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Merged
merged 8 commits into from
Jul 25, 2019
Merged

feat(eslint-plugin)!: add rule consistent-type-assertions #731

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720b624
feat(eslint-plugin): add rule `consistent-type-assertions`
bradzacher Jul 20, 2019
a0d5762
chore: remove deprecated rules, update readme
bradzacher Jul 22, 2019
ca96941
Merge branch 'master' into consistent-type-assertions
bradzacher Jul 22, 2019
d118613
fix: update recommended so lint passes
bradzacher Jul 24, 2019
cb859a1
Merge branch 'master' into consistent-type-assertions
bradzacher Jul 24, 2019
ed22138
Merge branch 'master' into consistent-type-assertions
bradzacher Jul 24, 2019
b123512
Merge branch 'master' into consistent-type-assertions
bradzacher Jul 24, 2019
162e38d
Merge branch 'master' into consistent-type-assertions
bradzacher Jul 24, 2019
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3 changes: 1 addition & 2 deletions packages/eslint-plugin/README.md
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Expand Up @@ -130,6 +130,7 @@ Then you should add `airbnb` (or `airbnb-base`) to your `extends` section of `.e
| [`@typescript-eslint/ban-types`](./docs/rules/ban-types.md) | Enforces that types will not to be used | :heavy_check_mark: | :wrench: | |
| [`@typescript-eslint/camelcase`](./docs/rules/camelcase.md) | Enforce camelCase naming convention | :heavy_check_mark: | | |
| [`@typescript-eslint/class-name-casing`](./docs/rules/class-name-casing.md) | Require PascalCased class and interface names | :heavy_check_mark: | | |
| [`@typescript-eslint/consistent-type-assertions`](./docs/rules/consistent-type-assertions.md) | Enforces consistent usage of type assertions. | :heavy_check_mark: | | |
| [`@typescript-eslint/consistent-type-definitions`](./docs/rules/consistent-type-definitions.md) | Consistent with type definition either `interface` or `type` | | :wrench: | |
| [`@typescript-eslint/explicit-function-return-type`](./docs/rules/explicit-function-return-type.md) | Require explicit return types on functions and class methods | :heavy_check_mark: | | |
| [`@typescript-eslint/explicit-member-accessibility`](./docs/rules/explicit-member-accessibility.md) | Require explicit accessibility modifiers on class properties and methods | :heavy_check_mark: | | |
Expand All @@ -140,7 +141,6 @@ Then you should add `airbnb` (or `airbnb-base`) to your `extends` section of `.e
| [`@typescript-eslint/member-delimiter-style`](./docs/rules/member-delimiter-style.md) | Require a specific member delimiter style for interfaces and type literals | :heavy_check_mark: | :wrench: | |
| [`@typescript-eslint/member-naming`](./docs/rules/member-naming.md) | Enforces naming conventions for class members by visibility | | | |
| [`@typescript-eslint/member-ordering`](./docs/rules/member-ordering.md) | Require a consistent member declaration order | | | |
| [`@typescript-eslint/no-angle-bracket-type-assertion`](./docs/rules/no-angle-bracket-type-assertion.md) | Enforces the use of `as Type` assertions instead of `<Type>` assertions | :heavy_check_mark: | | |
| [`@typescript-eslint/no-array-constructor`](./docs/rules/no-array-constructor.md) | Disallow generic `Array` constructors | :heavy_check_mark: | :wrench: | |
| [`@typescript-eslint/no-empty-function`](./docs/rules/no-empty-function.md) | Disallow empty functions | | | |
| [`@typescript-eslint/no-empty-interface`](./docs/rules/no-empty-interface.md) | Disallow the declaration of empty interfaces | :heavy_check_mark: | | |
Expand All @@ -155,7 +155,6 @@ Then you should add `airbnb` (or `airbnb-base`) to your `extends` section of `.e
| [`@typescript-eslint/no-misused-promises`](./docs/rules/no-misused-promises.md) | Avoid using promises in places not designed to handle them | | | :thought_balloon: |
| [`@typescript-eslint/no-namespace`](./docs/rules/no-namespace.md) | Disallow the use of custom TypeScript modules and namespaces | :heavy_check_mark: | | |
| [`@typescript-eslint/no-non-null-assertion`](./docs/rules/no-non-null-assertion.md) | Disallows non-null assertions using the `!` postfix operator | :heavy_check_mark: | | |
| [`@typescript-eslint/no-object-literal-type-assertion`](./docs/rules/no-object-literal-type-assertion.md) | Forbids an object literal to appear in a type assertion expression | :heavy_check_mark: | | |
| [`@typescript-eslint/no-parameter-properties`](./docs/rules/no-parameter-properties.md) | Disallow the use of parameter properties in class constructors | :heavy_check_mark: | | |
| [`@typescript-eslint/no-require-imports`](./docs/rules/no-require-imports.md) | Disallows invocation of `require()` | | | |
| [`@typescript-eslint/no-this-alias`](./docs/rules/no-this-alias.md) | Disallow aliasing `this` | | | |
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7 changes: 3 additions & 4 deletions packages/eslint-plugin/ROADMAP.md
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Expand Up @@ -71,7 +71,7 @@
| [`no-invalid-this`] | 🌟 | [`no-invalid-this`][no-invalid-this] |
| [`no-misused-new`] | ✅ | [`@typescript-eslint/no-misused-new`] |
| [`no-null-keyword`] | 🔌 | [`no-null/no-null`] (doesn’t handle `null` type) |
| [`no-object-literal-type-assertion`] | ✅ | [`@typescript-eslint/no-object-literal-type-assertion`] |
| [`no-object-literal-type-assertion`] | ✅ | [`@typescript-eslint/consistent-type-assertions`] |
| [`no-return-await`] | 🌟 | [`no-return-await`][no-return-await] |
| [`no-shadowed-variable`] | 🌟 | [`no-shadow`][no-shadow] |
| [`no-sparse-arrays`] | 🌟 | [`no-sparse-arrays`][no-sparse-arrays] |
Expand Down Expand Up @@ -155,7 +155,7 @@
| [`newline-before-return`] | 🌟 | [`padding-line-between-statements`][padding-line-between-statements] <sup>[1]</sup> |
| [`newline-per-chained-call`] | 🌟 | [`newline-per-chained-call`][newline-per-chained-call] |
| [`new-parens`] | 🌟 | [`new-parens`][new-parens] |
| [`no-angle-bracket-type-assertion`] | ✅ | [`@typescript-eslint/no-angle-bracket-type-assertion`] |
| [`no-angle-bracket-type-assertion`] | ✅ | [`@typescript-eslint/consistent-type-assertions`] |
| [`no-boolean-literal-compare`] | 🛑 | N/A |
| [`no-consecutive-blank-lines`] | 🌟 | [`no-multiple-empty-lines`][no-multiple-empty-lines] |
| [`no-irregular-whitespace`] | 🌟 | [`no-irregular-whitespace`][no-irregular-whitespace] with `skipStrings: false` |
Expand Down Expand Up @@ -579,6 +579,7 @@ Relevant plugins: [`chai-expect-keywords`](https://github.com/gavinaiken/eslint-
[`@typescript-eslint/await-thenable`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/await-thenable.md
[`@typescript-eslint/ban-types`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/ban-types.md
[`@typescript-eslint/ban-ts-ignore`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/ban-ts-ignore.md
[`@typescript-eslint/consistent-type-assertions`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/consistent-type-assertions.md
[`@typescript-eslint/consistent-type-definitions`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/consistent-type-definitions.md
[`@typescript-eslint/explicit-member-accessibility`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/explicit-member-accessibility.md
[`@typescript-eslint/member-ordering`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/member-ordering.md
Expand All @@ -597,7 +598,6 @@ Relevant plugins: [`chai-expect-keywords`](https://github.com/gavinaiken/eslint-
[`@typescript-eslint/typedef`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/typedef.md
[`@typescript-eslint/unified-signatures`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/unified-signatures.md
[`@typescript-eslint/no-misused-new`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-misused-new.md
[`@typescript-eslint/no-object-literal-type-assertion`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-object-literal-type-assertion.md
[`@typescript-eslint/no-this-alias`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-this-alias.md
[`@typescript-eslint/no-extraneous-class`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-extraneous-class.md
[`@typescript-eslint/no-unused-vars`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-unused-vars.md
Expand All @@ -608,7 +608,6 @@ Relevant plugins: [`chai-expect-keywords`](https://github.com/gavinaiken/eslint-
[`@typescript-eslint/array-type`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/array-type.md
[`@typescript-eslint/class-name-casing`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/class-name-casing.md
[`@typescript-eslint/interface-name-prefix`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/interface-name-prefix.md
[`@typescript-eslint/no-angle-bracket-type-assertion`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-angle-bracket-type-assertion.md
[`@typescript-eslint/no-parameter-properties`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-parameter-properties.md
[`@typescript-eslint/member-delimiter-style`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/member-delimiter-style.md
[`@typescript-eslint/prefer-for-of`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/prefer-for-of.md
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79 changes: 79 additions & 0 deletions packages/eslint-plugin/docs/rules/consistent-type-assertions.md
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@@ -0,0 +1,79 @@
# Enforces consistent usage of type assertions. (consistent-type-assertions)

## Rule Details

This rule aims to standardise the use of type assertion style across the codebase.

Type assertions are also commonly referred as "type casting" in TypeScript (even though it is technically slightly different to what is understood by type casting in other languages), so you can think of type assertions and type casting referring to the same thing. It is essentially you saying to the TypeScript compiler, "in this case, I know better than you!".

## Options

```ts
type Options =
| {
assertionStyle: 'as' | 'angle-bracket';
objectLiteralTypeAssertions: 'allow' | 'allow-as-parameter' | 'never';
}
| {
assertionStyle: 'never';
};

const defaultOptions: Options = {
assertionStyle: 'as',
objectLiteralTypeAssertions: 'allow',
};
```

### assertionStyle

This option defines the expected assertion style. Valid values for `assertionStyle` are:

- `as` will enforce that you always use `... as foo`.
- `angle-bracket` will enforce that you always use `<foo>...`
- `never` will enforce that you do not do any type assertions.

Most code bases will want to enforce not using `angle-bracket` style because it conflicts with JSX syntax, and is confusing when paired with with generic syntax.

Some codebases like to go for an extra level of type safety, and ban assertions altogether via the `never` option.

### objectLiteralTypeAssertions

Always prefer `const x: T = { ... };` to `const x = { ... } as T;` (or similar with angle brackets). The type assertion in the latter case is either unnecessary or will probably hide an error.

The compiler will warn for excess properties with this syntax, but not missing _required_ fields. For example: `const x: { foo: number } = {};` will fail to compile, but `const x = {} as { foo: number }` will succeed.

The const assertion `const x = { foo: 1 } as const`, introduced in TypeScript 3.4, is considered beneficial and is ignored by this option.

Examples of **incorrect** code for `{ assertionStyle: 'as', objectLiteralTypeAssertions: 'never' }` (and for `{ assertionStyle: 'as', objectLiteralTypeAssertions: 'allow-as-parameter' }`)

```ts
const x = { ... } as T;
```

Examples of **correct** code for `{ assertionStyle: 'as', objectLiteralTypeAssertions: 'never' }`.

```ts
const x: T = { ... };
const y = { ... } as any;
const z = { ... } as unknown;
```

Examples of **correct** code for `{ assertionStyle: 'as', objectLiteralTypeAssertions: 'allow-as-parameter' }`.

```ts
const x: T = { ... };
const y = { ... } as any;
const z = { ... } as unknown;
foo({ ... } as T);
new Clazz({ ... } as T);
function foo() { throw { bar: 5 } as Foo }
```

## When Not To Use It

If you do not want to enforce consistent type assertions.

## Compatibility

- TSLint: [no-angle-bracket-type-assertion](https://palantir.github.io/tslint/rules/no-angle-bracket-type-assertion/)
- TSLint: [no-object-literal-type-assertion](https://palantir.github.io/tslint/rules/no-object-literal-type-assertion/)
32 changes: 0 additions & 32 deletions packages/eslint-plugin/docs/rules/no-angle-bracket-type-assertion.md
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33 changes: 0 additions & 33 deletions packages/eslint-plugin/docs/rules/no-object-literal-type-assertion.md
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3 changes: 1 addition & 2 deletions packages/eslint-plugin/src/configs/all.json
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Expand Up @@ -9,6 +9,7 @@
"camelcase": "off",
"@typescript-eslint/camelcase": "error",
"@typescript-eslint/class-name-casing": "error",
"@typescript-eslint/consistent-type-assertions": "error",
"@typescript-eslint/consistent-type-definitions": "error",
"@typescript-eslint/explicit-function-return-type": "error",
"@typescript-eslint/explicit-member-accessibility": "error",
Expand All @@ -21,7 +22,6 @@
"@typescript-eslint/member-delimiter-style": "error",
"@typescript-eslint/member-naming": "error",
"@typescript-eslint/member-ordering": "error",
"@typescript-eslint/no-angle-bracket-type-assertion": "error",
"no-array-constructor": "off",
"@typescript-eslint/no-array-constructor": "error",
"@typescript-eslint/no-empty-function": "error",
Expand All @@ -39,7 +39,6 @@
"@typescript-eslint/no-misused-promises": "error",
"@typescript-eslint/no-namespace": "error",
"@typescript-eslint/no-non-null-assertion": "error",
"@typescript-eslint/no-object-literal-type-assertion": "error",
"@typescript-eslint/no-parameter-properties": "error",
"@typescript-eslint/no-require-imports": "error",
"@typescript-eslint/no-this-alias": "error",
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4 changes: 3 additions & 1 deletion packages/eslint-plugin/src/configs/base.json
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Expand Up @@ -3,5 +3,7 @@
"parserOptions": {
"sourceType": "module"
},
"plugins": ["@typescript-eslint"]
"plugins": [
"@typescript-eslint"
]
}
3 changes: 1 addition & 2 deletions packages/eslint-plugin/src/configs/recommended.json
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Expand Up @@ -11,13 +11,13 @@
"camelcase": "off",
"@typescript-eslint/camelcase": "error",
"@typescript-eslint/class-name-casing": "error",
"@typescript-eslint/consistent-type-assertions": "error",
"@typescript-eslint/explicit-function-return-type": "warn",
"@typescript-eslint/explicit-member-accessibility": "error",
"indent": "off",
"@typescript-eslint/indent": "error",
"@typescript-eslint/interface-name-prefix": "error",
"@typescript-eslint/member-delimiter-style": "error",
"@typescript-eslint/no-angle-bracket-type-assertion": "error",
"no-array-constructor": "off",
"@typescript-eslint/no-array-constructor": "error",
"@typescript-eslint/no-empty-interface": "error",
Expand All @@ -26,7 +26,6 @@
"@typescript-eslint/no-misused-new": "error",
"@typescript-eslint/no-namespace": "error",
"@typescript-eslint/no-non-null-assertion": "error",
"@typescript-eslint/no-object-literal-type-assertion": "error",
"@typescript-eslint/no-parameter-properties": "error",
"no-unused-vars": "off",
"@typescript-eslint/no-unused-vars": "warn",
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