Flags SDK

#452 58e1f5b Thanks @luismeyer! - Replace @vercel/edge-config with @vercel/global-config.

Rename the Edge Config adapter package to @flags-sdk/global-config and rename repository-owned Edge Config files, exports, types, options, variables, and environment variables to Global Config.

The previous Edge Config names remain available as deprecated aliases, and the previous environment variables are still honored as fallbacks, so existing code keeps working without changes.

#434 4d6eb10 Thanks @dferber90! - Allow passing a NextRequest / Web Request directly to flag(req) and evaluate(flags, req) outside App Router (e.g. in routing middleware).

Previously only a Pages Router IncomingMessage, or a manually-flattened headers object, worked when calling a flag directly — passing a NextRequest produced empty headers because it wasn't recognized as already having a Headers instance.

#385 201f9d5 Thanks @dferber90! - When applications call evaluate() or precompute() function from flags/next it now defers bulk evaluation to the underlying adapters in case those support it, or otherwise falls back to evaluating each flag individually.

This speeds up evaluation for applications that need to evaluate multiple flags at once, as the runtime needs to handle fewer promises and more work is reused. In testing we have seen a 20x improvement when called with 100 flags.

import { evaluate } from "flags/next";
import { flagA, flagB } from "../flags";

// pass a list of flags
const [valueA, valueB] = await evaluate([flagA, flagB]);

// pass an object
const { a, b } = await evaluate({ a: flagA, b: flagB });

Adapters can opt into bulk evaluation by implementing a bulkDecide method and setting a stable adapterId. When both are present, flag evaluation groups flags that share the same adapterId and identify source and invokes bulkDecide once per group instead of calling decide per flag. Flags without a bulk-capable adapter still resolve through the normal per-flag path inside evaluate() and still benefit from now reusing the shared per-request headers, cookies, and overrides reads.

Tracing reflects this grouping. evaluate() (and therefore precompute()) now emits an evaluate span carrying a flagCount attribute. Within it, bulk-evaluated flags no longer emit an individual per-flag run span; instead each adapter group emits a single batch span (carrying the adapterId, the keys evaluated in the batch, and cachedCount/overrideCount/decidedCount attributes summarizing how the batch resolved) so per-flag instrumentation overhead is not reintroduced. Flags that fall back to the per-flag path continue to emit their own flag span as before.

c08f3e5: Improve performance by caching next/headers imports.

Previously every flag evaluation in Next.js App Router would run await import("next/headers"). The imported module is cached by the runtime, but we would still go through the event loop unnecessarily.

Now we cache the resolved module in a local variable so only the first call awaits the dynamic import; subsequent calls skip the microtask entirely.

c08f3e5: Reduce microtask queue overhead in flag evaluation by replacing the async IIFE around decide() with a direct call and Promise.resolve().

77727aa: The Flags SDK now handles when an app goes from precomputing one or more flags to precomputing none.

In this case we use __no_flags__ as the serialized value so the app will still rewrite and prerender the page.

precompute, generatePermutations, serialize and deserialize were adjusted to generate and parse __no_flags__ correctly.

795dfd4: Throw on declaration if flag is missing decide function.

When a feature flag is declared without a decide function, or with an adapter that is missing a decide function we will now throw an error at declaration time.