facebook/flow v0.335.0

on GitHub

Breaking Changes:

• Removed the legacy builtin_lib=flowlib and builtin_lib=flowlib-with-lib-dom-d-ts options.
• Removed the Flow config options exact_by_default, experimental.always_generalize_jsx, experimental.fast_symlink_resolution, experimental.importable_global_libdefs, experimental.interface_dictionary_typing_fix, experimental.new_this_typing, experimental.opaque_type_new_bound_syntax, saved_state.allow_reinit, saved_state.direct_serialization, and saved_state.reinit_on_lib_change. These options had been enabled by default and only accepted true.

Likely to cause new Flow errors:

• Symbol and Promise now use TypeScript-style instance and constructor interfaces. Code relying on their previous class typing may see different errors.
• Some JSX expressions that were previously considered underconstrained now infer unknown.
• Fixed type argument inference that incorrectly used a bound or unknown. More underconstrained errors may appear.
• String.prototype.replaceAll now has separate overloads for a replacement string and a replacer function, matching TypeScript. Passing a union of these types is an error.
• RegExpMatchArray.groups is now optional and cannot be null, and RegExp.prototype.dotAll is read-only, matching TypeScript.
• new $ReadOnlyArray now causes an error.
• Symbol() now only accepts a string | number description, and Symbol.keyFor returns string | void, matching TypeScript.
• Deprecated syntax now consistently causes errors, including in library definition files.
• Type arguments of a polymorphic value flowing to a non-polymorphic type are now solved, which can surface previously hidden errors.
• React.PropsOf now uses React.ComponentProps to find component props. Additional errors may occur.

New Features:

• Support assertion functions exported through CommonJS, assertion calls in return position, and assertion calls in arrow expression bodies.
• The undefined type can be used in library definitions, where it means void.
• flow-remove-types supports abstract classes, abstract members, override modifiers, satisfies, optional class fields, and additional type-only imports and exports.
• Template literals infer precise types in const declarations and annotated initializers.

Notable bug fixes:

• as const on template literals infers template literal types like TypeScript.
• Implicit instantiation can infer a type argument through React.ComponentProps and other conditional types with infer.
• Interfaces with construct signatures no longer print a spurious this parameter in error messages and hovers.
• this-typed methods inherited from builtins such as typed arrays now return the subclass.
• Exported declare class declarations extending builtins such as Error, Map, Set, or Date now inherit the builtin's statics and constructor.
• Arguments of new X(...) are now contextually typed when X is annotated with the typeof of a constructor interface value.
• typeof x === 'function' now refines builtin constructors such as Map and Symbol, and interfaces with call signatures, as functions.
• User-defined assertion conditions check member access in test context.
• Recognize ESM default imports of CommonJS assertion functions and callable objects with asserts call signatures.
• instanceof and declare class ... extends now use the prototype of a constructor interface that has no construct signature, instead of narrowing to empty or reporting "not inheritable".
• Fixed a memory leak in type signature parsing that inflated server memory on large codebases.
• Fixed checking interfaces that extend classes, including object values and multiple generic class supers.

Misc:

• React.ElementConfig is deprecated in this version and will be removed in the next version. Use React.ComponentProps instead.
• The unnecessary-invariant lint is renamed to unnecessary-assertion; the old name is still accepted.
• Constructor errors and variance check errors now print types instead of descriptions such as "object type", "module", or "exports".
• Unary arithmetic on a maybe-typed operand reports null and void separately instead of "null or undefined".
• Record type utility errors name the utility (Partial, Required, or mapped type).

Parser:

• Store abstract property annotations in typeAnnotation and emit value: null.

IDE:

• Hover on flow.org/try now shows types framed as declarations, matching the VS Code extension.
• Autocomplete and go-to-definition on instances of classes extending builtins such as Map, Set, Error, and Date now show the builtin's instance members.
• JSX attribute autocomplete on a union or intersection of components offers the props of the components the element is checked against.
• Go-to-definition on a JSX attribute of a union or intersection of components uses the props of the components the element is checked against.
• Find-references on a JSX attribute of an intersection of components finds the attributes passed to the branch the element is checked against.
• Qualify React.ComponentProps in generated type annotations.

Library Definitions:

• React.ComponentProps<'div'> now includes the optional ref prop.
• Added Promise.withResolvers.
• The type parameters of Map.groupBy are now ordered <K, T>, matching TypeScript.
• RegExp.prototype[Symbol.matchAll] is now a method and RegExpStringIterator an interface, matching TypeScript.