facebook/flow v0.248.0

on GitHub

Breaking changes:

• Support for long deprecated predicate function (%checks) is removed. It will still parse, but all of them will error with unsupported-syntax, and %checks will be completely ignored for type checking purpose as if it doesn't exist.
• $TupleMap support is now removed. $TupleMap will now resolve to the global definition is there is one, or it will fail and the type becomes any.

Likely to cause new Flow errors:

• Support for the unsound $TEMPORARY$* types is dropped. If your codebase happens to have any of these types, you can replace them with there sound and well-documented equivalents:
  • Replace $TEMPORARY$object<{props}> with $ReadOnly<{props}> or {props}
  • Replace $TEMPORARY$array<T> with $ReadOnlyArray<T> or Array<T>
  • Replace $TEMPORARY$number<42> with number or '42'
  • Replace $TEMPORARY$string<"foo"> with string or "foo"
  • We have provided a flow-runner codemod via the flow-upgrade package to aid larger codebases with this conversion: yarn run flow-codemod replaceTemporaryTypes path/to/src.
• The inferred type for Object.freeze({ A: 'a', B: 'b' }) is now {+A:'a',+B:'b'} both locally within a file and when the object is being exported. This replaces an earlier unsound behavior where the type of A would opportunistically behaved either as string or 'a' depending on the context where it appeared.
• React string refs are now banned.
• contextTypes and childContextTypes in react class components are now empty typed, so declaring legacy context in React will be an error.
• Component syntax component and component types' ref prop now must have React.RefSetter<...> type.

Parser:

• Component type in parentheses can now be correctly parsed. e.g. type Foo = (component(x: number) renders Bar);
• Trailing comma is now allowed after rest parameter in component syntax components and component types.
• The v regex flag is now supported.

IDE:

• We now provide a code action to stub out a react component, at the location of an unbound JSX identifier.
• Component declaration/type without renders clause will no longer show renders React.Node on hover.
• Hovering on components will now consistently show its props and renders information. Previously, the information is omitted for component declarations.
• If we see : renders <annot> at the position that expects a render declaration, the quickfix will suggest removing : instead of replacing : with renders.

Library Definitions:

• Added type for util.stripVTControlCharacters for NodeJS.