facebook/flow v0.261.0

on GitHub

New Features:

• Bigint values inside of template literals now coerce to strings, e.g. `${1n}`. Addition with string (e.g. 1n + 'blah') is still banned.
• Add ability to resolve node package entrypoints/exports
• Flow now allows inference of type guards for simple expression arrow functions with one parameter. For example, in ["a", null].filter(s => s != null) it will automatically infer that the arrow function encodes a x is string type guard and will apply it on the input array resulting in aArray<string>. (try-Flow)
• module.system.node.root_relative_dirname will allow conditional mapping like module.system.node.root_relative_dirname='<PROJECT_ROOT>/foo' -> 'bar'. Under such config, import 'a' will only be resolved to <PROJECT_ROOT>/bar/a if import 'a' is in a file in the <PROJECT_ROOT>/foo directory. This feature will be helpful if you want to combine two flow roots with different module.system.node.root_relative_dirname config.

Likely to cause new Flow errors:

• When an opaque type is refined to be not null/undefined, we now refine the opaque type's upper bound rather than returning the opaque type unmodified.

Notable bug fixes:

• Flow will error more consistently on incompatible uses of refined string, number and boolean literal types (e.g. try-Flow)
• Fixed some cases of type filtering during type guard refinement (e.g. try-Flow)
• Fixed a bug of missing errors when certain functions were checked against interfaces (e.g. try-Flow)
• Fixed negation of refinement of type-guard functions with multiple parameters (e.g. try-Flow)
• Relaxed type-guard consistency checks when the function returns with true or false. (e.g. try-Flow)

Parser:

• We now provide parsing support for declare global {...} (using it will still result in an error). The AST will have the shape of

{
    "type":"DeclareNamespace",
    "loc": ...,
    "range": ...,
    "global":true,
    "id":{
        "type":"Identifier",
        "loc": ...,
        "range":...,
        "name":"global",
        "typeAnnotation":null,
        "optional":false
    },
    "body":{
        "type":"BlockStatement",
        ...
    },
}

Library Definitions:

• The global React$PureComponent is removed. If you want to refer to it, it needs to be imported from react.