v0.230.0
facebook-github-bot
released this
06 Mar 02:10
·
1120 commits
to main
since this release
Likely to cause new Flow errors:
- We now put value exports and type exports into two different namespaces. It means that we will now consistently error on places where you try to import, re-export, or use a imported type as a value. This change also makes certain patterns that happen to work in the past no longer work, e.g.
// a.js
export type Foo = string;
// b.js
const A = require('./a');
module.exports = {...A};
// c.js
// previously allowed, no longer allowed
import type {Foo} from './b';
- We have allowed function parameters to refer to each other for a while now. However, we didn't implement the analysis correctly for exported functions, which causes inconsistent behaviors. This is now fixed e.g.
// a.js
// we incorrectly resolve x to refer to
// be external to the function params,
// which is a global in this case
export function foo(x: string, y: typeof x) {}
// b.js
import {foo} from './a';
foo("", 3); // no error before, errors now
- Previously, we allowed assignment to any globals, regardless of whether it's a type or value. Therefore, both were allowed in
Array = 3; $ReadOnlyArray = 2;
Now the latter is banned. - Flow now consistently bans referring a type-only global as value
- Some bad annotations that cause
value-as-type
orrecursive-definition
errors will no longer affect which branch to take in overload resolution.
New Features:
- Flow now supports typeof with type arguments
type T = typeof foo<string>
. This syntax is supported in prettier since v3.1. If you previously enabled the flagtypeof_with_type_arguments=true
, you need to remove it. - Flow now supports explicit type arguments on JSX. e.g.
<Foo<string, _, number >propA='d' />
. Note that some type arguments can be inferred using the_
syntax. - Flow now supports the same
NoInfer
intrinsic that will be available in TypeScript 5.4. - Under
experimental.ts_syntax=true
, Flow will- Automatically translate TypeScript's readonly on tuple and array types into Flow equivalent
$ReadOnly<[...]>
and$ReadOnlyArray<...>
without error. - Automatically translate TypeScript's keyof into Flow equivalent
$Keys
without error. Note that there are behavior differences between$Keys<>
andkeyof
right now (flow, TS), so use it with caution. - Automatically translate TypeScript's
unknown
never
andundefined
into Flow equivalentmixed
empty
andvoid
without error. - Support TypeScript's variance annotation
readonly
in
out
,in out
without error.
- Automatically translate TypeScript's readonly on tuple and array types into Flow equivalent
Misc:
experimental.ts_syntax
is now always on in https://flow.org/try.