facebook/flow v0.188.0

on GitHub

Likely to cause new Flow errors:

• Previously we supported a weird JS runtime rule for constructor returns when you call new SomeClass:

  • If the returned value is primitive, then it's ignored and the instance will be returned instead.
  • If the returned value is object like, then the return object will be the eval result of new SomeClass.

  This is confusing, and we dropped support for this feature in this release. Now we enforce that all class constructors must return void.

• Fixed a bug preventing refinements from being invalidated in inline && expressions: examples like typeof x === 'number' && reassignXToString() && (x: number) were passing even if reassignXToString() assigned a a string value to x.

New Features:

• flow codemod annotate-lti is now provided to help prepare your codebase to enable the enforce_local_inference_annotations=true flag. In order to eventually enable local type inference, we will require additional annotations in places we can't contextually type your code. You can enable the annotation enforcement now with enforce_local_inference_annotations=true in flowconfig. This flag enables the behaviors of all the following experimental flags, which will be deleted in the next release:

experimental.enforce_local_inference_annotations=true
experimental.enforce_this_annotations=true
experimental.enforce_class_annotations=true

To migrate your codebase, you can run the following codemod to prepare your codebase for the new requirement: flow codemod annotate-lti. Check out an upcoming blog post for more details.

Misc:

• Remove the file_watcher.watchman.survive_restarts flowconfig option, which was deprecated in 0.158.0. We will always try to survive Watchman restarts.
• Remove the experimental.refactor flowconfig option. It has been true by default since v0.158.0.

Library Definitions:

• Updates the typing of fs.promises.readdir() to reflect the possibility of passing withFileTypes: true and receiving an array of Dirent objects