc,
+  Flag,
 } from '@vercel/build-utils';
 import {
   detectBuilders,
@@ -93,6 +94,7 @@ interface BuildOutputConfig {
     version: string;
   };
   crons?: Cron[];
+  flags?: Flag[];
 }
 
 /**
@@ -627,6 +629,7 @@ async function doBuild(
   const mergedWildcard = mergeWildcard(buildResults.values());
   const mergedOverrides: Record<string, PathOverride> =
     overrides.length > 0 ? Object.assign({}, ...overrides) : undefined;
+  const mergedFlags = mergeFlags(buildResults.values());
 
   const framework = await getFramework(cwd, buildResults);
 
@@ -640,6 +643,7 @@ async function doBuild(
     overrides: mergedOverrides,
     framework,
     crons: mergedCrons,
+    flags: mergedFlags,
   };
   await fs.writeJSON(join(outputDir, 'config.json'), config, { spaces: 2 });
 
@@ -774,3 +778,15 @@ function mergeWildcard(
   }
   return wildcard;
 }
+
+function mergeFlags(
+  buildResults: Iterable<BuildResult | BuildOutputConfig>
+): BuildResultV2Typical['flags'] {
+  return Array.from(buildResults).flatMap(result => {
+    if ('flags' in result) {
+      return result.flags ?? [];
+    }
+
+    return [];
+  });
+}

packages/next/src/index.ts

@@ -76,6 +76,7 @@ import {
   getRoutesManifest,
   getSourceFilePathFromPage,
   getStaticFiles,
+  getVariantsManifest,
   isDynamicRoute,
   localizeDynamicRoutes,
   normalizeIndexOutput,
@@ -496,6 +497,11 @@ export const build: BuildV2 = async ({
     outputDirectory
   );
 
+  const variantsManifest = await getVariantsManifest(
+    entryPath,
+    outputDirectory
+  );
+
   const routesManifest = await getRoutesManifest(
     entryPath,
     outputDirectory,
@@ -1365,6 +1371,7 @@ export const build: BuildV2 = async ({
         privateOutputs,
         hasIsr404Page,
         hasIsr500Page,
+        variantsManifest,
       });
     }
 

packages/next/src/server-build.ts

@@ -12,6 +12,7 @@ import {
   debug,
   glob,
   Files,
+  Flag,
   BuildResultV2Typical as BuildResult,
 } from '@vercel/build-utils';
 import { Route, RouteWithHandle } from '@vercel/routing-utils';
@@ -45,6 +46,7 @@ import {
   UnwrapPromise,
   getOperationType,
   FunctionsConfigManifestV1,
+  VariantsManifest,
   RSC_CONTENT_TYPE,
   RSC_PREFETCH_SUFFIX,
 } from './utils';
@@ -111,6 +113,7 @@ export async function serverBuild({
   isCorrectLocaleAPIRoutes,
   lambdaCompressedByteLimit,
   requiredServerFilesManifest,
+  variantsManifest,
 }: {
   appPathRoutesManifest?: Record<string, string>;
   dynamicPages: string[];
@@ -151,6 +154,7 @@ export async function serverBuild({
   imagesManifest?: NextImagesManifest;
   prerenderManifest: NextPrerenderedRoutes;
   requiredServerFilesManifest: NextRequiredServerFilesManifest;
+  variantsManifest: VariantsManifest | null;
 }): Promise<BuildResult> {
   lambdaPages = Object.assign({}, lambdaPages, lambdaAppPaths);
 
@@ -1345,6 +1349,14 @@ export async function serverBuild({
     'RSC, Next-Router-State-Tree, Next-Router-Prefetch';
   const appNotFoundPath = path.posix.join('.', entryDirectory, '_not-found');
 
+  const flags: Flag[] = variantsManifest
+    ? Object.entries(variantsManifest).map(([key, value]) => ({
+        key,
+        ...value,
+        metadata: value.metadata ?? {},
+      }))
+    : [];
+
   return {
     wildcard: wildcardConfig,
     images: getImagesConfig(imagesManifest),
@@ -2046,5 +2058,6 @@ export async function serverBuild({
           ]),
     ],
     framework: { version: nextVersion },
+    flags,
   };
 }

packages/next/src/utils.ts

@@ -3025,3 +3025,35 @@ export function isApiPage(page: string | undefined) {
     .replace(/\\/g, '/')
     .match(/(serverless|server)\/pages\/api(\/|\.js$)/);
 }
+
+export type VariantsManifest = Record<
+  string,
+  {
+    defaultValue?: unknown;
+    metadata?: Record<string, unknown>;
+  }
+>;
+
+export async function getVariantsManifest(
+  entryPath: string,
+  outputDirectory: string
+): Promise<null | VariantsManifest> {
+  const pathVariantsManifest = path.join(
+    entryPath,
+    outputDirectory,
+    'variants-manifest.json'
+  );
+
+  const hasVariantsManifest = await fs
+    .access(pathVariantsManifest)
+    .then(() => true)
+    .catch(() => false);
+
+  if (!hasVariantsManifest) return null;
+
+  const variantsManifest: VariantsManifest = await fs.readJSON(
+    pathVariantsManifest
+  );
+
+  return variantsManifest;
+}