facebook/flow v0.337.0 on GitHub

Likely to cause new Flow errors:

Function.prototype.bind is now typed with TypeScript's CallableFunction.bind overloads, so errors in bound arguments are reported at bind, and a bound function's remaining parameters are a tuple type.
Function and Object no longer mean any and no longer trigger unclear-type errors. They are now interpreted as the prototypes of functions and objects. Code that assumed they meant any may get new errors.
Internal type Function$Prototype$Bind is removed.
Class method bind now uses the declared Function.prototype.bind overloads. Bound methods may now report tuple arity errors when used as callbacks that ignore extra arguments or omit nullable parameters, because their inferred parameters are represented as tuple rest parameters.

New Features:

Support assertion functions. If you relied on Flow's special handling of invariant, give it an asserts signature.
Execute runtime Flow syntax in CommonJS and ES modules with original stack locations through flow-node.
Support assertion narrowing through this and super, including receiver assertions.
Readonly now supports Array and ReadonlyArray types.

Notable bug fixes:

Honor opaque upper bounds in template interpolation and nullable subtyping.
Preserve nominal opaque inference when checking nullable targets.
Fixed spurious Recursion limit exceeded errors when checking conditions, match and other expressions whose type is a trivially recursive generic type alias.
Prevent unsound assertion narrowing when annotations refer to shadowed local declarations.
Qualified type references through a union of namespaces (e.g. (cond ? A : B).T via a local) now look up the type in each namespace instead of reporting it as missing.
Prevent saved-state startup and incremental match checking from crashing when a recheck is canceled.

Misc:

Parser:

Add missing AST fields and node types to the Flow parser output. implicitDeclare is now omitted unless true.
Emit TypeParameter.bound as a bare type node or null in ESTree output. Babel output retains the TypeAnnotation wrapper, and the TypeScript-to-Flow API translator generates extends bounds.
ESTree enum declarations now use a unified EnumBody node with string-or-null explicitType. Babel output retains its existing enum body types.
Parse typed function overload signatures in TypeScript implementation files.
Parse destructured parameters in TypeScript function types outside declaration files.
Parse optional class method signatures in JavaScript and TypeScript files.
Parse optional TypeScript constructor parameter properties.
Parse namespace export aliases and ambient exported members in TypeScript definitions.
Fix parsing of class modifiers before synchronous generator methods.
Support readonly T[] in unlabeled tuple elements and require parentheses when optional.

Library Definitions:

Add Intl.Segmenter and Intl.supportedValuesOf.
Add Intl.NumberFormat.prototype.formatRange and formatRangeToParts, and the ES2023 NumberFormat options; format accepts bigint and numeric strings.
String.prototype.localeCompare, toLocaleLowerCase and toLocaleUpperCase accept Intl.LocalesArgument; matchAll with a RegExp returns RegExpExecArray matches.
Float16Array.prototype.toLocaleString takes Intl.NumberFormatOptions.
Add ES2024 ArrayBuffer resizing, transfer, and constructor options.
Align Reflect APIs with TypeScript property, descriptor, key, and constructor definitions.
Reuse TypeScript's Float16Array declarations while preserving Flow covariance and callback compatibility.
Align Proxy APIs with TypeScript and check array elements against numeric interface indexers.