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

BREAKING CHANGE: Merges both no-angle-bracket-type-assertion and no-object-literal-type-assertion into one rule
typescript-eslint · Jul 25, 2019 · 92e98de · 92e98de
1 parent 15191bb
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diff --git a/packages/eslint-plugin/README.md b/packages/eslint-plugin/README.md
@@ -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: |          |                   |
@@ -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: |          |                   |
@@ -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`                                                                                                                            |                    |          |                   |

diff --git a/packages/eslint-plugin/ROADMAP.md b/packages/eslint-plugin/ROADMAP.md
@@ -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]                                |
@@ -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`      |
@@ -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
@@ -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
@@ -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

diff --git a/packages/eslint-plugin/docs/rules/consistent-type-assertions.md b/packages/eslint-plugin/docs/rules/consistent-type-assertions.md
@@ -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/)
diff --git a/packages/eslint-plugin/docs/rules/no-angle-bracket-type-assertion.md b/packages/eslint-plugin/docs/rules/no-angle-bracket-type-assertion.md
diff --git a/packages/eslint-plugin/docs/rules/no-object-literal-type-assertion.md b/packages/eslint-plugin/docs/rules/no-object-literal-type-assertion.md
diff --git a/packages/eslint-plugin/src/configs/all.json b/packages/eslint-plugin/src/configs/all.json
@@ -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",
@@ -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",
@@ -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",

diff --git a/packages/eslint-plugin/src/configs/base.json b/packages/eslint-plugin/src/configs/base.json
@@ -3,5 +3,7 @@
   "parserOptions": {
     "sourceType": "module"
   },
-  "plugins": ["@typescript-eslint"]
+  "plugins": [
+    "@typescript-eslint"
+  ]
 }
diff --git a/packages/eslint-plugin/src/configs/recommended.json b/packages/eslint-plugin/src/configs/recommended.json
@@ -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",
@@ -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",