flow-parser

Likely to cause new Flow errors:

• Modified the behavior of instanceof checks and other refinements to more consistently detect when impossible or invalid refinements are made. This will result in new errors in such cases.

New Features:

• Improved error messages by providing a suggested property when properties are missing in a conditional context.

Notable bug fixes:

• Fix "matching property" checks with generic inputs (try-Flow). Thanks @gnprice for bringing up this issue and exploring potential causes!
• Fixed a bug where the use of certain utility types in polymorphic functions caused errors to not be reported (e.g. try-Flow)
• Fix a bug where the [method-unbinding] error was reported twice

Misc:

• OCaml version 4.12.1 is required to build Flow
• React default exports are now inexact, as technically this can include unknown properties (experimental features)

Parser:

• Fixed a bug where type parameter instantiations that start with < (e.g., f<<T>()=>S>()) would be incorrectly parsed as the left shift operator.

Library Definitions:

• Add bindings for NodeJS util.types

Bug Fixes:

• Exact objects are treated as truthy in logical expressions
• Add support for operations on $Values<> types in an export position (e.g. Try Flow)
• Respect the order of module.file_ext when resolving imports. Before, they were tried alphabetically.

Misc:

• Change signature-verification-failure from a lint to a normal error. It is no longer valid in the [lints] section of .flowconfig.
• Improve performance of IDE commands when Flow is busy typechecking

Likely to cause new Flow errors:

• Disallow duplicate member names in classes.
• Error if an interface is imported as a value.
• The experimental.new_merge option becomes true by default. This is an internal change in the way file signatures are computed, but may cause new [invalid-exported-annotation] errors when a file exports types that include certain kinds of complex operations, such as projections over complex utility types like $ObjMap. These errors can be fixed by replacing these complex types with simpler ones. In certain cases, the newly added $KeyMirror and $ObjMapConst types (that are exempt of this restriction) can be used instead.

Notable bug fixes:

• Fix Watchman file watcher on Windows when an include path doesn't exist.
• Fix a parse error when a newline appears after a class method definition's name.

Parser:

• Add support for parsing logical assignment operators (thanks @strub).
• Fix compliance with estree: export * as x from 'y' is now an ExportAllDeclaration with an exported key.
• Permanently enable parsing of nullish coalescing, and remove the esproposal_nullish_coalescing option.
• Permanently enable parsing of optional chaining, and remove the esproposal_optional_chaining option.
• Permanently enable parsing of class static fields, and remove the esproposal_class_static_fields option.
• Permanently enable parsing of class instance fields, and remove the esproposal_class_instance_fields option.

Library Definitions:

• Make some options parameters in node's fsPromises optional.

Another light release due to the new year. Changes are mainly internal -- refactoring or progress towards future features.

This release is light on changes due to the holidays. Happy New Year!

• Improve performance

Notable bug fixes:

• Improve performance of IDE requests when using lazy mode and saved state
• Improve performance of checking union types by optimizing enums more aggressively

Notable bug fixes:

• Fix crash when moving a module introduced in v0.167.0

Notable bug fixes:

• Error on invalid @flow modes

Misc:

• Remove the --profile, --json and --pretty flags from flow force-recheck
• Reduce usage of shared heap space

Library Definitions:

• Add support for Node inspector
• Improve Document definition
• Add document.contentType
• Add 'navigate' as valid request ModeType (Thanks @comp615)

• Fix a crash introduced in 0.166.0

• Improve recheck performance on large projects
• No longer support flow check-contents on non-Flow files by default; pass --all to force it.
• No longer attempt to provide LSP documentHighlight on non-Flow files.
• Remove legacy "weak" mode. The --weak CLI flag and weak=true flowconfig option have been removed.

Notable bug fixes:

• Improve performance of signature help
• Fix a bug that caused rechecks to be unnecessarily invalidated and restarted

Likely to cause new Flow errors:

• The Flow parser now requires that variables declared using the declare var syntax be annotated with a type. declare var x; is now illegal.

Notable bug fixes:

• No longer attempt to provide autocomplete or flow autocomplete on non-Flow files.
• Fix a crash when deleting a file in lazy mode
• Fix a bug that prevented some code actions from adding type imports for export default class definitions

New Features:

• exports/module.exports can no longer be read from in a module (e.g. exports.foo) to eliminate this usage of unsealed objects - you can refactor your code to directly reference foo instead, or just use ES modules (e.g. export const foo = ...)
• Improved autocomplete for the targets of typeof type annotations.
• Support for finding references and renaming has been removed. While these features often worked well, they also caused extremely bad performance and crashes. We hope to reimplement these features as soon as we can.
• When displaying types, always use indexed access types for $ElementType and $PropertyType utilities.
• Remove indexed_access option, it's always enabled now (was on by default before if the option was omitted).

Notable bug fixes:

• Fix an issue where the refactor code-action would hang on large inputs.
• The exports of a file with no value exports are typed as an exact empty object rather than an unsealed object. Common errors which resulted from this are accidentally doing import typeof Foo rather than import type {Foo}
• Fix error causing LSP requests to fail.
• Fix calling watchman on Windows.
• Fix soundness issue when comparing polymorphic types (example try-Flow).
• Fix handling of duplicate bindings in signature builder.
• Improve error messages and type-at-pos results around $ExactT<...> type annotations.
• Fix referencing this in a JSX title member.
• flow coverage now returns 0% for non-@flow files; pass --all to also check non-@flow files.
• No longer attempt to provide definition or flow get-def on non-Flow files.
• No longer attempt to provide hover or flow type-at-pos on non-Flow files
• Update to latest LSP 3.17 beta definition of CompletionItemLabelDetail

Library Definitions:

• Fix navigator.clipboard.write type and add ClipboardItem (thanks @Egrodo).
• Add node.js fs.copyFile overload to support the case where the mode param is not specified (thanks @Brianzchen).

Misc:

• Removed the flow suggest command.
• Improve codemod CLI error handling (Thanks @gnprice).
• Changed scheduling of LSP commands in parallel with typechecking, to prioritize commands.
• Removed flow find-refs command.
• Removed the --expand-type-aliases flag from all Flow commands, it has caused several performance and non-termination issues without providing much value.
• Improved codebase quality (thanks @gnprice).

Parser:

• Invalid typeof type annotations, where the argument to typeof is a not a variable or member expression, are now parse errors rather than type errors.

New Features:

• The deprecated * type is now an alias to any. You can use flow codemod replace-existentials, which is available in previous versions of Flow, to upgrade your codebase to not use *. This codemod command will not be available in the current or future versions of Flow.
• Add (experimental) codemod to annotate variables that cause constrained write errors in future Flow versions.
• Add (experimental) codemod rename variable names that are reused with different types.
• Add --include-comments and --include-locs flags to the flow ast command.
• Add $ObjMapConst<O, T> builtin type, alias for $ObjMap<O, () => T>.

Notable bug fixes:

• Fix bug in $KeyMirror so that it respects the optionality of its arguments.
• Type JSON as object rather than a class. This prevents code such as new JSON() which is a runtime error.

Library Definitions:

• Add InputEvent.dataTransfer
• Declare AggregateError class - fixes #8764 (thanks @lachlanhunt).
• Improve UIEvent, InputEvent and KeyboardEvent types.

Misc:

• Fix typo in CONTRIBUTING.md (thanks @jereef).
• Clarify comments for ConcretizeTypeAppsT logic after Subtyping_kit refactor (thanks gnprice).

Parser:

• Fix a bug that allowed comments after the # in private identifiers.

• Fix a bug where errors in node_modules were shown in lazy mode. It is now consistent with non-lazy mode.

Likely to cause new Flow errors:

• As part of our work on Local Type Inference, unannotated variables now require a non-null value to be assigned to them at some point in the program. If a variable is intentionally only null, it can be annotated with null (let x: null = null); if only undefined, then it can be annotated with void (let x: void;).
• Function and class names can no longer be reassigned, even when not exported
• Fix positioning of [missing-type-arg] errors

New Features:

• Add $Partial utility type. This utility converts all of an object's or interface's named fields to be optional, while maintaining all the object's other properties (exactness, sealedness, etc).

Notable bug fixes:

• Improve performance of strict_es6_import_export
• Fix an infinite recheck loop when deleting a file when using saved state
• Fix a bug where the server would stop after running a CLI command if the server was starting with --autostop

Misc:

• Type import.meta as object
• Fix jsdoc support on imported declare function
• Make string literal autocomplete obey format.single_quotes setting
• Improve reliability of "refactor" code actions

Likely to cause new Flow errors:

• Only consider variables as "constlike" if their assignments are within their declarations. This fixes cases of unsoundness. example.

New Features:

• Add hierarchical document symbol support to the LSP. Improves VS Code's Outline pane, breadcrumbs and symbol search.
• Autocomplete now includes primitive types like string and number, as well as utility types like $Call and $Keys.

Notable changes:

• Significantly improved overall performance.

Notable bug fixes:

• Unknown or redundant settings in the flowconfig [lints] section are now ignored when passing --ignore-version.
• Improve results of type-at-pos on $ReadOnly types.

flow-remove-types:

• Added a Jest transformer, flow-remove-types/jest

• The fix in 0.160.1 didn't fully fix the regression in 0.160.0. It, and the original "fix" from 0.160.0 are reverted.

• Fix a regression in 0.160.0 that caused suppressions to be ignored upon editing files in some cases when using lazy mode.

New Features:

• The ide, fs and watchman lazy modes have been merged into a single mode. The new mode is now SCM-aware with or without Watchman; when the server starts, it queries Git or Mercurial and checks all existing local changes (changes since the mergebase).

  The file_watcher.watchman.mergebase_with config option has been renamed to file_watcher.mergebase_with; set this to the name of your default remote branch (e.g. origin/main).

  Flowconfig setting migration:

  • lazy_mode=watchman -> lazy_mode=true, file_watcher=watchman
  • lazy_mode=fs -> lazy_mode=true
  • lazy_mode=ide -> lazy_mode=true
  • lazy_mode=none -> lazy_mode=false

• Added parser support for import.meta

• Added type checking support for new.target and import.meta as mixed

Library Definitions:

• Add type for queueMicrotask

Notable bug fixes:

• Improve codemod performance on large codebases
• Fix a bug that could cause "unused suppression" warnings to appear incorrectly when using lazy mode

New Features:

• Add support for git to watchman lazy mode. Git projects using file_watcher=watchman and lazy_mode=fs can now upgrade to lazy_mode=watchman.
• Add codemod to convert $ObjMapi<T, <K>(K) => K> to $KeyMirror<T>. Run it via flow codemod key-mirror [OPTION]... [FILE].

Library Definitions:

• Add devicePixelRatio global (thanks @Brianzchen)

New Features:

• Add support for private class methods, implementing both the instance and static proposals! (thanks to our intern, @SamChou19815)
• Add an "Organize Imports" code action which sorts and groups the imports at the top of the file.
• Add an "Add all missing imports" code action which auto-imports all unambiguously undefined variables in the given file.

Notable changes:

• Fix a bug where private class fields like #foo: () => 'foo' could not be called, leading to workarounds like this.#foo.call(this)
• Fix a crash when hovering over a type annotation that is recursive in a parameter default
• Fix a crash when autocompleting inside an object literal with a recursive type
• Fix order of auto-import code actions
• Fix issue with utility types nested in $NonMaybeType<...>
• Fix Go to Definition on module reference strings (e.g. if module.system.haste.module_ref_prefix=m#, "m#Foo" will jump to the Foo module)
• The file_watcher.watchman.survive_restarts setting is now true by default. This setting is deprecated and will be removed in a future version.
• The --retry-if-init CLI flag has been removed. Setting it to false previously caused the command to error if the server was already running but not yet ready. Instead, use --timeout to avoid waiting too long.

Parser:

• Significantly improved parser performance
• Private methods are no longer a parse error

flow-remove-types:

• Fix to remove variance sigils on class properties (thanks @mischnic)

Likely to cause new Flow errors:

• Add a new error for unreachable code occuring in a loop after a conditional with mixed break and continue branches.

New Features:

• LSP extract to function/method/constant/class fields/type alias is enabled by default. These refactors will show up under after selecting some code. They can be disabled by adding experimental.refactor=false to the .flowconfig.
• Add an eslint plugin, eslint-plugin-fb-flow, for eslint rules from the Flow team. The first rule is use-indexed-access-type to encourage the use of indexed access types (https://flow.org/en/docs/types/indexed-access/).
• Add another eslint rule to lint against explicit exact by default syntax (fixes #8612).
• Add a command to update-suppressions to the flow tool (fixes #8384).

Library Definitions:

• Better coverage of the MediaTrackSettings API.
• Improve types for ResizeObserver (fixes #8693).

Misc:

• Upgrade to OCaml 4.10.2.

New Features:

• Cross-module autocompletion and code actions that fix missing import declarations are now enabled by default. This was experimental since 0.143.0. Can be disabled per project with the autoimports=false flowconfig option, or per user with the flow.suggest.autoImports LSP configuration.

Library Definitions:

• Enhance the builtin Node.js module types (thanks @isker).

Fix bug in shared memory garbage collection which caused Flow to crash.

Likely to cause new Flow errors:

• Ban the use of this inside of object methods (see https://medium.com/flow-type/sound-typing-for-this-in-flow-d62db2af969e).

Notable bug fixes:

• Fix a bug with name collisions in declared modules (fixes #8604).
• Prevent showing identifiers for autocomplete of method names.
• Preserve interfaces when used with the $ReadOnly utility

Library Definitions:

• Add support for fs promises (thanks @atabel).

Likely to cause new Flow errors:

• Added type checking for this parameters of functions (see https://medium.com/flow-type/sound-typing-for-this-in-flow-d62db2af969e).

New Features:

• Added codemod to cleanup the use of soon to be deprecated existential type (e.g. *). It can be run via flow codemod replace-existentials --write ..
• Added IDE quickfix for optional chaining when accessing an object that is nullable.

Notable bug fixes:

• Fixed crash related to a missing method unbinding error case.
• Fixed crash from calling the flow binary with an unknown argument.

Library Definitions:

• Fix MediaSource readyState to match the spec, "opened" -> "open" (thanks @sompylasar).

Misc:

• Remove experimental.this_annot config option and permanently enable now that our core lib defs rely on this feature.
• Remove prevously defaulted on new_check config option for the new check mode that uses significantly less RAM for large projects.

Likely to cause new Flow errors:

• Enforce that interfaces are supertypes of objects and classes. Also prevent objects from being a supertype of a class.
• Improve soundness of this typing by banning the unbinding of class methods (see https://medium.com/flow-type/sound-typing-for-this-in-flow-d62db2af969e).

New Features:

• You can require an exhaustive check of an enum in a switch statement that includes a default branch. This is enabled with the comment // flowlint-next-line require-explicit-enum-switch-cases:error.
• Autocomplete for object keys.
• Introduce a flow fix command to apply autofixes from the command line to a list of files.
• Enable a new check mode that uses significantly less RAM for large projects.

Notable bug fixes:

• Fix a bug that allowed nested anonymous functions inside a default export.
• Using the --ignore-version flag also prevents Flow from crashing when an invalid option is in the .flowconfig.

Library Definitions:

• Support the options parameter for require.resolve. (thanks @skeggse)
• Return a TypedArray instead of void from TypedArray sort function. (thanks @goodmind)
• Return a DOMStringList instead of a string array from IDBDatabase.objectStoreNames. (thanks @bnelo12)

Misc:

• Add --binary to the flow version command to see the path to the current binary.
• Prevent the LSP from exiting when an invalid option is in the .flowconfig.
• Autofix for a method-unbinding error to replace the method with an arrow function.
• Autofix for a class-object-subtyping error to replace the object type with an interface.

Likely to cause new Flow errors:

• Fixed an issue with refinement invalidation for variables without initializers or that are written to before they're declared. You may see both new errors from improved invalidations, and some unnecessary invalidations will be removed.

Notable bug fixes:

• Fixed the behavior of unary not operator on type applications

Library Definitions:

• Add Symbol.asyncIterator (thanks @goodmind)
• Add missing methods to HTMLTableSectionElement (thanks @vitoreiji)
• Fix nullability of various DOM table properties
• Fix type of MediaRecorder constructor options
• Improve node crypto types (thanks @juodumas)
• Improve node cluster.worker type (thanks @magicmark)

New Features:

• Add Smart Select IDE feature. This allows you to expand or shrink your selection based on the surrounding code. For example you might expand from an identifier to the containing expression, to the whole statement. In vscode, you can do this via ctrl+shift+cmd+(left or right arrow).
• Add Enum getName(value: TEnum): string method. Given a value of the enum type, this returns the string representation of the name of the member. You will also need to update to the latest flow-enums-runtime package.

Notable bug fixes:

• Update annotate-exports codemod to add lowercase react instead of React (thanks @meandmax!).

Misc:

• Improve developer setup on Windows by exposing internal setup scripts and updating the Windows setup README.md.
• Enable cache_live_errors_artifacts and cache_signature_help_artifacts config options by default.
• Improve performance and reliability of Watchman integration.
• Error for use of super outside of class methods added in 0.148.0 has been removed.

Library Definitions:

• Update React types for React 18 release.
• Update the Map, WeakMap, Set and WeakSet constructors' iterable param to be optional as per the ECMAScript spec.
• Add typing for PageTransitionEvent as per the HTML spec (thanks @bripkens!).
• Added support for stepUp and stepDown in HTMLInputElement declaration as per the HTML spec.

New Features:

• Suggest string literals in autocomplete in positions where string literal unions are expected.

Notable bug fixes:

• Use bracket syntax for autocomplete when autocompleting a property name that is not a valid identifier.
• Require the "main" property of package.json to have a valid Flow extension for the file to be considered.
• Fall back to .js extensions even when a module name looks like a resource file (e.g. ./a.svg will look to ./a.svg.js).
• Fix a crash that occurred when checking a this parameter with a generic.
• Make $NonMaybeType<empty> evaluate to empty.
• Honor format config options in more cases in code actions and codemods.
• Fix PointerCapture library definitions (thanks @malectro!).

Misc:

• Remove experimental observedBits param to React's useContext libdef.
• Add caching to live errors and signature help, to speed up IDE interactions (currently behind temporary flags).
• Introduce format.bracket_spacing option which affects code output (such as code actions).
• Improve the sorting of autoimport suggestions that have the same name, so that the module's file extension is not considered.

New Features:

• Suggest string literals in autocomplete in positions where string literal unions are expected.

Notable bug fixes:

• Use bracket syntax for autocomplete when autocompleting a property name that is not a valid identifier.
• Require the "main" property of package.json to have a valid Flow extension for the file to be considered.
• Fall back to .js extensions even when a module name looks like a resource file (e.g. ./a.svg will look to ./a.svg.js).
• Fix a crash that occurred when checking a this parameter with a generic.
• Make $NonMaybeType<empty> evaluate to empty.
• Honor format config options in more cases in code actions and codemods.
• Fix PointerCapture library definitions (thanks @malectro!).

Misc:

• Remove experimental observedBits param to React's useContext libdef.
• Add caching to live errors and signature help, to speed up IDE interactions (currently behind temporary flags).
• Introduce format.bracket_spacing option which affects code output (such as code actions).
• Improve the sorting of autoimport suggestions that have the same name, so that the module's file extension is not considered.

New Features:

• Added autocomplete for member expressions that use bracket notation

Notable bug fixes:

• Improved typechecking for expressions like obj[Symbol.iterator]. This is now correctly typed as the object type's @@iterator property.

Misc:

• Removed esproposal.class_instance_fields, esproposal.class_static_fields, esproposal.decorators, esproposal.export_star_as, esproposal.nullish_coalescing and esproposal.optional_chaining flowconfig options which have been deprecated since v0.135.

Likely to cause new Flow errors:

• We now error if the RHS of instanceof is not an object, e.g. x instanceof null. This catches 'instanceof' is not an object runtime errors.
• Using super outside of class methods, e.g. in arrow and function properties, is now an error.

Library Definitions:

• Add static from to stream$Readable (thanks @agalatan).

Notable bug fixes:

• Fixed autoimports to not suggest vars already in scope.
• Fixed autoimports to reuse existing imports if they exist.
• Fixed autoimports to correctly sort imports of the same name.
• Fixed null from being a subtype of an empty interface e.g. (null: interface {}) // Error (thanks @mrtnzlml for the report).

Misc:

• flow refactor experimental command removed. Instead, use the LSP textDocument/rename request.
• Removed the experimental.new_signatures flowconfig option as well as the --old-signatures opt-out command line flag.

Likely to cause new Flow errors:

• This release includes some significant architectural changes that fix bugs, improves performance, and may cause Flow to find more errors.
• Fixed a bug where "maybe types" like ?{c: number} did not properly error when used with utility types $PropertyType and $ElementType. null and undefined do not have properties nor elements.
• Object.prototype properties like toString and hasOwnProperty are no longer allowed to be accessed as global variables, which was previously allowed because window is an object.

New Features:

• Added Linux ARM64 support. A precompiled binary is provided, including through flow-bin.

Notable bug fixes:

• Improved the error message when getting properties on null and undefined
• Fixed running flow lsp on symlinked root directories

Misc:

• Removed support for @flow weak, which was a rarely-used mode in which missing annotations were treated as any. It is equivalent to suppressing any type errors that result from just using @flow. So to migrate, suppress the new errors and remove weak.
• Fixed a bug in which the built-in library definitions could be missing
• Fixed an obscure crash when using Watchman and Mercurial
• Added support for a flow.suggest.autoImports LSP setting to disable autoimport suggestions in autocomplete (currently requires autoimports=true to be enabled in .flowconfig)

Library definitions:

• Added support for node's assert strict mode (thanks @goodmind)
• Added support for .webp resources (thanks @TomasBarry)
• Added missing Brotli APIs to the zlib module (thanks @isker)
• Added missing methods to tty.WriteStream (thanks @reyronald)
• Changed process.exit to return empty

Parser:

• Fixed a regression in 0.146 where flow_parser.js defined some global variables

Likely to cause new Flow errors:

• The rules around when refinements are invalidated have been strengthened for increased accuracy, and Flow will now invalidate refinements in a number of locations where they were not previously invalidated. This may expose new Flow errors due to variables that were previously refined to a more specific type now being treated as the unrefined, more general type.
• Object literals now have covariant subtyping with interfaces
• Interface optional properties are no longer unsafely covariant in all cases
• Interfaces with indexed properties are now properly supertypes of classes/objects with named properties matching the indexer
• interface {} is no longer a supertype of void and mixed

Notable bug fixes:

• Properties that begin with a . were sometimes being ignored by Flow, which has now been fixed

Library Definitions:

• Added missing attributes to PerformanceResourceTiming library definition (thanks @MIGreenberg)
• Added withFileTypes option to readdir and readdirSync (thanks @mrtnzlml)
• Added composedPath function to Event library definition (thanks @Brianzchen)
• Added JSDocs to Event library definition and made most properties read-only

Misc:

• New flowconfig options to set garbage collector parameters for workers. The new flowconfig options are gc.worker.custom_major_ratio, gc.worker.custom_minor_ratio, gc.worker.custom_minor_max_size, gc.worker.minor_heap_size, gc.worker.major_heap_increment, gc.worker.space_overhead, and gc.worker.window_size.

Likely to cause new Flow errors:

• Correctly typecheck destructuring defaults in function params. e.g. function i({name = 1}: {| name?: string |}) {} was previously not an error.

New Features:

• New options added to flow_parser.js to support configuring comment output. comments enables comment attachment and all_comments enables the legacy list of all comments.

Notable bug fixes:

• Correctly handle import paths within node_modules for auto imports.
• Fixed a bug in Go to Definition on imported values that skipped all the way to the value's type definition instead of the value's definition.

• Improved generic type checking launched in v0.140. The deprecated implementation and the temporary generate_tests=true flowconfig option have now been removed.
• Fixed an issue with logical operators (&&, ||, ??) and union types
• Object rest properties (let {foo, ...rest} = obj) now retain the indexer of the object being destructured. In this example, if obj is {[string]: string}, then rest is also {[string]: string}.
• Made the parser recover gracefully in some cases when in the middle of typing, allowing language services to work better in the rest of the file
• Improved experimental cross-module autocomplete to include globals and built-in modules. Can be enabled with the autoimports=true flowconfig option.
• Fixed a bug so that the server no longer exits when merely touch-ing the .flowconfig without changing it

Notable bug fixes:

• Fixed crash on Windows and crash on Linux introduced in 0.143.0

Likely to cause new Flow errors:

• Support for Classic mode has been dropped and Types-First mode is now always enabled (Types-First has been the default mode since v0.134). The types_first and well_formed_exports flowconfig options are no longer recognized. See https://medium.com/flow-type/types-first-a-scalable-new-architecture-for-flow-3d8c7ba1d4eb/ for more about Types-First mode.
• Previously, errors in library files were sometimes being missed due to a bug. This has been fixed, which may expose errors in library files that were not previously being reported.
• Import statements are no longer allowed at the toplevel of library files. To use import statements in library files they must appear within a "declare module".

New Features:

• Added experimental support for cross-module autocompletion and code actions that fix missing import declarations. Can be enabled with the autoimports=true flowconfig option.
• Added --sharedmem-heap-size CLI flag and FLOW_SHAREDMEM_HEAP_SIZE environment variable, which can be used instead of the sharedmem.heap_size flowconfig option for setting the amount of shared memory available.

Misc:

• Added ErrorEvent library definition (thanks @kegluneq)

Likely to cause new Flow errors:

• Disallow flowing functions or inexact objects to indexed objects to improve object soundness. This can cause errors if you are passing a function or inexact objects when an indexed object is expected.
• Flow now processes imports before checking the body of a file. In some rare cases this can expose previously skipped errors due to the processing order.

Notable bug fixes:

• Fix No available version of ocaml-base-compiler satisfies the constraints error from make all-homebrew (thanks @bayandin).

• Improved inference of chained generic method calls, such as Array methods. For example, given [1, 2].map(a => a).forEach(b => b), Flow now infers that b is a number rather than any | number.
• Fixed non-termination bugs involving recursive types
• Fixed a non-termination bug involving implicit instantiation with _
• Fixed autocomplete so it no longer inserts a = in JSX attributes that already have one
• Hovering over a use of an opaque type now includes the type's documentation

Likely to cause new Flow errors:

• New generic type checking is now enabled by default, and has to be explicitly disabled with generate_tests=true in a flowconfig if desired. See https://medium.com/flow-type/flows-improved-handling-of-generic-types-b5909cc5e3c5 for more about Flow's new handling of generic types.

Notable bug fixes:

• Fixed "Could not locate flowlib files" errors when multiple users run Flow on the same machine
• Fixed autocomplete and hover for imported enum types
• Fixed autocomplete suggesting types in value positions
• Fixed a bug where correct non-boolean predicate functions were rejected

Parser:

• ESTree AST now uses Literal node for init of boolean enum members

Misc:

• Updated ShadowRoot library definition (thanks @Brianzchen)

New Features:

• Support for this annotations in functions, like function f(this: {foo: string}, param1: string): string { return this.foo; }
• The experimental.abstract_locations config option is now true by default, as it enables significant performance improvements. This option is now deprecated and will be removed in a coming version.

Notable bug fixes:

• Fixed a false positive when a bounded generic like K: string flows into $Keys<{[K]: ...}>
• Fixed a false positive when a bounded generic like K: 'literal' is checked against itself like k === 'literal'
• Fixed autocomplete inside of JSX attribute values
• Fixed autocomplete of properties of interfaces

Misc:

• Updated flow-remove-types to support this parameters
• Added SpeechRecognition definitions (thanks @ayshiff)

Likely to cause new Flow errors:

• Improved positioning of existing errors involving unions or intersections. Will not cause new errors, but may require suppressions to be moved.

Bug Fixes:

• Fixed soundness bug involving union and intersection types
• Improved performance of typechecking exact objects against $Exact

Editor Integration:

• Fixed hover and go-to-definition over the LSP when the cursor is at the end of a token
• Fixed type coverage over the LSP when using all=true (thanks @mochja)
• Fixed an issue with running the flow CLI at the same time as VS Code caused by case-insensitivity of Windows paths

Library Definitions:

• Added inputType to InputEvent (thanks @Brianzchen)
• Added intersectsNode to Range (thanks @Brianzchen)

Misc:

• Built-in library definitions are now extracted to a consistent temp directory, like /tmp/flow/flowlibs_<HASH>, to take up less space.

New Features:

• Show code actions in the IDE for some parse errors with suggested fixes.

Notable bug fixes:

• Fixed infinite recursion case involving object rest destructuring.

Library Definitions:

• Changed return type of Buffer.write to number (thanks @fedotov).

Misc:

• Saved state files generated on one platform can now be used on another platform using the same version of Flow.
• Improved saved state memory use and startup time with more efficient handling of file paths.
• Improved error message when attempting to bind a class type.
• Minimum supported MacOS version is now 10.13.

Likely to cause new Flow errors:

• Flow now raises errors when generic type variables escape out of the scope in which they were defined.

Notable bug fixes:

• Fix a race condition related to saved state and cancelable rechecks that caused internal errors of Requires_not_found or Sig_requires_not_found.

Misc:

• Added documentation to core.js builtins.
• Add optional propTypes to React.AbstractComponentStatics (thanks @brianzchen).

• Improved exhaustiveness checking in switch statements.
• Improved autocomplete results to show documentation in more cases.
• Turned the untyped-type-import lint into an error by default. In a later release, we will turn this into a regular type error instead of a lint error.
• Removed esproposal configuration options from the .flowconfig format.
• Added library definition for MediaRecorder API.
• Fixed Object.freeze to no longer incorrectly convert an inexact object into an exact object.
• Fixed handling of exported objects with spreads in types-first mode.

Likely to cause new Flow errors:

• Types-first is now the default mode, and has to be explicitly disabled with types_first=false in a flowconfig if desired. See https://medium.com/flow-type/types-first-a-scalable-new-architecture-for-flow-3d8c7ba1d4eb for more about types-first.

New Features:

• Added a file_watcher.watchman.mergebase_with flowconfig option and --file-watcher-mergebase-with CLI option to choose a tracking bookmark for Watchman to compute the mergebase against.
• Show JSDoc documentation in type declarations.

Misc:

• Improved the consistency of what operation is pointed to in error messages, to ensure they aren't dependent on the order in which constraints are generated.
• Filtered "did you mean" code actions to only send actions on code under cursor.
• Changed the return type of fileURLToPath (thanks @aaronasachimp)

Likely to cause new Flow errors:

• Improve reliability of inclusion check in strict equality conditionals.

New Features:

• Show JSDoc documentation in hover, autocomplete, and signature help.

Notable bug fixes:

• Fix a bug related to saved state that could cause crashes during initialization.
• Fix a bug related to saved state that could cause internal errors during rechecks.
• Fix crash with flow focus-check when a focused file has a syntax error.

Misc:

• Remove the null-void-addition lint now that it has been subsumed by an ordinary type error.
• Improved signature help for inlined tuple rest params.
• Enable the following language features by default, since they have reached stage 4:
  • export *
  • Nullish coalescing
  • Optional chaining
• Remove deprecated, nonstandard itemType and inlineDetail fields from the LSP completionItem implementation.
• Exit the worker processes gracefully when the main process crashes.

Likely to cause new Flow errors:

• Disallow using any-typed values type annotations. example

New Features:

• Added warnings against suppressions without error codes

Notable bug fixes:

• Fixed some crashes when Flow could not connect to Watchman

Misc:

• Fix syntax errors in README badges (thanks @jamesisaac)

• "Go to Definition" on a JSX attribute name now jumps to the prop's type.
• Improved error messages for non-strict equality checks
• Fixed a bug that prevented the use of module in ES modules when well_formed_exports is enabled.
• Fixed an issue that allowed types-first mode to be enabled (types_first=true) when using well_formed_exports.include. For types-first to function properly, the entire project's exports must be well-formed, not just specific paths.
• Fixed a similar issue so that --types-first on the command line overrides well_formed_exports=false in .flowconfig. This makes it easier to test types-first mode.
• The unsafe-addition lint now defaults to being an error. It will be converted from a lint to a type error in the future.
• Removed dynamic-export lint which does not work in types-first mode
• Improved initialization performance

New Features:

• Improved IDE get definition behavior of imported names by jumping past module.exports = ... to the actual definition.

Library Definitions:

• Made offset an optional argument for the sized Buffer read/writes (thanks @isker!)

Misc:

• Removed deprecated blacklist/whitelist aliases for config options, use includes/excludes instead (see updated docs: for Types First and flowconfig options).

Likely to cause new Flow errors:

• $Keys<...> will no longer include non-own instance properties, matching the behavior of Object.keys.

Notable bug fixes:

• Fixed an incremental rechecking issue caused by the hashes of type destructors

Misc:

• Updated the type of cast and isValid to take in optional representation type for enums
• Added missing links to Medium articles from flow.org (thanks @jamesisaac)

New Features:

• Enable LSP support for autofix exports by default.
• Added a lint rule to ensure exports named default were exported with export default syntax.
• Enabled support for JSDoc in some LSP results.

Library Definitions:

• Add parameter to MediaStreamTrack.applyConstraints()

Parser:

• Fix parsing async arrow functions with multiple type parameters

Config:

• Remove types-first flag aliases prefixed with "experimental"
• Replace well_formed_exports.whitelist with well_formed_exports.includes

Misc:

• Improvements to editor in flow.org/try, including syntax highlighting
• Fix broken links in docs
• Standardized error suppression syntax, added ability to suppress errors based on error codes

Library Definitions:

• Add KD functions
• Add onended callback to OscillatorNode
• Make 3rd parameter of node.js symlinkSync optional

• Fixed an issue where changing .flowconfig or package.json and then running flow status would get stuck in a restart loop, if using lazy mode with Watchman and Mercurial.

• Allow indexers in exact object annotations
• Fixed type-at-pos in flow.org/try
• Improved language of LSP window/showStatus responses
• Improved control flow handing in logical expressions
• Allow applying utility types to opaque types in the defining module
• Added HeadersInit and signal to Fetch API (thanks @andretshurotshka!)
• Added replace method to DOMTokenList (thanks @w01fgang!)

Publishing of flow-bin v0.125.0 failed to include the binaries. Oops!