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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.
60 lines
2.2 KiB
TypeScript
60 lines
2.2 KiB
TypeScript
import { evaluate, parse } from '../../lib/gate/expr'
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const run = (source: string, values: Record<string, unknown> = {}) =>
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evaluate(parse(source).node, (name) => values[name])
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describe('@gate expression language', () => {
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it('reads a bare condition by truthiness', () => {
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expect(run('a', { a: true })).toBe(true)
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expect(run('a', { a: false })).toBe(false)
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expect(run('a', {})).toBe(false)
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// A condition whose resolved value is an object (e.g. prefetchInlining).
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expect(run('a', { a: { maxSize: 2048 } })).toBe(true)
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})
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it('supports negation', () => {
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expect(run('!a', { a: false })).toBe(true)
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expect(run('!!a', { a: false })).toBe(false)
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})
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it('supports && and ||', () => {
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expect(run('a && b', { a: true, b: true })).toBe(true)
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expect(run('a && b', { a: true, b: false })).toBe(false)
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expect(run('a || b', { a: false, b: true })).toBe(true)
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expect(run('!a && b', { a: false, b: true })).toBe(true)
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})
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it('supports parentheses', () => {
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expect(run('!(a && b)', { a: true, b: false })).toBe(true)
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expect(run('!a && (b || c)', { a: false, b: false, c: true })).toBe(true)
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})
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it('compares against string literals', () => {
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expect(run("mode === 'start'", { mode: 'start' })).toBe(true)
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expect(run("mode === 'start'", { mode: 'dev' })).toBe(false)
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expect(run('mode !== "dev"', { mode: 'start' })).toBe(true)
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expect(run("mode == 'dev'", { mode: 'dev' })).toBe(true)
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})
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it('compares against booleans', () => {
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expect(run('a === false', { a: false })).toBe(true)
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expect(run('a === true', { a: undefined })).toBe(false)
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})
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it('collects the referenced condition names, deduplicated', () => {
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expect(parse("!a && (b || a) && c === 'x'").names).toEqual(['a', 'b', 'c'])
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expect(parse("mode === 'dev'").names).toEqual(['mode'])
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})
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it.each([
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['', 'Unexpected end of expression'],
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['a &&', 'Unexpected end of expression'],
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['(a', 'Missing closing `)`'],
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['a b', 'after a complete expression'],
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["'unterminated", 'Unterminated string'],
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['a # b', 'Unexpected character'],
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])('reports a syntax error for %p', (source, message) => {
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expect(() => parse(source)).toThrow(message)
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})
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})
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