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@facebook-github-bot facebook-github-bot released this 31 Aug 21:02
v0.54.0
5c9deb4

Likely to cause new Flow errors:

  • Extending a polymorphic class must now explicitly specify the parent class's type args. That is, class A<T> {}; class B extends A {} is now an error, but class C extends A<string> {} or class D<T> extends A<T> {} is ok.
  • Improved accuracy of type checking calls of built-in methods (e.g. Object, Array, Promise)

Notable Changes:

  • Implemented private class fields, part of the Class Fields proposal.
  • Implemented "phantom" types (e.g. type T<Phantom> = any; type X = T<string>; type Y = T<number>, where X and Y are incompatible even though T doesn't use Phantom)
  • Unused suppression errors are now warnings instead
  • Improved errors involving polymorphic types, so that they now point to the source of the conflict, rather than the nested type args that are incompatible. This was a major source of errors in files other than where the problem was.
  • Improved errors involving structural subtyping, so that they now reference the objects that are incompatible in addition to the incompatible properties
  • Improved errors when an inexact object type flows into an exact type
  • Made rest parameters in object destructuring patterns sealed, and exact if possible
  • Improved definitions for some node fs functions
  • Improved performance by removing unnecessary caching

Misc:

  • Improved accuracy of type checking of React children in React.createClass
  • Fixed a bug related to instantiating a polymorphic type (e.g. type t = T<U>) with empty type args (e.g. var x: T<>)
  • Fixed polarity checking for property maps
  • Fixed a bug where polymorphic types were incorrectly checked for equality
  • Improved React definitions
  • Added a FLOW_TEMP_DIR env, equivalent to passing --temp-dir
  • Added a minimal libdef that defines the few things Flow can't run without, even when using no_flowlibs=true

Parser:

  • Added flow ast --strict to parse in strict mode without "use strict"
  • Added support for the RegExp dotAll ('s' flag) proposal
  • Added support for the private class fields proposal
  • Added support for destructuring defaults in assignments (e.g. given ({ x = 1 } = {}), x is 1)
  • Fixed issues related to let, yield, await, async, super and other reserved words
  • Fixed issues related to declarations in statement positions
  • Fixed issues related to destructuring patterns
  • Fixed issues related to IdentifierReferences, like shorthand object notation
  • Fixed issues related to class parsing, particularly new.target and async methods
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