facebook/flow v0.234.0

on GitHub

Likely to cause new Flow errors:

• Flow might catch more inexact incompatible with exact errors. example
• Fixed a bug that leads to Flow sometimes ignoring differences in call props of an object. New errors might be exposed. example
• We rewrite the way we generate types for annotations. We will now detect and error on trivially recursive types like type T = T or type Foo = typeof foo; const foo: Foo = .... In addition to this, you might see some errors being moved around.
• Fixed Flow Enums exhaustive checking logic when input is a generic.
• Invalid indexed access types with string index, like {foo: string}[string], will now error instead of silently making it any.

New Features:

• You can have a tuple spread of a generic in the parameter of a function and not have to supply the relevant type argument if that spread is the only spread in that tuple, and it is the last element of that tuple.
• Negative numbers are now allowed in Flow Enum values.
• Allow Flow Enums to be cast to their representation type when the cast expression is typed as a generic type.
• Added a new global type EnumValue<>, which represents all Flow Enum values. You can constrain the enum values to those with a particular representation type by supplying the type argument, e.g. EnumValue<string>.
• Added a new global type Enum<>, which represents all Flow Enums (this is a complement to the new EnumValue type). You can constrain the enums to ones which have a particular enum value, e.g. Enum<> is the same as Enum<EnumValue<>>, and the type of all enums with string representation types is Enum<EnumValue<string>>. These "abstract enums" have no know members, so you can't access members or exhaustively check them, but you can use methods such as .members(), .cast(), etc.
• Allow === comparison of abstract Flow Enums as well as Enums themselves with the same ID.
• You can now cast Flow Enum values to their representation type using .valueOf(), e.g. enum E {A, B}; const s: string = E.A.valueOf().

Notable bug fixes:

• We now error more reliably in the matching property tests, for example when the object part is a complex expression. example
• Fixed spurious errors in propagating type hints. example
• Infer type in a conditional type is now allowed to be underconstrained. When the true branch is taken, this underconstrained infer type will be pinned to the upper bound. example
• Add Enum and EnumValue to $NotNullOrVoid - previously there was no supertype for all enum values or enums.

IDE:

• We now show jsdoc information on component props with component syntax.