# eslint-plugin-flowtype

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[Flow type](http://flowtype.org/) linting rules for ESLint.

* [eslint-plugin-flowtype](#eslint-plugin-flowtype)
    * [Installation](#eslint-plugin-flowtype-installation)
    * [Configuration](#eslint-plugin-flowtype-configuration)
        * [Shareable configurations](#eslint-plugin-flowtype-configuration-shareable-configurations)
    * [Settings](#eslint-plugin-flowtype-settings)
        * [`onlyFilesWithFlowAnnotation`](#eslint-plugin-flowtype-settings-onlyfileswithflowannotation)
    * [Rules](#eslint-plugin-flowtype-rules)
        * [`boolean-style`](#eslint-plugin-flowtype-rules-boolean-style)
        * [`define-flow-type`](#eslint-plugin-flowtype-rules-define-flow-type)
        * [`delimiter-dangle`](#eslint-plugin-flowtype-rules-delimiter-dangle)
        * [`generic-spacing`](#eslint-plugin-flowtype-rules-generic-spacing)
        * [`no-dupe-keys`](#eslint-plugin-flowtype-rules-no-dupe-keys)
        * [`no-weak-types`](#eslint-plugin-flowtype-rules-no-weak-types)
        * [`object-type-delimiter`](#eslint-plugin-flowtype-rules-object-type-delimiter)
        * [`require-parameter-type`](#eslint-plugin-flowtype-rules-require-parameter-type)
        * [`require-return-type`](#eslint-plugin-flowtype-rules-require-return-type)
        * [`require-valid-file-annotation`](#eslint-plugin-flowtype-rules-require-valid-file-annotation)
        * [`semi`](#eslint-plugin-flowtype-rules-semi)
        * [`sort-keys`](#eslint-plugin-flowtype-rules-sort-keys)
        * [`space-after-type-colon`](#eslint-plugin-flowtype-rules-space-after-type-colon)
        * [`space-before-generic-bracket`](#eslint-plugin-flowtype-rules-space-before-generic-bracket)
        * [`space-before-type-colon`](#eslint-plugin-flowtype-rules-space-before-type-colon)
        * [`type-id-match`](#eslint-plugin-flowtype-rules-type-id-match)
        * [`union-intersection-spacing`](#eslint-plugin-flowtype-rules-union-intersection-spacing)
        * [`use-flow-type`](#eslint-plugin-flowtype-rules-use-flow-type)
        * [`valid-syntax`](#eslint-plugin-flowtype-rules-valid-syntax)

## Installation

1. Install [ESLint](https://www.github.com/eslint/eslint).
1. Install [`babel-eslint`](https://github.com/babel/babel-eslint) parser (ESLint parser [does not support type annotations](https://github.com/eslint/eslint/issues/2157)).
1. Install [`eslint-plugin-flowtype`](https://github.com/gajus/eslint-plugin-flowtype) plugin.



```sh
npm install eslint
npm install babel-eslint
npm install eslint-plugin-flowtype
```


## Configuration

1. Set `parser` property to `babel-eslint`.
1. Add `plugins` section and specify `eslint-plugin-flowtype` as a plugin.
1. Enable rules.



```json
{
  "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-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](./src/configs/recommended.json) that enforces Flow type good practices.

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

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

See [ESLint documentation](http://eslint.org/docs/user-guide/configuring#extending-configuration-files) for more information about extending configuration files.

## Settings

### onlyFilesWithFlowAnnotation

When `true`, only checks files with a [`@flow` annotation](http://flowtype.org/docs/about-flow.html#gradual) in the first comment.

```js
{
  "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:

```js
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:

```js
type X = boolean

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

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


### define-flow-type

Marks Flow type identifiers as defined.

Used to suppress [`no-undef`](http://eslint.org/docs/rules/no-undef) reporting of type identifiers.

The following patterns are not considered problems:

```js
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}

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}

({ 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"]}

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"]}

({ 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:

```js
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:

```js
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:

```js
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:

```js
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](http://eslint.org/docs/rules/no-dupe-keys) rule.

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

The following patterns are considered problems:

```js
type FooType = { a: number, b: string, a: number }
// Message: Duplicate property.

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

The following patterns are not considered problems:

```js
type FooType = { a: number, b: string, c: 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`:

```js
{
    "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:

```js
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:

```js
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
```


### 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:

```js
// 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:

```js
// 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, }
```


### 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.

```js
{
    "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`.

```js
{
    "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:

```js
(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.

// @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:

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

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

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

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

([foo]: Array) => {}

(foo) => {}

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

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

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

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


### 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 want to exclude only concise arrow function (e.g. `() => 2`). Provide `excludeArrowFunctions` with `expressionsOnly` for this.

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

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

The following patterns are considered problems:

```js
(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.

// @flow
(foo) => { return 1; }
// Message: Missing return type annotation.

// Options: ["always",{"annotateUndefined":"always"}]
// @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"]
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.
```

The following patterns are not considered problems:

```js
(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"]
(foo) => { return 1; }

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

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

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

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
```


### 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 */`).

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

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

The following patterns are considered problems:

```js
;// @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.

// @floweeeeeee
// Message: Malformed flow file annotation.

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

// @nofloweeeeeee
// Message: 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 */`
```

The following patterns are not considered problems:

```js
a;

// @flow
a;

//@flow
a;

//**@flow
a;

/* foo @flow bar */
a;



// @flow
a;

// @flow
// @FLow

// @noflow
a;

// Options: ["always"]
a;

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

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


### 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:

```js
// 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:

```js
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 = {}
```


### sort-keys

Enforces sorting of Object annotations.

This rule mirrors ESlint's [sort-keys](http://eslint.org/docs/rules/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](https://en.wikipedia.org/wiki/Natural_sort_order). Default is `false`.

```js
{
  "rules": {
    "flowtype/sort-keys": [
      2,
      "asc", {
        "caseSensitive": true,
        "natural": false
      }
    ]
  }
}
```

The following patterns are considered problems:

```js
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".
```

The following patterns are not considered problems:

```js
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 }
```


### 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.

This rule takes one argument. If it is `'always'` then a problem is raised when there is no space after the type annotation colon. If it is `'never'` then a problem is raised when there is a space after the type annotation colon. The default value is `'always'`.

The following patterns are considered problems:

```js
// 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 be no space after "foo" parameter type annotation colon.

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

({ lorem, ipsum, dolor } :   SomeType) => {}
// Message: There must be 1 space after "{ lorem, ipsum, dolor }" parameter type annotation colon.

(foo:{ a: string, b: number }) => {}
// Message: There must be a space after "foo" parameter type annotation colon.

({ a, b } :{ a: string, b: number }) => {}
// Message: There must be a space after "{ a, b }" parameter type annotation colon.

([ a, b ] :string[]) => {}
// Message: There must be a space after "[ a, b ]" parameter type annotation colon.

(i?:number) => {}
// Message: There must be a space after "i" parameter type annotation colon.

(i?:  number) => {}
// Message: There must be 1 space after "i" parameter type annotation colon.

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

// Options: ["always"]
():Object => {}
// Message: There must be a space after return type colon.

// Options: ["never"]
(): Object => {}
// Message: There must be no space after return type colon.

// Options: ["always"]
():  Object => {}
// Message: There must be 1 space after return type colon.

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

// Options: ["never"]
(): (() => void) => {}
// Message: There must be no space after return type colon.

// Options: ["always"]
():  (() => void) => {}
// Message: There must be 1 space after return type colon.

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

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

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

function foo (foo:string) {}
// Message: There must be a space after "foo" parameter type annotation colon.

async function foo({ lorem, ipsum, dolor }:SomeType) {}
// Message: There must be a space after "{ lorem, ipsum, dolor }" parameter type annotation colon.

function x(i?:number) {}
// Message: There must be a space after "i" parameter type annotation colon.

function x(i?:  number) {}
// Message: There must be 1 space after "i" parameter type annotation colon.

// Options: ["never"]
function x(i?: number) {}
// Message: There must be no space after "i" parameter type annotation colon.

function a():x {}
// Message: There must be a space after return type colon.

// Options: ["always"]
function a():  x {}
// Message: There must be 1 space after return type colon.

// Options: ["never"]
function a(): x {}
// Message: There must be no space after return type colon.

type X = (foo:number) => string
// Message: There must be a space after "foo" parameter type annotation colon.

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

type X = (foo:  number) => string
// Message: There must be 1 space after "foo" parameter type annotation colon.

type X = (foo:?number) => string
// Message: There must be a space after "foo" parameter type annotation colon.

type X = (foo:(number)) => string
// Message: There must be a space after "foo" parameter type annotation colon.

type X = (foo:((number))) => string
// Message: There must be a space after "foo" parameter type annotation colon.

type X = (foo:  ((number))) => string
// Message: There must be 1 space after "foo" parameter type annotation colon.

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

type X = (foo:?(number)) => string
// Message: There must be a space after "foo" parameter type annotation colon.

type TArrayPredicate = (el: T, i?:number) => boolean
// Message: There must be a space after "i" parameter type annotation colon.

type TArrayPredicate = (el: T, i?:  number) => boolean
// Message: There must be 1 space after "i" parameter type annotation colon.

// Options: ["never"]
type TArrayPredicate = (el:T, i?: number) => boolean
// Message: There must be no space after "i" parameter type annotation colon.

class X { foo:string }
// Message: There must be a space after "foo" class property type annotation colon.

// Options: ["never"]
class X { foo: string }
// Message: There must be no space after "foo" class property type annotation colon.

class X { foo:?string }
// Message: There must be a space after "foo" class property type annotation colon.

// Options: ["never"]
class X { foo: ?string }
// Message: There must be no space after "foo" class property type annotation colon.

class X { static foo:number }
// Message: There must be a space after "foo" class property type annotation colon.

// Options: ["never"]
class X { static foo: number }
// Message: There must be no space after "foo" class property type annotation colon.

class X { static foo :number }
// Message: There must be a space after "foo" class property type annotation colon.

// Options: ["never"]
class X { static foo : number }
// Message: There must be no space after "foo" class property type annotation colon.

declare class X { static foo:number }
// Message: There must be a space after "foo" type annotation colon.

// Options: ["never"]
declare class X { static foo: number }
// Message: There must be no space after "foo" type annotation colon.

declare class X { static foo :number }
// Message: There must be a space after "foo" type annotation colon.

// Options: ["never"]
declare class X { static foo : number }
// Message: There must be no space after "foo" type annotation colon.

class X { +foo:string }
// Message: There must be a space after "foo" class property type annotation colon.

class X { +foo:  string }
// Message: There must be 1 space after "foo" class property type annotation colon.

// Options: ["never"]
class X { +foo: string }
// Message: There must be no space after "foo" class property type annotation colon.

class X { static +foo:string }
// Message: There must be a space after "foo" class property type annotation colon.

class X { static +foo:  string }
// Message: There must be 1 space after "foo" class property type annotation colon.

// Options: ["never"]
class X { static +foo: string }
// Message: There must be no space after "foo" class property type annotation colon.

type X = { foo:string }
// Message: There must be a space after "foo" type annotation colon.

// Options: ["always"]
type X = { foo:string }
// Message: There must be a space after "foo" type annotation colon.

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

type X = { foo:  string }
// Message: There must be 1 space after "foo" type annotation colon.

type X = { foo?:string }
// Message: There must be a space after "foo" type annotation colon.

// Options: ["never"]
type X = { foo?: string }
// Message: There must be no space after "foo" type annotation colon.

type X = { foo?:?string }
// Message: There must be a space after "foo" type annotation colon.

type X = { foo?:  ?string }
// Message: There must be 1 space after "foo" type annotation colon.

type Foo = { barType:(string | () => void) }
// Message: There must be a space after "barType" type annotation colon.

type Foo = { barType:(((string | () => void))) }
// Message: There must be a space after "barType" type annotation colon.

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

type Foo = { barType:  (string | () => void) }
// Message: There must be 1 space after "barType" type annotation colon.

type Foo = { barType:  ((string | () => void)) }
// Message: There must be 1 space after "barType" type annotation colon.

type X = { get:() => A; }
// Message: There must be a space after "get" type annotation colon.

type X = { get:<X>() => A; }
// Message: There must be a space after "get" type annotation colon.

// Options: ["never"]
type X = { get: () => A; }
// Message: There must be no space after "get" type annotation colon.

// Options: ["never"]
type X = { get: <X>() => A; }
// Message: There must be no space after "get" type annotation colon.

type X = { get:  () => A; }
// Message: There must be 1 space after "get" type annotation colon.

type X = { get:  <X>() => A; }
// Message: There must be 1 space after "get" type annotation colon.

type X = { +foo:string }
// Message: There must be a space after "foo" type annotation colon.

type X = { +foo:  string }
// Message: There must be 1 space after "foo" type annotation colon.

// Options: ["never"]
type X = { +foo: string }
// Message: There must be no space after "foo" type annotation colon.

type X = { +foo?:string }
// Message: There must be a space after "foo" type annotation colon.

type X = { +foo?:  string }
// Message: There must be 1 space after "foo" type annotation colon.

// Options: ["never"]
type X = { +foo?: string }
// Message: There must be no space after "foo" type annotation colon.

// Options: ["always"]
type X = { [a:b]: c }
// Message: There must be a space after type annotation colon.

// Options: ["never"]
type X = { [a: b]:c }
// Message: There must be no space after type annotation colon.

// Options: ["always"]
type X = { [a:    b]: c }
// Message: There must be 1 space after type annotation colon.

// Options: ["always"]
type X = { +[a:b]: c }
// Message: There must be a space after type annotation colon.

// Options: ["never"]
type X = { +[a: b]:c }
// Message: There must be no space after type annotation colon.

// Options: ["always"]
type X = { +[a:    b]: c }
// Message: There must be 1 space after type annotation colon.

// Options: ["always"]
type X = { [a: b]:c }
// Message: There must be a space after type annotation colon.

// Options: ["never"]
type X = { [a:b]: c }
// Message: There must be no space after type annotation colon.

// Options: ["always"]
type X = { [a: b]:    c }
// Message: There must be 1 space after type annotation colon.

// Options: ["always"]
type X = { [a:b]:c }
// Message: There must be a space after type annotation colon.
// Message: There must be a space after type annotation colon.

// Options: ["never"]
type X = { [a: b]: c }
// Message: There must be no space after type annotation colon.
// Message: There must be no space after type annotation colon.

// Options: ["always"]
type X = { [a:  b]:  c }
// Message: There must be 1 space after type annotation colon.
// Message: There must be 1 space after type annotation colon.

// Options: ["always"]
type X = { [a:(b)]:(c) }
// Message: There must be a space after type annotation colon.
// Message: There must be a space after type annotation colon.

// Options: ["never"]
type X = { [a: (b)]: (c) }
// Message: There must be no space after type annotation colon.
// Message: There must be no space after type annotation colon.

// Options: ["never"]
const x = ({}: {})
// Message: There must be no space after type cast colon.

// Options: ["always"]
const x = ({}:{})
// Message: There must be a space after type cast colon.

// Options: ["always"]
const x = ({}:  {})
// Message: There must be 1 space after type cast colon.

// Options: ["never"]
((x): (string))
// Message: There must be no space after type cast colon.

// Options: ["always"]
((x):(string))
// Message: There must be a space after type cast colon.

// Options: ["always"]
((x):  (string))
// Message: There must be 1 space after type cast colon.
```

The following patterns are not considered problems:

```js
(foo) => {}

(foo: string) => {}

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

// Options: ["never"]
(foo:string) => {}

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

// Options: ["never"]
(foo:(() => void)) => {}

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

({ lorem, ipsum, dolor }: SomeType) => {}

(foo: { a: string, b: number }) => {}

({ a, b }: ?{ a: string, b: number }) => {}

([ a, b ]: string[]) => {}

(i?: number) => {}

// Options: ["never"]
(i?:number) => {}

// Options: ["never"]
():Object => {}

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

// Options: ["never"]
():(number | string) => {}

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

// Options: ["never"]
():number|string => {}

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

// Options: ["never"]
():(() => void) => {}

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

// Options: ["never"]
():( () => void ) => {}

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

(): { a: number, b: string } => {}

// Options: ["never"]
() :{ a:number, b:string } => {}

function x(foo: string) {}

class Foo { constructor(foo: string) {} }

// Options: ["never"]
function x(foo:string) {}

// Options: ["never"]
class Foo { constructor(foo:string) {} }

async function foo({ lorem, ipsum, dolor }: SomeType) {}

function x({ a, b }: { a: string, b: number }) {}

function x(i?: number) {}

// Options: ["never"]
function x(i?:number) {}

function a(): x {}

// Options: ["never"]
function a():x {}

function a(): (number | string) {}

// Options: ["never"]
function a() :(number | string) {}

type X = (foo: number) => string;

type X = (foo : number) => string;

type X = (foo: ?number) => string;

type X = (foo? : ?number) => string;

type X = (foo: ?{ x: number }) => string;

// Options: ["never"]
type X = (foo:number) => string;

// Options: ["never"]
type X = (foo:?{ x:number }) => string;

type X = (foo: (number)) => string

type X = (foo: ((number))) => string

// Options: ["never"]
type X = (foo:((number))) => string

type X = ?(foo: ((number))) => string

// Options: ["never"]
type X = ?(foo:((number))) => string

type TArrayPredicate = (el: T, i?: number) => boolean

// Options: ["never"]
type TArrayPredicate = (el:T, i?:number) => boolean

class Foo { bar }

class Foo { bar = 3 }

class Foo { bar: string }

class Foo { bar: ?string }

// Options: ["never"]
class Foo { bar:string }

// Options: ["never"]
class Foo { bar:?string }

class X { static foo : number }

// Options: ["never"]
class X { static foo :number }

declare class X { static foo : number }

// Options: ["never"]
declare class X { static foo :number }

class X { +foo: string }

class X { static +foo: string }

// Options: ["never"]
class X { +foo:string }

// Options: ["never"]
class X { static +foo:string }

type X = { foo: string }

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

type X = { foo?: string }

type X = { foo?: ?string }

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

type Foo = { barType: (string | () => void) }

type Foo = { barType: ((string | () => void)) }

// Options: ["never"]
type Foo = { barType:(string | () => void) }

// Options: ["never"]
type Foo = { barType:((string | () => void)) }

type X = { get(): A; }

type X = { get<X>(): A; }

// Options: ["never"]
type X = { get(): A; }

// Options: ["never"]
type X = { get<X>(): A; }

type X = { get: () => A; }

type X = { get: <X>() => A; }

// Options: ["never"]
type X = { get:() => A; }

// Options: ["never"]
type X = { get:<X>() => A; }

type X = { +foo: string }

type X = { +foo?: string }

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

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

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

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

// Options: ["always"]
type X = { +[a: b]: c }

// Options: ["never"]
type X = { +[a:b]:c }

// Options: ["never"]
const x = ({}:{})

// Options: ["always"]
const x = ({}: {})

// Options: ["never"]
((x):(string))

// Options: ["always"]
((x): (string))
```


### space-before-generic-bracket

_The `--fix` option on the command line automatically fixes problems reported by this rule._

Enforces consistent spacing before the opening `<` of generic type annotation parameters.

This rule takes one argument. If it is `'never'` then a problem is raised when there is a space before the `<`. If it is `'always'` then a problem is raised when there is no space before the `<`.

The default value is `'never'`.

The following patterns are considered problems:

```js
type X = Promise <string>
// Message: There must be no space before "Promise" generic type annotation bracket

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

type X = Promise  <string>
// Message: There must be no space before "Promise" generic type annotation bracket

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

// Options: ["always"]
type X = Promise  <string>
// Message: There must be one space before "Promise" generic type annotation bracket
```

The following patterns are not considered problems:

```js
type X = Promise<string>

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


### space-before-type-colon

_The `--fix` option on the command line automatically fixes problems reported by this rule._

Enforces consistent spacing before the type annotation colon.

This rule takes one argument. If it is `'always'` then a problem is raised when there is no space before the type annotation colon. If it is `'never'` then a problem is raised when there is a space before the type annotation colon. The default value is `'never'`.

The following patterns are considered problems:

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

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

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

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

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

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

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

({ lorem, ipsum, dolor } : SomeType) => {}
// Message: There must be no space before "{ lorem, ipsum, dolor }" parameter type annotation colon.

(foo : { a: string, b: number }) => {}
// Message: There must be no space before "foo" parameter type annotation colon.

({ a, b } : { a: string, b: number }) => {}
// Message: There must be no space before "{ a, b }" parameter type annotation colon.

([ a, b ] : string[]) => {}
// Message: There must be no space before "[ a, b ]" parameter type annotation colon.

() : x => {}
// Message: There must be no space before return type colon.

// Options: ["always"]
(): x => {}
// Message: There must be a space before return type colon.

// Options: ["always"]
()  : x => {}
// Message: There must be 1 space before return type colon.

function x(foo : string) {}
// Message: There must be no space before "foo" parameter type annotation colon.

// Options: ["always"]
function x(foo: string) {}
// Message: There must be a space before "foo" parameter type annotation colon.

var x = function (foo : string) {}
// Message: There must be no space before "foo" parameter type annotation colon.

// Options: ["always"]
var x = function (foo: string) {}
// Message: There must be a space before "foo" parameter type annotation colon.

class Foo { constructor(foo : string ) {} }
// Message: There must be no space before "foo" parameter type annotation colon.

// Options: ["always"]
class Foo { constructor(foo: string ) {} }
// Message: There must be a space before "foo" parameter type annotation colon.

async function foo({ lorem, ipsum, dolor } : SomeType) {}
// Message: There must be no space before "{ lorem, ipsum, dolor }" parameter type annotation colon.

function a() : x {}
// Message: There must be no space before return type colon.

// Options: ["always"]
function a(): x {}
// Message: There must be a space before return type colon.

// Options: ["always"]
function a()  : x {}
// Message: There must be 1 space before return type colon.

type X = (foo :string) => string;
// Message: There must be no space before "foo" parameter type annotation colon.

// Options: ["always"]
type X = (foo:string) => string;
// Message: There must be a space before "foo" parameter type annotation colon.

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

type X = (foo? :string) => string;
// Message: There must be no space before "foo" parameter type annotation colon.

type X = (foo?     :string) => string;
// Message: There must be no space before "foo" parameter type annotation colon.

// Options: ["always"]
type X = (foo?:string) => string;
// Message: There must be a space before "foo" parameter type annotation colon.

type X = (foo? :?string) => string;
// Message: There must be no space before "foo" parameter type annotation colon.

class X { foo :string }
// Message: There must be no space before "foo" class property type annotation colon.

// Options: ["always"]
class X { foo: string }
// Message: There must be a space before "foo" class property type annotation colon.

class X { foo :?string }
// Message: There must be no space before "foo" class property type annotation colon.

// Options: ["always"]
class X { foo: ?string }
// Message: There must be a space before "foo" class property type annotation colon.

class X { static foo : number }
// Message: There must be no space before "foo" class property type annotation colon.

class X { static foo :number }
// Message: There must be no space before "foo" class property type annotation colon.

// Options: ["always"]
class X { static foo: number }
// Message: There must be a space before "foo" class property type annotation colon.

// Options: ["always"]
class X { static foo:number }
// Message: There must be a space before "foo" class property type annotation colon.

declare class Foo { static bar :number; }
// Message: There must be no space before "bar" type annotation colon.

declare class Foo { static bar : number; }
// Message: There must be no space before "bar" type annotation colon.

// Options: ["always"]
declare class Foo { static bar:number; }
// Message: There must be a space before "bar" type annotation colon.

// Options: ["always"]
declare class Foo { static bar: number; }
// Message: There must be a space before "bar" type annotation colon.

// Options: ["always"]
class X { +foo: string }
// Message: There must be a space before "foo" class property type annotation colon.

// Options: ["always"]
class X { +foo  : string }
// Message: There must be 1 space before "foo" class property type annotation colon.

// Options: ["never"]
class X { +foo : string }
// Message: There must be no space before "foo" class property type annotation colon.

// Options: ["always"]
class X { static +foo: string }
// Message: There must be a space before "foo" class property type annotation colon.

// Options: ["always"]
class X { static +foo  : string }
// Message: There must be 1 space before "foo" class property type annotation colon.

// Options: ["never"]
class X { static +foo : string }
// Message: There must be no space before "foo" class property type annotation colon.

type X = { foo : string }
// Message: There must be no space before "foo" type annotation colon.

// Options: ["never"]
type X = { foo : string }
// Message: There must be no space before "foo" type annotation colon.

// Options: ["always"]
type X = { foo: string }
// Message: There must be a space before "foo" type annotation colon.

// Options: ["always"]
type X = { foo  : string }
// Message: There must be 1 space before "foo" type annotation colon.

type X = { foo? : string }
// Message: There must be no space before "foo" type annotation colon.

// Options: ["always"]
type X = { foo?: string }
// Message: There must be a space before "foo" type annotation colon.

// Options: ["always"]
type X = { foo?  : string }
// Message: There must be 1 space before "foo" type annotation colon.

// Options: ["always"]
type X = { foo   ?: string }
// Message: There must be a space before "foo" type annotation colon.

// Options: ["always"]
type X = { +foo: string }
// Message: There must be a space before "foo" type annotation colon.

// Options: ["always"]
type X = { +foo  : string }
// Message: There must be 1 space before "foo" type annotation colon.

// Options: ["never"]
type X = { +foo : string }
// Message: There must be no space before "foo" type annotation colon.

// Options: ["always"]
type X = { +foo?: string }
// Message: There must be a space before "foo" type annotation colon.

// Options: ["always"]
type X = { +foo?  : string }
// Message: There must be 1 space before "foo" type annotation colon.

// Options: ["never"]
type X = { +foo? : string }
// Message: There must be no space before "foo" type annotation colon.

// Options: ["always"]
type X = { [a: b] : c }
// Message: There must be a space before type annotation colon.

// Options: ["never"]
type X = { [a : b]: c }
// Message: There must be no space before type annotation colon.

// Options: ["always"]
type X = { [a  : b] : c }
// Message: There must be 1 space before type annotation colon.

// Options: ["always"]
type X = { +[a:b] : c }
// Message: There must be a space before type annotation colon.

// Options: ["never"]
type X = { +[a : b]: c }
// Message: There must be no space before type annotation colon.

// Options: ["always"]
type X = { +[a  : b] : c }
// Message: There must be 1 space before type annotation colon.

// Options: ["always"]
type X = { [a : b]: c }
// Message: There must be a space before type annotation colon.

// Options: ["never"]
type X = { [a: b] : c }
// Message: There must be no space before type annotation colon.

// Options: ["always"]
type X = { [a : b]  : c }
// Message: There must be 1 space before type annotation colon.

// Options: ["always"]
type X = { [a:b]:c }
// Message: There must be a space before type annotation colon.
// Message: There must be a space before type annotation colon.

// Options: ["never"]
type X = { [a : b] : c }
// Message: There must be no space before type annotation colon.
// Message: There must be no space before type annotation colon.

// Options: ["always"]
type X = { [a  : b]  : c }
// Message: There must be 1 space before type annotation colon.
// Message: There must be 1 space before type annotation colon.

// Options: ["always"]
type X = { [a:(b)]:(c) }
// Message: There must be a space before type annotation colon.
// Message: There must be a space before type annotation colon.

// Options: ["never"]
type X = { [a : (b)] : (c) }
// Message: There must be no space before type annotation colon.
// Message: There must be no space before type annotation colon.

// Options: ["never"]
const x = ({} :{})
// Message: There must be no space before type cast colon.

// Options: ["always"]
const x = ({}:{})
// Message: There must be a space before type cast colon.

// Options: ["always"]
const x = ({}  :{})
// Message: There must be 1 space before type cast colon.

// Options: ["never"]
((x) : string)
// Message: There must be no space before type cast colon.

// Options: ["always"]
((x): string)
// Message: There must be a space before type cast colon.

// Options: ["always"]
((x)  : string)
// Message: There must be 1 space before type cast colon.
```

The following patterns are not considered problems:

```js
(foo) => {}

(foo: string) => {}

(foo?: string) => {}

(foo ?: string) => {}

// Options: ["never"]
(foo: string) => {}

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

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

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

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

({ lorem, ipsum, dolor }: SomeType) => {}

(foo: { a: string, b: number }) => {}

({ a, b }: ?{ a: string, b: number }) => {}

(): { a: number, b: string } => {}

// Options: ["always"]
() : { a : number, b : string } => {}

([ a, b ]: string[]) => {}

(): x => {}

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

(): (number | string) => {}

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

function x(foo: string) {}

// Options: ["always"]
function x(foo : string) {}

var x = function (foo: string) {}

// Options: ["always"]
var x = function (foo : string) {}

class X { foo({ bar }: Props = this.props) {} }

class Foo { constructor(foo: string ) {} }

// Options: ["always"]
class Foo { constructor(foo : string ) {} }

async function foo({ lorem, ipsum, dolor }: SomeType) {}

function x({ a, b }: { a: string, b: number }) {}

function a(): x {}

// Options: ["always"]
function a() : x {}

function a(): (number | string) {}

// Options: ["always"]
function a() : (number | string) {}

type X = (foo:string) => number;

type X = (foo: string) => number;

type X = (foo: ?string) => number;

type X = (foo?: string) => number;

type X = (foo?: ?string) => number;

type X = (foo   ?: string) => number;

// Options: ["always"]
type X = (foo? : string) => number

// Options: ["always"]
type X = (foo? : ?string) => number

class Foo { bar }

class Foo { bar = 3 }

class Foo { bar: string }

class Foo { bar: ?string }

class Foo { bar:?string }

// Options: ["always"]
class Foo { bar : string }

class X { static foo:number }

class X { static foo: number }

// Options: ["always"]
class X { static foo :number }

// Options: ["always"]
class X { static foo : number }

declare class Foo { static bar:number; }

// Options: ["always"]
declare class Foo { static bar :number; }

declare class Foo { static bar: number; }

// Options: ["always"]
declare class Foo { static bar : number; }

class X { +foo: string }

class X { static +foo: string }

// Options: ["always"]
class X { +foo : string }

// Options: ["always"]
class X { static +foo : string }

type X = { foo: string }

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

type X = { foo?: string }

type X = { foo   ?: string }

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

type X = { +foo: string }

type X = { +foo?: string }

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

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

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

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

// Options: ["always"]
type X = { +[a : b] : c }

// Options: ["never"]
type X = { +[a:b]:c }

// Options: ["always"]
type X = { [a : (b)] : (c) }

// Options: ["never"]
type X = { [a:(b)]:(c) }

// Options: ["never"]
const x = ({}:{})

// Options: ["always"]
const x = ({} :{})

// Options: ["never"]
((x): string)

// Options: ["always"]
((x) : string)
```


### type-id-match

Enforces a consistent naming pattern for type aliases.

#### Options

This rule needs a text RegExp to operate with Its signature is as follows:

```js
{
    "rules": {
        "flowtype/type-id-match": [
            2,
            "^([A-Z][a-z0-9]*)+Type$"
        ]
    }
}
```

`'^([A-Z][a-z0-9]*)+Type$'` is the default pattern.

The following patterns are considered problems:

```js
type foo = {};
// Message: Type identifier 'foo' does not match pattern '/^([A-Z][a-z0-9]*)+Type$/'.

// Options: ["^foo$"]
type FooType = {};
// Message: Type identifier 'FooType' does not match pattern '/^foo$/'.
```

The following patterns are not considered problems:

```js
type FooType = {};

// Options: ["^foo$"]
type foo = {};
```


### union-intersection-spacing

_The `--fix` option on the command line automatically fixes problems reported by this rule._

Enforces consistent spacing around union and intersection type separators (`|` and `&`).

This rule takes one argument. If it is `'always'` then a problem is raised when there is no space around the separator. If it is `'never'` then a problem is raised when there is a space around the separator.

The default value is `'always'`.

The following patterns are considered problems:

```js
type X = string| number;
// Message: There must be a space before union type annotation separator

// Options: ["always"]
type X = string| number;
// Message: There must be a space before union type annotation separator

type X = string |number;
// Message: There must be a space after union type annotation separator

type X = string|number;
// Message: There must be a space before union type annotation separator
// Message: There must be a space after union type annotation separator

type X = {x: string}|{y: number};
// Message: There must be a space before union type annotation separator
// Message: There must be a space after union type annotation separator

type X = string | number |boolean;
// Message: There must be a space after union type annotation separator

type X = string|number|boolean;
// Message: There must be a space before union type annotation separator
// Message: There must be a space after union type annotation separator
// Message: There must be a space before union type annotation separator
// Message: There must be a space after union type annotation separator

type X = (string)| number;
// Message: There must be a space before union type annotation separator

type X = ((string))|(number | foo);
// Message: There must be a space before union type annotation separator
// Message: There must be a space after union type annotation separator

// Options: ["never"]
type X = string |number;
// Message: There must be no space before union type annotation separator

// Options: ["never"]
type X = string| number;
// Message: There must be no space after union type annotation separator

type X = string& number;
// Message: There must be a space before intersection type annotation separator

// Options: ["always"]
type X = string& number;
// Message: There must be a space before intersection type annotation separator

type X = string &number;
// Message: There must be a space after intersection type annotation separator

type X = {x: string}&{y: number};
// Message: There must be a space before intersection type annotation separator
// Message: There must be a space after intersection type annotation separator

type X = string&number;
// Message: There must be a space before intersection type annotation separator
// Message: There must be a space after intersection type annotation separator

type X = string & number &boolean;
// Message: There must be a space after intersection type annotation separator

type X = string&number&boolean;
// Message: There must be a space before intersection type annotation separator
// Message: There must be a space after intersection type annotation separator
// Message: There must be a space before intersection type annotation separator
// Message: There must be a space after intersection type annotation separator

type X = (string)& number;
// Message: There must be a space before intersection type annotation separator

type X = ((string))&(number & foo);
// Message: There must be a space before intersection type annotation separator
// Message: There must be a space after intersection type annotation separator

// Options: ["never"]
type X = string &number;
// Message: There must be no space before intersection type annotation separator

// Options: ["never"]
type X = string& number;
// Message: There must be no space after intersection type annotation separator
```

The following patterns are not considered problems:

```js
type X = string | number;

type X = string | number | boolean;

type X = (string) | number;

type X = ((string)) | (number | foo);

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

type X =
| string
| number

function x() {
type X =
| string
| number
}

type X = string & number;

type X = string & number & boolean;

type X = (string) & number;

type X = ((string)) & (number & foo);

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

type X =
& string
& number

function x() {
type X =
& string
& number
}
```


### use-flow-type

Marks Flow [type alias](https://flowtype.org/docs/type-aliases.html) declarations as used.

Used to suppress [`no-unused-vars`](http://eslint.org/docs/rules/no-unused-vars) errors that are triggered by type aliases.

The following patterns are not considered problems:

```js
declare class A {}
// Additional rules: {"no-unused-vars":1}

declare function A(): Y
// Additional rules: {"no-unused-vars":1}

declare module A {}
// Additional rules: {"no-unused-vars":1}

declare module A { declare var a: Y }
// Additional rules: {"no-unused-vars":1}

declare var A: Y
// Additional rules: {"no-unused-vars":1}

import type A from "a"; (function<T: A>(): T {})
// Additional rules: {"no-unused-vars":1}

(function<T: A>(): T {}); import type A from "a"
// Additional rules: {"no-unused-vars":1}

import type {A} from "a"; (function<T: A>(): T {})
// Additional rules: {"no-unused-vars":1}

(function<T: A>(): T {}); import type {A} from "a"
// Additional rules: {"no-unused-vars":1}

(function<T: A>(): T {}); import type {a as A} from "a"
// Additional rules: {"no-unused-vars":1}

type A = {}; function x<Y: A>(i: Y) { i }; x()
// Additional rules: {"no-unused-vars":1}

function x<Y: A>(i: Y) { i }; type A = {}; x()
// Additional rules: {"no-unused-vars":1}

type A = {}; function x<Y: A.B.C>(i: Y) { i }; x()
// Additional rules: {"no-unused-vars":1}

function x<Y: A.B.C>(i: Y) { i }; type A = {}; x()
// Additional rules: {"no-unused-vars":1}
```


### valid-syntax

**Deprecated** Babylon (the Babel parser) v6.10.0 fixes parsing of the invalid syntax this plugin warned against.

Checks for simple Flow syntax errors.

