meta/flow v0.198.0

on GitHub

Likely to cause new Flow errors:

• Implicit coercion of booleans to numbers is consistently disallowed. Previously, booleans could be implicitly coerced to numbers in addition expressions. Prefer explicitly converting booleans to numbers.
• Binary arithmetic errors are now reported on the expression rather than the operands, and use error code unsafe-arithmetic.
• keyof, undefined, never, unknown, and readonly are now reserved types. If you have a user-defined types of these names, rename them to something else.

New Features:

• TypeScript syntax helpers. To help people familiar with TypeScript syntax ramp up on similar Flow syntax:
  • Parse and error on keyof type operator, recommending $Keys<...> instead.
  • Parse and error on undefined type, recommending void instead.
  • Parse and error on never type, recommending empty instead.
  • Parse and error on unknown type, recommending mixed instead.
  • Parse and error on readonly applied to tuple and array type syntax.
  • Parse and error on usage of in/out/in out variance annotations.
  • Parse and error on as, as const, and satisfies cast expressions.
• Add a codemod to fix underconstrained-implicit-instantiation errors only detectable under LTI. You can run flow codemod annotate-implicit-instantiations --include-lti --ignore-suppressed --write .

Notable bug fixes:

• Fix a bug in LTI mode where some errors were hidden in implicit instantiation calls (e.g. Try Flow)
• Fix unsound behavior of sentinel refinement with unions of numeric types as tags (e.g. Try Flow)
• No annotation is required in LTI for callback parameters when the callee is a refined object member (e.g. Try Flow)

IDE:

• When typing in an object literal, entire method signatures from the object type will be suggested.
• Method signature autocomplete items are now visually distinguished from other kinds of autocomplete items.
• Fix manually triggering autocomplete on the last empty line of a file giving no results.
• Members from Object.prototype are no longer included in autocomplete results.

Parser:

• Fix parsing of for await (async of ...) (regressed in 0.197.0)
• Fix parsing of for (let in x) in non-strict mode
• Fix parsing of class fields named static
• Fix missing parse errors on keywords containing escape sequences (regressed in 0.180.0)
• Fix missing parse error when using await as a parameter in an async arrow function
• Fix missing parse error for export { ReservedWord as ... }
• Fix incorrect parse error on export * as ReservedWord from ..., which is now allowed
• Treat && and || as tokens when parsing types to improve error messages
• Parse the argument of the typeof type argument as a value, not a type, as it is a value

Library Definitions:

• Add Element.getAttributeNames(): Array<string>