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Andrew Clark
94327e8ade
The test suite has accumulated a bunch of patterns for disabling tests
that are known to fail under some configuration: `it.skip`, `if
(isNextDev) { test('skipped in dev mode', () => {}); return }`, whole
describes toggled off by checking `process.env.__NEXT_CACHE_COMPONENTS`.
These all have the same flaw: nothing tells you when the thing you
skipped starts working. The test stays disabled forever, and the
workaround it was guarding rots along with it.
React solves this with the `@gate` pragma, and this PR ports it to the
Next.js e2e harness:
```ts
// Blocked on the optimization that marks a route as fully static when
// no dynamic params are referenced in Server Components.
// @gate !cacheComponents
it('navigates to a page with a lazily-generated static param', async () => {
// body unchanged
})
```
The test still runs. If the condition is false and the test fails, the
failure is absorbed and the suite stays green. If it _passes_, the suite
fails: the gate is stale, delete it. So instead of a skip that hides a
fixed bug indefinitely, you get a CI failure the day the fix lands.
When the condition is static, the inversion is Jest's own `test.failing`
under the hood. A lazy condition isn't known until the fixture's
resolved config is read inside the body, so those tests invert at
runtime instead.
`// @force-gate <condition>` skips for real — for tests that can't even
be attempted (prefetching is disabled in dev, deploy has no local build
output, the fixture won't build under the condition), and for tests of a
new API, where the disabled state can only throw and running it proves
nothing:
```ts
// Prefetching is disabled in dev, so this suite has nothing to test.
// @force-gate prefetching
describe('segment cache prefetch scheduling', () => {
// ...
})
```
There's no staleness check in that case, so this is a judgment call:
prefer `@gate` when the off state fails for a meaningful reason — the
flag changes behavior that already exists — and `@force-gate` when the
body can only throw because the API doesn't exist. A static condition
(mode, bundler) resolves at collection time into a normal Jest skip. A
lazy condition resolves at runtime, and when a lazy force-gate on a
describe is false, we skip the fixture build entirely — that's what
makes it usable for suites whose fixtures are build-incompatible with
the condition. (One caveat: Jest has no way to skip a test that's
already running, so these report as passing with a warning in the log,
not as skipped.)
Conditions live in a hand-written registry. I considered deriving the
lazy ones from the config schema automatically, but a gate is a claim
about which dimension of the test matrix explains a failure, and I'd
rather each of those claims be spelled out with a description.
Referencing an undeclared name fails the suite at collection time, so a
typo can't silently disable a gate.
The important design decision for lazy conditions is that they read the
fixture's _resolved_ config, never `process.env`. The env var isn't the
truth: `__NEXT_CACHE_COMPONENTS=true` only applies when the fixture
doesn't set `cacheComponents` itself, and config resolution implies
flags the fixture never mentions (`cacheComponents: true` alone turns on
`experimental.ppr`). Resolution happens in a child process, because
in-process `loadConfig` would leak the fixture's `.env` files into the
Jest worker. Suites with no lazy gate never pay for any of this.
The condition expression is parsed using a small grammar (also ported
from the React repo). An expression that doesn't parse fails the suite:
```ts
// @gate mode === 'start' && !cacheComponents
// @gate !(turbopack || rspack)
```
There's also a runtime version, mirroring React's `gate(flags =>
flags.enableFoo)`, for tests that run under both states but assert
differently (and for `it.each`, where the pragma can't attach):
```ts
import { gate } from 'next-test-utils'
it('renders the fallback', async () => {
if (await gate((conditions) => conditions.cacheComponents)) {
// PPR: the fallback is part of the static shell
} else {
// fully dynamic: the fallback streams in
}
})
```
It also accepts the pragma expression language as a string: `await
gate('cacheComponents && !dev')`.
Docs are in `test/lib/gate/README.md`; `test/unit/gate/` covers the
transform, the expression language, and the runtime.
52 lines
1.6 KiB
TypeScript
52 lines
1.6 KiB
TypeScript
/**
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* The seam between the gate runtime and the Next.js fixture a suite booted.
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*
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* A fixture is registered by `createNext()` as soon as it is set up, and
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* unregistered when it is destroyed. Registering the *instance* rather than a
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* config snapshot is what keeps `skipStart: true` suites and `next.build()` /
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* restart flows working: nothing is resolved until a gate actually asks, by
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* which point the fixture is up.
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*
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* Suites with no lazy `@gate` therefore pay nothing at all.
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*/
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import type { ResolvedNextConfig } from './resolved-config'
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/**
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* The part of `NextInstance` the gate runtime needs. Structural, so this module
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* stays independent of `test/lib/next-modes/base.ts`.
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*/
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export type GateConfigSource = {
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getResolvedConfig(): Promise<ResolvedNextConfig>
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}
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let activeFixture: GateConfigSource | null = null
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export function registerFixture(fixture: GateConfigSource): void {
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activeFixture = fixture
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}
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export function clearFixture(): void {
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activeFixture = null
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}
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export function hasFixture(): boolean {
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return activeFixture !== null
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}
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/**
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* Resolves the running fixture's config for a lazy condition. Memoization lives
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* on the instance, so repeated gates in one file resolve it once.
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*/
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export function getResolvedConfigForGates(): Promise<ResolvedNextConfig> {
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if (!activeFixture) {
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throw new Error(
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`This \`@gate\` condition is resolved from the running Next.js ` +
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`fixture's config, but no fixture is registered. Is this suite using ` +
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`\`nextTestSetup()\`? Conditions that are known up front (\`dev\`, ` +
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`\`turbopack\`, ...) do not need one.`
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)
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}
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return activeFixture.getResolvedConfig()
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}
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