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eslint-plugin-flowtype

Flow type linting rules for ESLint.

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eslint-plugin-flowtype

NPM version Travis build status js-canonical-style

Flow type linting rules for ESLint.

Installation

  1. Install ESLint.
  2. Install babel-eslint parser (ESLint parser does not support type annotations).
  3. Install eslint-plugin-flowtype plugin.
npm install eslint --save-dev
npm install babel-eslint --save-dev
npm install eslint-plugin-flowtype --save-dev

Configuration

  1. Set parser property to babel-eslint.
  2. Add plugins section and specify eslint-plugin-flowtype as a plugin.
  3. Enable rules.
{
  "parser": "babel-eslint",
  "plugins": [
    "flowtype"
  ],
  "rules": {
    "flowtype/boolean-style": [
      2,
      "boolean"
    ],
    "flowtype/define-flow-type": 1,
    "flowtype/delimiter-dangle": [
      2,
      "never"
    ],
    "flowtype/generic-spacing": [
      2,
      "never"
    ],
    "flowtype/no-primitive-constructor-types": 2,
    "flowtype/no-types-missing-file-annotation": 2,
    "flowtype/no-weak-types": 2,
    "flowtype/object-type-delimiter": [
      2,
      "comma"
    ],
    "flowtype/require-parameter-type": 2,
    "flowtype/require-return-type": [
      2,
      "always",
      {
        "annotateUndefined": "never"
      }
    ],
    "flowtype/require-valid-file-annotation": 2,
    "flowtype/semi": [
      2,
      "always"
    ],
    "flowtype/space-after-type-colon": [
      2,
      "always"
    ],
    "flowtype/space-before-generic-bracket": [
      2,
      "never"
    ],
    "flowtype/space-before-type-colon": [
      2,
      "never"
    ],
    "flowtype/type-id-match": [
      2,
      "^([A-Z][a-z0-9]+)+Type$"
    ],
    "flowtype/union-intersection-spacing": [
      2,
      "always"
    ],
    "flowtype/use-flow-type": 1,
    "flowtype/valid-syntax": 1
  },
  "settings": {
    "flowtype": {
      "onlyFilesWithFlowAnnotation": false
    }
  }
}

Shareable configurations

Recommended

This plugin exports a recommended configuration that enforces Flow type good practices.

To enable this configuration use the extends property in your .eslintrc config file:

{
  "extends": [
    "plugin:flowtype/recommended"
  ],
  "plugins": [
    "flowtype"
  ]
}

See ESLint documentation for more information about extending configuration files.

Settings

onlyFilesWithFlowAnnotation

When true, only checks files with a @flow annotation in the first comment.

{
  "settings": {
    "flowtype": {
      "onlyFilesWithFlowAnnotation": true
    }
  }
}

Rules

boolean-style

The --fix option on the command line automatically fixes problems reported by this rule.

Enforces a particular style for boolean type annotations. This rule takes one argument.

If it is 'boolean' then a problem is raised when using bool instead of boolean.

If it is 'bool' then a problem is raised when using boolean instead of bool.

The default value is 'boolean'.

The following patterns are considered problems:

type X = bool
// Message: Use "boolean", not "bool"

// Options: ["boolean"]
type X = bool
// Message: Use "boolean", not "bool"

// Options: ["bool"]
type X = boolean
// Message: Use "bool", not "boolean"

The following patterns are not considered problems:

type X = boolean

// Options: ["boolean"]
type X = boolean

// Options: ["bool"]
type X = bool

// Options: ["boolean"]
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
type X = bool

define-flow-type

Marks Flow type identifiers as defined.

Used to suppress no-undef reporting of type identifiers.

The following patterns are not considered problems:

var a: AType
// Additional rules: {"no-undef":2}

var a: AType; var b: AType
// Additional rules: {"no-undef":2}

var a; (a: AType)
// Additional rules: {"no-undef":2}

var a: AType<BType>
// Additional rules: {"no-undef":2}

type A = AType
// Additional rules: {"no-undef":2}

declare type A = number
// Additional rules: {"no-undef":2}

opaque type A = AType
// Additional rules: {"no-undef":2}

function f(a: AType) {}
// Additional rules: {"no-undef":2}

function f(a: AType.a) {}
// Additional rules: {"no-undef":2}

function f(a: AType.a.b) {}
// Additional rules: {"no-undef":2}

function f(a): AType {}; var a: AType
// Additional rules: {"no-undef":2}

function f(a): AType {}
// Additional rules: {"no-undef":2}

class C { a: AType }
// Additional rules: {"no-undef":2}

class C { a: AType.a }
// Additional rules: {"no-undef":2}

class C { a: AType.a.b }
// Additional rules: {"no-undef":2}

class C implements AType {}
// Additional rules: {"no-undef":2}

interface AType {}
// Additional rules: {"no-undef":2}

declare interface A {}
// Additional rules: {"no-undef":2}

({ a: ({b() {}}: AType) })
// Additional rules: {"no-undef":2}

type X = {Y<AType>(): BType}
// Additional rules: {"no-undef":2}

interface AType<BType> {}
// Additional rules: {"no-undef":2}

var a: AType
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

var a: AType; var b: AType
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

var a; (a: AType)
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

var a: AType<BType>
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

type A = AType
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

declare type A = number
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

opaque type A = AType
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

function f(a: AType) {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

function f(a: AType.a) {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

function f(a: AType.a.b) {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

function f(a): AType {}; var a: AType
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

function f(a): AType {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

class C { a: AType }
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

class C { a: AType.a }
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

class C { a: AType.a.b }
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

class C implements AType {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

interface AType {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

declare interface A {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

({ a: ({b() {}}: AType) })
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

type X = {Y<AType>(): BType}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

interface AType<BType> {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}

delimiter-dangle

The --fix option on the command line automatically fixes problems reported by this rule.

Enforces consistent use of trailing commas in Object and Tuple annotations.

This rule takes one argument which mirrors ESLint's default comma-dangle rule.

If it is 'never' then a problem is raised when there is a trailing comma.

If it is 'always' then a problem is raised when there is no trailing comma.

If it is 'always-multiline' then a problem is raised when there is no trailing comma on a multi-line definition, or there is a trailing comma on a single-line definition.

If it is 'only-multiline' then a problem is raised when there is a trailing comma on a single-line definition. It allows, but does not enforce, trailing commas on multi-line definitions.

The default value is 'never'.

The following patterns are considered problems:

type X = { foo: string, }
// Message: Unexpected trailing delimiter

// Options: ["never"]
type X = { foo: string, }
// Message: Unexpected trailing delimiter

// Options: ["never"]
type X = { foo: string; }
// Message: Unexpected trailing delimiter

// Options: ["never"]
type X = {
foo: string,
}
// Message: Unexpected trailing delimiter

// Options: ["always"]
type X = { foo: string }
// Message: Missing trailing delimiter

// Options: ["always"]
type X = {
foo: string
}
// Message: Missing trailing delimiter

// Options: ["always-multiline"]
type X = { foo: string, }
// Message: Unexpected trailing delimiter

// Options: ["always-multiline"]
type X = {
foo: string
}
// Message: Missing trailing delimiter

// Options: ["only-multiline"]
type X = { foo: string; }
// Message: Unexpected trailing delimiter

// Options: ["never"]
type X = { [key: string]: number, }
// Message: Unexpected trailing delimiter

// Options: ["always"]
type X = { [key: string]: number }
// Message: Missing trailing delimiter

// Options: ["always-multiline"]
type X = { [key: string]: number, }
// Message: Unexpected trailing delimiter

// Options: ["always-multiline"]
type X = {
[key: string]: number
}
// Message: Missing trailing delimiter

// Options: ["only-multiline"]
type X = { [key: string]: number; }
// Message: Unexpected trailing delimiter

// Options: ["never"]
type X = { [key: string]: number, foo: string, }
// Message: Unexpected trailing delimiter

// Options: ["never"]
type X = {
[key: string]: number,
foo: string,
}
// Message: Unexpected trailing delimiter

// Options: ["never"]
type X = {
[key: string]: number,
aReallyLongPropertyNameHere: string,
}
// Message: Unexpected trailing delimiter

// Options: ["always"]
type X = { [key: string]: number, foo: string }
// Message: Missing trailing delimiter

// Options: ["always"]
type X = {
[key: string]: number;
foo: string
}
// Message: Missing trailing delimiter

// Options: ["always-multiline"]
type X = { [key: string]: number, foo: string, }
// Message: Unexpected trailing delimiter

// Options: ["always-multiline"]
type X = {
[key: string]: number,
foo: string
}
// Message: Missing trailing delimiter

// Options: ["only-multiline"]
type X = { [key: string]: number, foo: string, }
// Message: Unexpected trailing delimiter

// Options: ["never"]
type X = { foo: string, [key: string]: number, }
// Message: Unexpected trailing delimiter

// Options: ["never"]
type X = {
foo: string,
[key: string]: number,
}
// Message: Unexpected trailing delimiter

// Options: ["never"]
type X = {
aReallyLongPropertyNameHere: string,
[key: string]: number,
}
// Message: Unexpected trailing delimiter

// Options: ["always"]
type X = { foo: string, [key: string]: number }
// Message: Missing trailing delimiter

// Options: ["always"]
type X = { foo: string; [key: string]: number }
// Message: Missing trailing delimiter

// Options: ["always-multiline"]
type X = { foo: string, [key: string]: number; }
// Message: Unexpected trailing delimiter

// Options: ["always-multiline"]
type X = {
foo: string,
[key: string]: number
}
// Message: Missing trailing delimiter

// Options: ["only-multiline"]
type X = { foo: string, [key: string]: number; }
// Message: Unexpected trailing delimiter

type X = [string, number,]
// Message: Unexpected trailing delimiter

// Options: ["never"]
type X = [string, number,]
// Message: Unexpected trailing delimiter

// Options: ["never"]
type X = [
string,
number,
]
// Message: Unexpected trailing delimiter

// Options: ["always"]
type X = [string, number]
// Message: Missing trailing delimiter

// Options: ["always"]
type X = [
string,
number
]
// Message: Missing trailing delimiter

// Options: ["always-multiline"]
type X = [string, number,]
// Message: Unexpected trailing delimiter

// Options: ["always-multiline"]
type X = [
foo, string
]
// Message: Missing trailing delimiter

// Options: ["only-multiline"]
type X = [ number, string, ]
// Message: Unexpected trailing delimiter

The following patterns are not considered problems:

type X = { foo: string }

// Options: ["never"]
type X = { foo: string }

// Options: ["always"]
type X = { foo: string, }

// Options: ["always"]
type X = { foo: string; }

// Options: ["never"]
type X = {
foo: string
}

// Options: ["always"]
type X = {
foo: string,
}

// Options: ["always-multiline"]
type X = { foo: string }

// Options: ["always-multiline"]
type X = {
foo: string,
}

// Options: ["always-multiline"]
type X = {
foo: string;
}

// Options: ["only-multiline"]
type X = { foo: string }

// Options: ["only-multiline"]
type X = {
foo: string
}

// Options: ["only-multiline"]
type X = {
foo: string,
}

// Options: ["only-multiline"]
type X = {
foo: string;
}

// Options: ["never"]
type X = {}

// Options: ["always"]
type X = {}

// Options: ["always-multiline"]
type X = {}

// Options: ["only-multiline"]
type X = {}

// Options: ["never"]
type X = { [key: string]: number }

// Options: ["always"]
type X = { [key: string]: number, }

// Options: ["always"]
type X = { [key: string]: number; }

// Options: ["always-multiline"]
type X = { [key: string]: number }

// Options: ["always-multiline"]
type X = {
[key: string]: number,
}

// Options: ["only-multiline"]
type X = {
[key: string]: number,
}

// Options: ["only-multiline"]
type X = {
[key: string]: number
}

// Options: ["only-multiline"]
type X = { [key: string]: number }

// Options: ["never"]
type X = { [key: string]: number, foo: string }

// Options: ["always"]
type X = { [key: string]: number, foo: string, }

// Options: ["always"]
type X = { [key: string]: number; foo: string; }

// Options: ["always-multiline"]
type X = { [key: string]: number, foo: string }

// Options: ["always-multiline"]
type X = {
[key: string]: number,
foo: string,
}

// Options: ["only-multiline"]
type X = {
[key: string]: number,
foo: string,
}

// Options: ["only-multiline"]
type X = {
[key: string]: number;
foo: string
}

// Options: ["only-multiline"]
type X = { [key: string]: number, foo: string }

// Options: ["never"]
type X = { foo: string, [key: string]: number }

// Options: ["always"]
type X = { foo: string, [key: string]: number, }

// Options: ["always"]
type X = { foo: string; [key: string]: number; }

// Options: ["always-multiline"]
type X = { foo: string, [key: string]: number }

// Options: ["always-multiline"]
type X = {
foo: string,
[key: string]: number,
}

// Options: ["only-multiline"]
type X = {
foo: string,
[key: string]: number,
}

// Options: ["only-multiline"]
type X = {
foo: string;
[key: string]: number
}

// Options: ["only-multiline"]
type X = { foo: string, [key: string]: number }

type X = [string, number]

// Options: ["never"]
type X = [string, number]

// Options: ["never"]
type X = [
string,
number
]

// Options: ["always"]
type X = [string, number,]

// Options: ["always"]
type X = [
string,
number,
]

// Options: ["always-multiline"]
type X = [ foo, string ]

// Options: ["always-multiline"]
type X = [
foo, string,
]

// Options: ["only-multiline"]
type X = [ number, string ]

// Options: ["only-multiline"]
type X = [
number,
string
]

// Options: ["only-multiline"]
type X = [
number,
string,
]

// Options: ["never"]
type X = []

// Options: ["always"]
type X = []

// Options: ["always-multiline"]
type X = []

// Options: ["only-multiline"]
type X = []

generic-spacing

The --fix option on the command line automatically fixes problems reported by this rule.

Enforces consistent spacing within generic type annotation parameters.

This rule takes one argument. If it is 'never' then a problem is raised when there is a space surrounding the generic type parameters. If it is 'always' then a problem is raised when there is no space surrounding the generic type parameters.

The default value is 'never'.

The following patterns are considered problems:

type X = Promise< string>
// Message: There must be no space at start of "Promise" generic type annotation

// Options: ["never"]
type X = Promise<  string>
// Message: There must be no space at start of "Promise" generic type annotation

type X = FooBar<string >
// Message: There must be no space at end of "FooBar" generic type annotation

type X = Promise< string >
// Message: There must be no space at start of "Promise" generic type annotation
// Message: There must be no space at end of "Promise" generic type annotation

type X = Promise< (foo), bar, (((baz))) >
// Message: There must be no space at start of "Promise" generic type annotation
// Message: There must be no space at end of "Promise" generic type annotation

// Options: ["always"]
type X = Promise<string >
// Message: There must be a space at start of "Promise" generic type annotation

// Options: ["always"]
type X = FooBar< string>
// Message: There must be a space at end of "FooBar" generic type annotation

// Options: ["always"]
type X = Promise<string>
// Message: There must be a space at start of "Promise" generic type annotation
// Message: There must be a space at end of "Promise" generic type annotation

// Options: ["always"]
type X = Promise<(foo), bar, (((baz)))>
// Message: There must be a space at start of "Promise" generic type annotation
// Message: There must be a space at end of "Promise" generic type annotation

// Options: ["always"]
type X = FooBar<  string >
// Message: There must be one space at start of "FooBar" generic type annotation

// Options: ["always"]
type X = FooBar< string  >
// Message: There must be one space at end of "FooBar" generic type annotation

// Options: ["always"]
type X = Promise<  (foo), bar, (((baz)))  >
// Message: There must be one space at start of "Promise" generic type annotation
// Message: There must be one space at end of "Promise" generic type annotation

The following patterns are not considered problems:

type X = Promise<string>

type X = Promise<(string)>

type X = Promise<(foo), bar, (((baz)))>

// Options: ["always"]
type X = Promise< string >

// Options: ["always"]
type X = Promise< (string) >

// Options: ["always"]
type X = Promise< (foo), bar, (((baz))) >

no-dupe-keys

Checks for duplicate properties in Object annotations.

This rule mirrors ESLint's no-dupe-keys rule.

{
    "rules": {
        "flowtype/no-dupe-keys": 2
    }
}

The following patterns are considered problems:

type f = { a: number, b: string, a: number }
// Message: Duplicate property.

type f = { a: number, b: string, a: string }
// Message: Duplicate property.

type f = { get(key: "a"): string, get(key: "a"): string }
// Message: Duplicate property.

type f = { get(key: 1): string, get(key: 1): string }
// Message: Duplicate property.

type f = { get(key: 1.1): string, get(key: 1.1): string }
// Message: Duplicate property.

type f = { get(key: true): string, get(key: true): string }
// Message: Duplicate property.

type f = { get(key: {a: 1}): string, get(key: {a: 1}):string }
// Message: Duplicate property.

var a = "a"; type f = { get(key: a): string, get(key: a): string }
// Message: Duplicate property.

var b = 1; type f = { get(key: b): string, get(key: b): string }
// Message: Duplicate property.

var c = true; type f = { get(key: c): string, get(key: c): string }
// Message: Duplicate property.

var d = {}; type f = { get(key: d): string, get(key: d): string }
// Message: Duplicate property.

var e = []; type f = { get(key: e): string, get(key: e): string }
// Message: Duplicate property.

var e = [1, "a"]; type f = { get(key: e): string, get(key: e): string }
// Message: Duplicate property.

function fn() {}; type f = { get(key: fn): string, get(key: fn): string }
// Message: Duplicate property.

The following patterns are not considered problems:

type FooType = { a: number, b: string, c: number }

// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
type FooType = { a: number, b: string, a: number }

type f = { get(key: "a"): string, get(key: "b"): string }

type f = { get(key: 1): string, get(key: 2): string }

type f = { get(key: 1.1): string, get(key: 1.2): string }

type f = { get(key: true): string, get(key: false): string }

type f = { get(key: ["a", 1]): string, get(key: ["a", 2]): string }

type f = { get(key: ["a", ["b", 1]]): string, get(key: ["a", ["b", 2]]): string }

type f = { a: number, b: string, c: number }

type f = { get(key: "a"): string, get(key: "b"): string }

type f = { get(key: "a"): string, get(key: "a", key2: "b"): string }

type f = { get(key: "a"): string, get(key: 1): string }

type f = { get(key: { a: 1 }): string, get(key: { a: 2 }): string}

var a = {}; var b = {}; type f = { get(key: a): string, get(key: b): string }

var a = 1; var b = 1; type f = { get(key: a): string, get(key: b): string }

no-flow-fix-me-comments

Disallows $FlowFixMe comment suppressions.

This is especially useful as a warning to ensure instances of $FlowFixMe in your codebase get fixed over time.

Options

This rule takes an optional RegExp that comments a text RegExp that makes the supression valid.

{
    "rules": {
        "flowtype/no-flow-fix-me-comments": [
            1,
            "TODO\s+[0-9]+"
        ]
    }
}

no-mutable-array

The --fix option on the command line automatically fixes problems reported by this rule.

Requires use of $ReadOnlyArray instead of just Array or array shorthand notation. $ReadOnlyArray is immutable array collection type and the superclass of Array and tuple types in Flow. Use of $ReadOnlyArray instead of Array can solve some problems in typing with Flow (e.g., 1, 2).

General reasons for using immutable data structures:

  • They are simpler to construct, test, and use
  • They help to avoid temporal coupling
  • Their usage is side-effect free (no defensive copies)
  • Identity mutability problem is avoided
  • They always have failure atomicity
  • They are much easier to cache

The following patterns are considered problems:

type X = Array<string>
// Message: Use "$ReadOnlyArray" instead of "Array"

type X = string[]
// Message: Use "$ReadOnlyArray" instead of array shorthand notation

The following patterns are not considered problems:

type X = $ReadOnlyArray<string>

no-primitive-constructor-types

Disallows use of primitive constructors as types, such as Boolean, Number and String. See more.

{
    "rules": {
        "flowtype/no-primitive-constructor-types": 2
    }
}

The following patterns are considered problems:

type x = Number
// Message: Unexpected use of Number constructor type.

type x = String
// Message: Unexpected use of String constructor type.

type x = Boolean
// Message: Unexpected use of Boolean constructor type.

type x = { a: Number }
// Message: Unexpected use of Number constructor type.

type x = { a: String }
// Message: Unexpected use of String constructor type.

type x = { a: Boolean }
// Message: Unexpected use of Boolean constructor type.

(x: Number) => {}
// Message: Unexpected use of Number constructor type.

(x: String) => {}
// Message: Unexpected use of String constructor type.

(x: Boolean) => {}
// Message: Unexpected use of Boolean constructor type.

The following patterns are not considered problems:

type x = number

type x = string

type x = boolean

type x = { a: number }

type x = { a: string }

type x = { a: boolean }

(x: number) => {}

(x: string) => {}

(x: boolean) => {}

type x = MyNumber

type x = MyString

type x = MyBoolean

no-types-missing-file-annotation

Disallows Flow type imports, aliases, and annotations in files missing a valid Flow file declaration (or a @noflow annotation).

{
    "rules": {
        "flowtype/no-types-missing-file-annotation": 2
    }
}

The following patterns are considered problems:

const x: number = 42;
// Message: Type annotations require valid Flow declaration.

type FooType = number;
// Message: Type aliases require valid Flow declaration.

import type A from "a"
// Message: Type imports require valid Flow declaration.

import type {A} from "a"
// Message: Type imports require valid Flow declaration.

import {type A} from "a"
// Message: Type imports require valid Flow declaration.

export type {A} from "a"
// Message: Type exports require valid Flow declaration.

function t<T>(): T{}
// Message: Type annotations require valid Flow declaration.

// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
const x: number = 42;
// Message: Type annotations require valid Flow declaration.

The following patterns are not considered problems:

// @flow
const x: number = 42;

/* @flow weak */
type FooType = number;

/* @noflow */
type FooType = number;

/* @noflow */
import type A from "a"

/* @noflow */
import {type A} from "a"

/* @noflow */
export type {A} from "a"

// an unrelated comment
// @flow
export type {A} from "a"

no-unused-expressions

An extension of ESLint's no-unused-expressions. This rule ignores type cast expressions, but otherwise behaves the same as ESLint's no-unused-expressions.

Bare type casts are useful, for example to assert the exhaustiveness of a switch:

type Action
  = { type: 'FOO', doFoo: (_: number) => void }
  | { type: 'BAR', doBar: (_: string) => void };

type State = { foo: number, bar: string };

function runFooBar(action: Action, state: State): void {
  switch (action.type) {
    case 'FOO':
      doFoo(state.foo);
      break;
    case 'BAR':
      doBar(state.bar);
      break;
    default:
      (action: empty);  // type error when `Action` is extended with new types
      console.error(`Impossible action: ${action.toString()}`);
  }
}

This rule takes the same arguments as ESLint's no-unused-expressions. See that rule's documentation for details.

The following patterns are considered problems:

foo + 1
// Message: Expected an assignment or function call and instead saw an expression.

The following patterns are not considered problems:

(foo: number)

no-weak-types

Warns against weak type annotations any, Object and Function. These types can cause flow to silently skip over portions of your code, which would have otherwise caused type errors.

This rule optionally takes one argument, an object to configure which type warnings to enable. By default, all of the warnings are enabled. e.g. to disable the any warning (allowing it to exist in your code), while continuing to warn about Object and Function:

{
    "rules": {
        "flowtype/no-weak-types": [2, {
            "any": false,
            "Object": true,
            "Function": true
        }]
    }
}

// or, the following is equivalent as default is true:

{
    "rules": {
        "flowtype/no-weak-types": [2, {
            "any": false
        }]
    }
}

The following patterns are considered problems:

function foo(thing): any {}
// Message: Unexpected use of weak type "any"

function foo(thing): Promise<any> {}
// Message: Unexpected use of weak type "any"

function foo(thing): Promise<Promise<any>> {}
// Message: Unexpected use of weak type "any"

function foo(thing): Object {}
// Message: Unexpected use of weak type "Object"

function foo(thing): Promise<Object> {}
// Message: Unexpected use of weak type "Object"

function foo(thing): Promise<Promise<Object>> {}
// Message: Unexpected use of weak type "Object"

function foo(thing): Function {}
// Message: Unexpected use of weak type "Function"

function foo(thing): Promise<Function> {}
// Message: Unexpected use of weak type "Function"

function foo(thing): Promise<Promise<Function>> {}
// Message: Unexpected use of weak type "Function"

(foo: any) => {}
// Message: Unexpected use of weak type "any"

(foo: Function) => {}
// Message: Unexpected use of weak type "Function"

(foo?: any) => {}
// Message: Unexpected use of weak type "any"

(foo?: Function) => {}
// Message: Unexpected use of weak type "Function"

(foo: { a: any }) => {}
// Message: Unexpected use of weak type "any"

(foo: { a: Object }) => {}
// Message: Unexpected use of weak type "Object"

(foo: any[]) => {}
// Message: Unexpected use of weak type "any"

type Foo = any
// Message: Unexpected use of weak type "any"

type Foo = Function
// Message: Unexpected use of weak type "Function"

type Foo = { a: any }
// Message: Unexpected use of weak type "any"

type Foo = { a: Object }
// Message: Unexpected use of weak type "Object"

type Foo = { (a: Object): string }
// Message: Unexpected use of weak type "Object"

type Foo = { (a: string): Function }
// Message: Unexpected use of weak type "Function"

function foo(thing: any) {}
// Message: Unexpected use of weak type "any"

function foo(thing: Object) {}
// Message: Unexpected use of weak type "Object"

var foo: Function
// Message: Unexpected use of weak type "Function"

var foo: Object
// Message: Unexpected use of weak type "Object"

class Foo { props: any }
// Message: Unexpected use of weak type "any"

class Foo { props: Object }
// Message: Unexpected use of weak type "Object"

var foo: any
// Message: Unexpected use of weak type "any"

// Options: [{"Function":false}]
type X = any; type Y = Function; type Z = Object
// Message: Unexpected use of weak type "any"
// Message: Unexpected use of weak type "Object"

// Options: [{"Object":false,"any":false}]
type X = any; type Y = Function; type Z = Object
// Message: Unexpected use of weak type "Function"

The following patterns are not considered problems:

function foo(thing): string {}

function foo(thing): Promise<string> {}

function foo(thing): Promise<Promise<string>> {}

(foo?: string) => {}

(foo: ?string) => {}

(foo: { a: string }) => {}

(foo: { a: ?string }) => {}

(foo: string[]) => {}

type Foo = string

type Foo = { a: string }

type Foo = { (a: string): string }

function foo(thing: string) {}

var foo: string

class Foo { props: string }

// Options: [{"Object":false,"any":false}]
type X = any; type Y = Object

// Options: [{"Function":false}]
type X = Function

// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
function foo(thing): Function {}

object-type-delimiter

The --fix option on the command line automatically fixes problems reported by this rule.

Enforces consistent separators between properties in Flow object types.

This rule takes one argument.

If it is 'comma' then a problem is raised when using ; as a separator.

If it is 'semicolon' then a problem is raised when using , as a separator.

The default value is 'comma'.

This rule is ported from babel/flow-object-type, however the default option was changed.

The following patterns are considered problems:

// Options: ["semicolon"]
type Foo = { a: Foo, b: Bar }
// Message: Prefer semicolons to commas in object and class types

// Options: ["comma"]
type Foo = { a: Foo; b: Bar }
// Message: Prefer commas to semicolons in object and class types

// Options: ["semicolon"]
type Foo = { [a: string]: Foo, [b: string]: Bar }
// Message: Prefer semicolons to commas in object and class types

// Options: ["comma"]
type Foo = { [a: string]: Foo; [b: string]: Bar }
// Message: Prefer commas to semicolons in object and class types

// Options: ["semicolon"]
type Foo = { (): Foo, (): Bar }
// Message: Prefer semicolons to commas in object and class types

// Options: ["comma"]
type Foo = { (): Foo; (): Bar }
// Message: Prefer commas to semicolons in object and class types

// Options: ["semicolon"]
declare class Foo { a: Foo, }
// Message: Prefer semicolons to commas in object and class types

// Options: ["comma"]
declare class Foo { a: Foo; }
// Message: Prefer commas to semicolons in object and class types

// Options: ["semicolon"]
declare class Foo { [a: string]: Foo, }
// Message: Prefer semicolons to commas in object and class types

// Options: ["comma"]
declare class Foo { a: Foo; }
// Message: Prefer commas to semicolons in object and class types

// Options: ["semicolon"]
declare class Foo { (): Foo, }
// Message: Prefer semicolons to commas in object and class types

// Options: ["comma"]
declare class Foo { (): Foo; }
// Message: Prefer commas to semicolons in object and class types

// Options: ["semicolon"]
declare class Foo { static (): Foo, }
// Message: Prefer semicolons to commas in object and class types

// Options: ["comma"]
declare class Foo { static (): Foo; }
// Message: Prefer commas to semicolons in object and class types

The following patterns are not considered problems:

// Options: ["semicolon"]
type Foo = { a: Foo; b: Bar }

// Options: ["comma"]
type Foo = { a: Foo, b: Bar }

// Options: ["semicolon"]
type Foo = { [a: string]: Foo; [b: string]: Bar }

// Options: ["comma"]
type Foo = { [a: string]: Foo, [b: string]: Bar }

// Options: ["semicolon"]
type Foo = { (): Foo; (): Bar }

// Options: ["comma"]
type Foo = { (): Foo, (): Bar }

type Foo = { a: Foo, b: Bar }

type Foo = { [a: string]: Foo, [b: string]: Bar }

type Foo = { (): Foo, (): Bar }

// Options: ["semicolon"]
declare class Foo { a: Foo; }

// Options: ["comma"]
declare class Foo { a: Foo, }

// Options: ["semicolon"]
declare class Foo { [a: string]: Foo; }

// Options: ["comma"]
declare class Foo { [a: string]: Foo, }

// Options: ["semicolon"]
declare class Foo { (): Foo; }

// Options: ["comma"]
declare class Foo { (): Foo, }

// Options: ["semicolon"]
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
type Foo = { a: Foo, b: Bar }

require-exact-type

This rule enforces exact object types.

Options

The rule has one string option:

  • "always" (default): Report all object type definitions that aren't exact.
  • "never": Report all object type definitions that are exact.
{
  "rules": {
    "flowtype/require-exact-type": [
      2,
      "always"
    ]
  }
}

{
  "rules": {
    "flowtype/require-exact-type": [
      2,
      "never"
    ]
  }
}

The following patterns are considered problems:

type foo = {};
// Message: Type identifier 'foo' must be exact.

type foo = { bar: string };
// Message: Type identifier 'foo' must be exact.

// Options: ["always"]
type foo = {};
// Message: Type identifier 'foo' must be exact.

// Options: ["always"]
type foo = { bar: string };
// Message: Type identifier 'foo' must be exact.

// Options: ["never"]
type foo = {| |};
// Message: Type identifier 'foo' must not be exact.

// Options: ["never"]
type foo = {| bar: string |};
// Message: Type identifier 'foo' must not be exact.

The following patterns are not considered problems:

type foo = {| |};

type foo = {| bar: string |};

type foo = number;

// Options: ["always"]
type foo = {| |};

// Options: ["always"]
type foo = {| bar: string |};

// Options: ["always"]
type foo = number;

// Options: ["never"]
type foo = { };

// Options: ["never"]
type foo = { bar: string };

// Options: ["never"]
type foo = number;

require-parameter-type

Requires that all function parameters have type annotations.

Options

You can skip all arrow functions by providing the excludeArrowFunctions option with true.

Alternatively, you can want to exclude only concise arrow functions (e.g. x => x * 2). Provide excludeArrowFunctions with expressionsOnly for this.

{
    "rules": {
        "flowtype/require-parameter-type": [
            2,
            {
              "excludeArrowFunctions": true
            }
        ]
    }
}

{
    "rules": {
        "flowtype/require-parameter-type": [
            2,
            {
              "excludeArrowFunctions": "expressionsOnly"
            }
        ]
    }
}

You can exclude parameters that match a certain regex by using excludeParameterMatch.

{
    "rules": {
        "flowtype/require-parameter-type": [
            2,
            {
              "excludeParameterMatch": "^_"
            }
        ]
    }
}

This excludes all parameters that start with an underscore (_). The default pattern is a^, which doesn't match anything, i.e., all parameters are checked.

The following patterns are considered problems:

(foo) => {}
// Message: Missing "foo" parameter type annotation.

function x(foo) {}
// Message: Missing "foo" parameter type annotation.

// Options: [{"excludeArrowFunctions":true}]
function x(foo) {}
// Message: Missing "foo" parameter type annotation.

(foo = 'FOO') => {}
// Message: Missing "foo" parameter type annotation.

(...foo) => {}
// Message: Missing "foo" parameter type annotation.

({foo}) => {}
// Message: Missing "{foo}" parameter type annotation.

([foo]) => {}
// Message: Missing "[foo]" parameter type annotation.

({foo = 1} = {}) => {}
// Message: Missing "{foo = 1}" parameter type annotation.

// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
// @flow
(foo) => {}
// Message: Missing "foo" parameter type annotation.

// Options: [{"excludeArrowFunctions":"expressionsOnly"}]
(foo) => {}
// Message: Missing "foo" parameter type annotation.

// Options: [{"excludeArrowFunctions":"expressionsOnly"}]
function x(foo) {}
// Message: Missing "foo" parameter type annotation.

// Options: [{"excludeParameterMatch":"^_"}]
(_foo: number, bar) => {}
// Message: Missing "bar" parameter type annotation.

// Options: [{"excludeParameterMatch":"^_"}]
(_foo, bar) => {}
// Message: Missing "bar" parameter type annotation.

The following patterns are not considered problems:

(foo: string) => {}

(foo: string = 'FOO') => {}

(...foo: string) => {}

({foo}: {foo: string}) => {}

([foo]: Array) => {}

// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
(foo) => {}

// Options: [{"excludeArrowFunctions":true}]
(foo) => {}

// Options: [{"excludeArrowFunctions":"expressionsOnly"}]
(foo) => 3

// Options: [{"excludeParameterMatch":"^_"}]
(_foo, bar: string) => {}

// Options: [{"excludeParameterMatch":"^_"}]
(_foo: number, bar: string) => {}

// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
(foo) => {}

require-return-type

Requires that functions have return type annotation.

Options

You can skip all arrow functions by providing the excludeArrowFunctions option with true.

Alternatively, you can exclude a concise arrow function (e.g. () => 2). Provide excludeArrowFunctions with expressionsOnly for this.

{
    "rules": {
        "flowtype/require-return-type": [
            2,
            "always",
            {
              "excludeArrowFunctions": true
            }
        ]
    }
}

{
    "rules": {
        "flowtype/require-return-type": [
            2,
            "always",
            {
              "excludeArrowFunctions": "expressionsOnly"
            }
        ]
    }
}

You can exclude or include specific tests with the includeOnlyMatching and excludeMatching rules.

{
    "rules": {
        "flowtype/require-return-type": [
            2,
            "always",
            {
              "includeOnlyMatching": [
                  "^F.*",
                  "Ba(r|z)"
              ]
            }
        ]
    }
}

{
    "rules": {
        "flowtype/require-return-type": [
            2,
            "always",
            {
              "excludeMatching": [
                  "^F.*",
                  "Ba(r|z)"
              ]
            }
        ]
    }
}

Both rules take an array that can contain either strings or valid RegExp statements.

The following patterns are considered problems:

(foo) => { return "foo"; }
// Message: Missing return type annotation.

// Options: ["always"]
(foo) => { return "foo"; }
// Message: Missing return type annotation.

// Options: ["always"]
(foo) => "foo"
// Message: Missing return type annotation.

(foo) => ({})
// Message: Missing return type annotation.

(foo): undefined => { return; }
// Message: Must not annotate undefined return type.

(foo): void => { return; }
// Message: Must not annotate undefined return type.

(foo): undefined => { return undefined; }
// Message: Must not annotate undefined return type.

(foo): void => { return void 0; }
// Message: Must not annotate undefined return type.

// Options: ["always",{"annotateUndefined":"never"}]
(foo): undefined => { return; }
// Message: Must not annotate undefined return type.

// Options: ["always",{"annotateUndefined":"never"}]
(foo): void => { return; }
// Message: Must not annotate undefined return type.

// Options: ["always",{"annotateUndefined":"always"}]
(foo) => { return; }
// Message: Must annotate undefined return type.

// Options: ["always",{"annotateUndefined":"never"}]
(foo): undefined => { return undefined; }
// Message: Must not annotate undefined return type.

// Options: ["always",{"annotateUndefined":"always"}]
(foo) => { return undefined; }
// Message: Must annotate undefined return type.

// Options: ["always",{"annotateUndefined":"always"}]
(foo) => { return void 0; }
// Message: Must annotate undefined return type.

// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
// @flow
(foo) => { return 1; }
// Message: Missing return type annotation.

// Options: ["always",{"annotateUndefined":"always"}]
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
// @flow
 (foo) => { return undefined; }
// Message: Must annotate undefined return type.

// Options: ["always"]
async () => { return 2; }
// Message: Missing return type annotation.

// Options: ["always",{"annotateUndefined":"always"}]
async () => {}
// Message: Missing return type annotation.

// Options: ["always",{"annotateUndefined":"always"}]
async function x() {}
// Message: Missing return type annotation.

// Options: ["always",{"annotateUndefined":"always"}]
class Test { constructor() { } }
// Message: Must annotate undefined return type.

class Test { foo() { return 42; } }
// Message: Missing return type annotation.

class Test { foo = () => { return 42; } }
// Message: Missing return type annotation.

class Test { foo = () => 42; }
// Message: Missing return type annotation.

// Options: ["always"]
async () => { return; }
// Message: Missing return type annotation.

// Options: ["always"]
function* x() {}
// Message: Missing return type annotation.

// Options: ["always",{"excludeArrowFunctions":"expressionsOnly"}]
() => { return 3; }
// Message: Missing return type annotation.

// Options: ["always",{"excludeArrowFunctions":"expressionsOnly"}]
async () => { return 4; }
// Message: Missing return type annotation.

// Options: ["always",{"includeOnlyMatching":["bar"]}]
function foo() { return 42; }
function bar() { return 42; }
// Message: Missing return type annotation.

// Options: ["always",{"includeOnlyMatching":["bar"]}]
const foo = () => { return 42; };
const bar = () => { return 42; }
// Message: Missing return type annotation.

The following patterns are not considered problems:

return;

(foo): string => {}

// Options: ["always"]
(foo): string => {}

(foo) => { return; }

(foo): Object => ( {} )

(foo) => { return undefined; }

(foo) => { return void 0; }

// Options: ["always",{"annotateUndefined":"always"}]
(foo): undefined => { return; }

// Options: ["always",{"annotateUndefined":"always"}]
(foo): void => { return; }

// Options: ["always",{"annotateUndefined":"never"}]
(foo) => { return; }

// Options: ["always",{"annotateUndefined":"never"}]
(foo) => { return undefined; }

// Options: ["always",{"annotateUndefined":"never"}]
(foo) => { return void 0; }

// Options: ["always",{"annotateUndefined":"always"}]
(foo): undefined => { return undefined; }

// Options: ["always",{"annotateUndefined":"always"}]
(foo): void => { return void 0; }

// Options: ["always"]
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
(foo) => { return 1; }

// Options: ["always",{"annotateUndefined":"always"}]
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
(foo) => { return undefined; }

// Options: ["always",{"annotateUndefined":"always"}]
async function doThing(): Promise<void> {}

// Options: ["always",{"annotateUndefined":"always"}]
function* doThing(): Generator<number, void, void> { yield 2; }

// Options: ["always",{"annotateUndefined":"always","excludeMatching":["constructor"]}]
class Test { constructor() { } }

class Test { constructor() { } }

// Options: ["always",{"excludeMatching":["foo"]}]
class Test { foo() { return 42; } }

// Options: ["always",{"excludeMatching":["foo"]}]
class Test { foo = () => { return 42; } }

// Options: ["always",{"excludeMatching":["foo"]}]
class Test { foo = () => 42; }

class Test { foo = (): number => { return 42; } }

class Test { foo = (): number => 42; }

async (foo): Promise<number> => { return 3; }

// Options: ["always",{"excludeArrowFunctions":true}]
() => 3

// Options: ["always",{"excludeArrowFunctions":true}]
() => { return 4; }

// Options: ["always",{"excludeArrowFunctions":true}]
() => undefined

// Options: ["always",{"annotateUndefined":"always","excludeArrowFunctions":true}]
() => undefined

// Options: ["always",{"annotateUndefined":"always","excludeArrowFunctions":true}]
() => { return undefined; }

// Options: ["always",{"excludeArrowFunctions":"expressionsOnly"}]
() => 3

// Options: ["always",{"excludeArrowFunctions":"expressionsOnly"}]
async () => 3

// Options: ["always",{"excludeMatching":["foo"]}]
function foo() { return 42; }

// Options: ["always",{"includeOnlyMatching":["bar"]}]
function foo() { return 42; }

// Options: ["always",{"excludeMatching":["bar"]}]
function foo(): number { return 42; }
function bar() { return 42; }

// Options: ["always",{"includeOnlyMatching":["foo","baz"]}]
function foo(): number { return 42; }
function bar() { return 42; }

// Options: ["always",{"excludeMatching":["^b.*","qux"]}]
function foo(): number { return 42; }
function bar() { return 42; }

// Options: ["always",{"includeOnlyMatching":["^f.*"]}]
function foo(): number { return 42; }
function bar() { return 42; }

require-valid-file-annotation

This rule validates Flow file annotations.

This rule can optionally report missing or missed placed annotations, common typos (e.g. // @floww), and enforce a consistant annotation style.

Options

The rule has a string option:

  • "never" (default): Never report files that are missing an @flow annotation.
  • "always": Always report files that are missing an @flow annotation

This rule has an object option:

  • "annotationStyle" - Enforce a consistant file annotation style.
    • "none" (default): Either annotation style is accepted.
    • "line": Require single line annotations (i.e. // @flow).
    • "block": Require block annotations (i.e. /* @flow */).
{
  "rules": {
    "flowtype/require-valid-file-annotation": [
      2,
      "always"
    ]
  }
}

{
  "rules": {
    "flowtype/require-valid-file-annotation": [
      2,
      "always", {
        "annotationStyle": "block"
      }
    ]
  }
}

The following patterns are considered problems:

;// @flow
// Message: Flow file annotation not at the top of the file.

;
// @flow
// Message: Flow file annotation not at the top of the file.

// @Flow
// Message: Malformed Flow file annotation.

// @NoFlow
// Message: Malformed Flow file annotation.

// @Noflow
// Message: Malformed Flow file annotation.

// @floweeeeeee
// Message: Misspelled or malformed Flow file annotation.

// @nofloweeeeeee
// Message: Misspelled or malformed Flow file annotation.

// Options: ["always"]
a;
// Message: Flow file annotation is missing.

// Options: ["always",{"annotationStyle":"line"}]
/* @flow */
// Message: Flow file annotation style must be `// @flow`

// Options: ["always",{"annotationStyle":"block"}]
// @flow
// Message: Flow file annotation style must be `/* @flow */`

// Options: ["always",{"annotationStyle":"line"}]
/* @noflow */
// Message: Flow file annotation style must be `// @noflow`

// Options: ["always",{"annotationStyle":"block"}]
// @noflow
// Message: Flow file annotation style must be `/* @noflow */`

The following patterns are not considered problems:

a;

// @flow
a;

//@flow
a;

//**@flow
a;

/* foo @flow bar */
a;



// @flow
a;

// @flow
// @FLow

// @noflow
a;

// Options: ["always"]
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
a;

// Options: ["always",{"annotationStyle":"line"}]
// @flow

// Options: ["never",{"annotationStyle":"none"}]
// @function

// Options: ["never"]
// @fixable

// Options: ["always",{"annotationStyle":"block"}]
/* @flow */

require-variable-type

Requires that all variable declarators have type annotations.

Options

You can exclude variables that match a certain regex by using excludeVariableMatch.

This excludes all parameters that start with an underscore (_). The default pattern is a^, which doesn't match anything, i.e., all parameters are checked.

{
    "rules": {
        "flowtype/require-variable-type": [
            2,
            {
              "excludeVariableMatch": "^_"
            }
        ]
    }
}

You can choose specific variable types (var, let, and const) to ignore using excludeVariableTypes.

This excludes var and let declarations from needing type annotations, but forces const declarations to have it. By default, all declarations are checked.

{
    "rules": {
        "flowtype/require-variable-type": [
            2,
            {
              "excludeVariableTypes": {
                "var": true,
                "let": true,
                "const": false,
              }
            }
        ]
    }
}

The following patterns are considered problems:

var foo = "bar"
// Message: Missing "foo" variable type annotation.

var foo : string = "bar", bar = 1
// Message: Missing "bar" variable type annotation.

// Options: [{"excludeVariableMatch":"^_"}]
var _foo = "bar", bar = 1
// Message: Missing "bar" variable type annotation.

// Options: [{"excludeVariableTypes":{"let":false,"var":true}}]
var foo = "bar", bar = 1; const oob : string = "oob"; let hey = "yah"
// Message: Missing "hey" variable type annotation.

The following patterns are not considered problems:

var foo : string = "bar"

var foo : string = "bar", bar : number = 1

// Options: [{"excludeVariableMatch":"^_"}]
var _foo = "bar", bar : number = 1

// Options: [{"excludeVariableTypes":{"var":true}}]
var foo = "bar", bar = 1

// Options: [{"excludeVariableTypes":{"let":true,"var":true}}]
var foo = "bar", bar = 1; const oob : string = "oob"; let hey = "yah"

semi

The --fix option on the command line automatically fixes problems reported by this rule.

Enforces consistent use of semicolons after type aliases.

This rule takes one argument. If it is 'never' then a problem is raised when there is a semicolon after a type alias. If it is 'always' then a problem is raised when there is no semicolon after a type alias.

The default value is 'always'.

The following patterns are considered problems:

// Options: []
type FooType = {}
// Message: Missing semicolon.

// Options: ["always"]
type FooType = {}
// Message: Missing semicolon.

// Options: ["never"]
type FooType = {};
// Message: Extra semicolon.

The following patterns are not considered problems:

type FooType = {};

// Options: ["always"]
type FooType = {};

// Options: ["always"]
type FooType = { a: number;
 b: string;
 };

// Options: ["never"]
type FooType = { a: number;
 b: string;
 }

// Options: ["never"]
type FooType = {}

// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
type FooType = {}

sort-keys

The --fix option on the command line automatically fixes problems reported by this rule.

Enforces sorting of Object annotations.

This rule mirrors ESlint's sort-keys rule.

Options

The first option specifies sort order.

  • "asc" (default) - enforce ascending sort order.
  • "desc" - enforce descending sort order.

The second option takes an object with two possible properties.

  • caseSensitive - if true, enforce case-sensitive sort order. Default is true.
  • natural - if true, enforce natural sort order. Default is false.
{
  "rules": {
    "flowtype/sort-keys": [
      2,
      "asc", {
        "caseSensitive": true,
        "natural": false
      }
    ]
  }
}

The following patterns are considered problems:

type FooType = { a: number, c: number, b: string }
// Message: Expected type annotations to be in ascending order. "b" should be before "c".

type FooType = { a: number, b: number, C: number }
// Message: Expected type annotations to be in ascending order. "C" should be before "b".

type FooType = { 1: number, 2: number, 10: number }
// Message: Expected type annotations to be in ascending order. "10" should be before "2".

// Options: ["desc"]
type FooType = { a: number, b: number }
// Message: Expected type annotations to be in descending order. "b" should be before "a".

// Options: ["desc"]
type FooType = { C: number, b: number, a: string }
// Message: Expected type annotations to be in descending order. "b" should be before "C".

// Options: ["desc"]
type FooType = { 10: number, 2: number, 1: number }
// Message: Expected type annotations to be in descending order. "2" should be before "10".

// Options: ["asc",{"caseSensitive":false}]
type FooType = { a: number, c: number, C: number, b: string }
// Message: Expected type annotations to be in insensitive ascending order. "b" should be before "C".

// Options: ["asc",{"caseSensitive":false}]
type FooType = { a: number, C: number, c: number, b: string }
// Message: Expected type annotations to be in insensitive ascending order. "b" should be before "c".

// Options: ["asc",{"natural":true}]
type FooType = { 1: number, 10: number, 2: boolean }
// Message: Expected type annotations to be in natural ascending order. "2" should be before "10".

type FooType = { a: number, c: number, b: string }
// Message: Expected type annotations to be in ascending order. "b" should be before "c".


        type FooType = {
          a: number,
          c: number,
          b: string,
        }

// Message: Expected type annotations to be in ascending order. "b" should be before "c".


        type FooType = {
          +a: number,
          c: number,
          b: string,
        }

// Message: Expected type annotations to be in ascending order. "b" should be before "c".


        type FooType = {
          -a: number,
          c: number,
          b: string,
        }

// Message: Expected type annotations to be in ascending order. "b" should be before "c".


        type FooType = {
          a?: number,
          c: ?number,
          b: string,
        }

// Message: Expected type annotations to be in ascending order. "b" should be before "c".


        type FooType = {
          a: (number) => void,
          c: number,
          b: (param: string) => number,
        }

// Message: Expected type annotations to be in ascending order. "b" should be before "c".


        type FooType = {
          a: number | string | boolean,
          c: number,
          b: (param: string) => number,
        }

// Message: Expected type annotations to be in ascending order. "b" should be before "c".


        type FooType = {
          c: number,
          a: number | string | boolean,
          b: (param: string) => number,
        }

// Message: Expected type annotations to be in ascending order. "a" should be before "c".


        type FooType = {
          c: {
            z: number,
            x: string,
            y: boolean,
          },
          a: number | string | boolean,
          b: (param: string) => number,
        }

// Message: Expected type annotations to be in ascending order. "x" should be before "z".
// Message: Expected type annotations to be in ascending order. "a" should be before "c".


        type FooType = {
          c: {
            z: {
              j: string,
              l: number,
              k: boolean,
            },
            x: string,
            y: boolean,
          },
          a: number | string | boolean,
          b: (param: string) => number,
        }

// Message: Expected type annotations to be in ascending order. "k" should be before "l".
// Message: Expected type annotations to be in ascending order. "x" should be before "z".
// Message: Expected type annotations to be in ascending order. "a" should be before "c".

The following patterns are not considered problems:

type FooType = { a: number }

type FooType = { a: number, b: number, c: (boolean | number) }

type FooType = { C: number, a: string, b: foo }

type FooType = { 1: number, 10: number, 2: boolean }

// Options: ["desc"]
type FooType = { c: number, b: number, a: number }

// Options: ["desc"]
type FooType = { b: string, a: {}, C: number }

// Options: ["desc"]
type FooType = { 2: number, 10: number, 1: boolean }

// Options: ["asc",{"caseSensitive":false}]
type FooType = { a: number, b: number, c: number, C: number }

// Options: ["asc",{"caseSensitive":false}]
type FooType = { a: number, b: number, C: number, c: number }

// Options: ["asc",{"natural":true}]
type FooType = { 1:number, 2: number, 10: number }

// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
type FooType = { b: number, a: number }

space-after-type-colon

The --fix option on the command line automatically fixes problems reported by this rule.

Enforces consistent spacing after the type annotation colon.

Options

This rule has a string argument.

  • "always" (default): Require a space after the type annotation colon (e.g. foo: BarType).
  • "never": Require no spaces after the type annotation colon (e.g. foo:BarType).

This rule has an option object.

  • "allowLineBreak" - Allow a line break to count as a space following the annotation colon.
    • "true": Enable
    • "false": Disable

{ rules: { flowtype/space-after-type-colon: [ 2, always, { allowLineBreak: false } ] } }

The following patterns are considered problems:

// Options: ["never"]
(foo: string) => {}
// Message: There must be no space after "foo" parameter type annotation colon.

// Options: ["always"]
(foo:  string) => {}
// Message: There must be 1 space after "foo" parameter type annotation colon.

// Options: ["always"]
(foo:(() => void)) => {}
// Message: There must be a space after "foo" parameter type annotation colon.

// Options: ["never"]
(foo: (() => void)) => {}
// Message: There must 
eslint-plugin-flowtype open issues Ask a question     (View All Issues)
  • over 2 years Add rule to enforce defined types or built-in types
  • over 2 years Whitelist / blacklist function names for require-return-type et al.
  • over 2 years Space after curly braces?
  • over 2 years Support Flow 34 optional names
  • over 2 years New rule: Warn on mix of "declare" with implementation code
  • over 2 years The no-dupe-keys rule complains about legal duplicated keys in a declared class
  • over 2 years Not all rules respect onlyFilesWithFlowAnnotation
  • over 2 years Use Flow type information, e.g. for require-parameter-type
  • over 2 years Odd errors from no-undef rule
  • almost 3 years define-flow-type is overly loose
  • almost 3 years flowtype/require-valid-file-annotation
  • almost 3 years Add rule to enforce one array notation style
  • almost 3 years Rule for requiring types for fn definitions only
  • almost 3 years Add rule for requiring class property names to be declared
  • almost 3 years Support /* Flow Comments */
  • almost 3 years Using "declare interface" or "declare type" syntax incorrectly triggers "no-undef" rule while "declare class" does not have this issue.
  • almost 3 years Add `type-param-id-match` rule
  • almost 3 years import is duplicated when using `import` and `import type`
  • almost 3 years distinguish between "flow" and "flow weak" files
  • almost 3 years Add `require-parameter-type` option to ignore object maps
  • almost 3 years Add `require-parameter-type` option to ignore function expressions
  • almost 3 years Combine define & use-flowType rules
  • almost 3 years Extend `valid-jsdoc` core rule by adding `requireParamTypes` option
  • almost 3 years space-after-type-colon should accept newlines
  • about 3 years Add rule for requiring variable type
eslint-plugin-flowtype open pull requests (View All Pulls)
  • Allow require-parameter-type to take ignoreParameterNames option
  • feat: ObjectTypeIndexer in spaceBeforeTypeColon & spaceAfterTypeColon
  • feat: allow line break to satisfy trailing space rule (fixes #31)
  • fix: annotation spell check, better @noflow support (fixes #106)
  • Add rule for requiring variable type
  • fix: no-dupe-keys with legal duplicated keys (fixes #133)
  • feat: add flowtype-errors
  • feat: `require-return-type` include / exclude filter support (fixes #149)
  • Implement 'fix' for the require-valid-file-annotation rule
  • Update `looksLikeFlowFileAnnotation` regex to match only @flow
  • feat: add rules for nullable and optional spacing (WIP)
  • feat: support arrow function type shorthand
  • feat: add variable declarations to colon spacing checks (fixes #178)
  • Add utility types as globals
  • Prevent crash when using types with spreads
  • feat: Array style rules
  • fix: Don't crash on type spread in no-dupe-keys
  • feat: add rule that only requires types for exported functions and variables
  • Add missing keys
  • #266 #302 #293 Prevent crash when using types with spreads
  • fix: object-type-delimeter with new babel-eslint
  • Automatically include plugin when extending preset, fixes #313
eslint-plugin-flowtype list of languages used
eslint-plugin-flowtype latest release notes
v2.46.1 v2.46.1

2.46.1 (2018-02-22)

Bug Fixes

  • (type-import-style) Support import aliases when fixing (#321) (d7ccd0dd)
v2.46.0 v2.46.0

2.46.0 (2018-02-21)

Features

  • add type-import-style rule (#320) (3c672237)
v2.45.0 v2.45.0

2.45.0 (2018-02-18)

Features

  • add require-types-at-top rule (, #168, #285) (74bcb8c1, closes #319)
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