facebook/flow v0.123.0

on GitHub

New Features:

• Added support for the babel react jsx transform with the react.runtime flowconfig
  option. When set to automatic the transform auto-imports jsx (the replacement for
  createElement) under a fresh name (unique of all existing names in the source).
  When set to classic it will continue transpiling jsx to React.createElement.

Notable bug fixes:

• We are now treating $Exact<T|U> as $Exact<T>|$Exact<U>. Before, when we checked
  against this type we would treat it like $Exact<T> & $Exact<U>, instead.
• Fix to prevent infinitely expanding recursive type applications of arrays (example).

Misc:

• Improvements in comment attachement in various kinds of AST nodes. These will
  help improve the accuracy of error suppression and various services that inspect
  comments (printing, showing documentation, etc.).
• $Exports<'m'> will now lookup module 'm' directly in builtins, instead of the
  environment.
• Extend union optimizations used on maybe predicate to also be applied in exists
  predicates.

Parser:

• The range around type cast expression now includes the parentheses. This follows
  the pattern of other constructs with mandatory punctuation like blocks, objects or arrays.