facebook/flow v0.336.0

on GitHub

Likely to cause new Flow errors:

• Calls such as Array.from can now infer narrower literal types, requiring explicit annotations where broader types are needed. Unconstrained class type arguments now use their bounds instead of empty.
• Flow now checks ref compatibility for JSX tags typed as string, exposing refs that assume a more specific element type.
• Explicit this parameters on methods in library definitions no longer need to accept the instance type.
• Generic rest-parameter inference can now expose previously hidden parameter-type errors. For example, (input: string, ...args: Array<unknown>) => void no longer satisfies (...args: TArgs) => R when TArgs is inferred as Array<unknown> (Try Flow example).
• Rest destructuring of exact tuples, e.g. const [first, ...rest] = t, now excludes preceding elements' types from rest.
• Variance annotations are now checked through tuple type spreads, so type T<out X> = [string, ...[X]] is an error.

New Features:

• Support tuple types with trailing rest elements, e.g. [string, ...Array<number>]. Array literals ending in array spreads and arguments collected by rest parameters can flow to these types.

Notable bug fixes:

• Declaration merging for interfaces and declare class now preserves variance annotations.
• Returns inside functions nested in a type guard function are no longer checked against the enclosing type guard.
• References inside declare namespace blocks now see members merged across blocks and library files.
• Functions and constructors are now accepted as builtin Function and Object values.
• Fixed spurious indexed-access errors involving recursive class type-argument bounds.
• Type arguments used in later tuple spreads, e.g. B in [...A, ...B], are now inferred instead of left underconstrained.
• Conditional types using infer on rest parameters now preserve the matched function's optional parameters and rest element in the inferred tuple, e.g. [number, ...Array<boolean>]. Matching functions with fewer parameters than the pattern and no rest parameter no longer produces underconstrained errors.

Misc:

• flow-upgrade now uses Flow parser packages and requires Node 18 and Prettier 3.

Parser:

• Correct JavaScript source columns after characters represented by surrogate pairs.

IDE:

• Hover Go to links no longer include the hovered declaration itself.

Library Definitions:

• Intl is now a builtin namespace with TypeScript-compatible definitions through ES2020, including Collator, NumberFormat, DateTimeFormat, PluralRules, RelativeTimeFormat, Locale, DisplayNames, getCanonicalLocales, and formatToParts for dates and numbers.
• The legacy Intl$CollatorOptions, Intl$DateTimeFormatOptions, and Intl$NumberFormatOptions aliases now match TypeScript. Intl.DateTimeFormatPartTypes includes 'unknown', and locale-aware Date methods accept Intl.LocalesArgument and Intl.DateTimeFormatOptions.
• The global LocalesArgument type is now Intl.LocalesArgument. Library declarations such as flow-typed's declare var Intl hide the builtin namespace and must be removed.
• React.ElementConfig is removed; use React.ComponentProps instead.
• Typed arrays gain findLast, findLastIndex, toReversed, toSorted, and with, and their constructors can be called without arguments. For types other than Float16Array, findLast narrows its result with a type-guard callback. Callbacks to findLast and findLastIndex can no longer annotate this.
• Float16Array now matches TypeScript's declaration, including its from overloads. length, byteLength, and byteOffset are read-only, find and findIndex predicates must return boolean, and callbacks can no longer annotate this.
• Add RegExp indices and flags, well-formed string methods, bigint Atomics, Error.isError, Promise.try, Atomics.pause, and additional ArrayBuffer and Date constructor signatures.
• Add TypeScript signatures for Array.fromAsync.
• AggregateError.prototype.errors is now typed any[], matching TypeScript.
• Decorator definitions now match TypeScript: ClassDecorator accepts classes, decorator context and metadata types are available, and Function includes [Symbol.metadata].
• Add DisposableStack, AsyncDisposableStack, SuppressedError, Disposable, and AsyncDisposable. AsyncGenerator now extends AsyncIteratorObject and includes [Symbol.asyncDispose].