feat(eslint-plugin): add consistent-type-imports rule (#2367)

Author: ota-meshi

Diff for: packages/eslint-plugin/README.md

@@ -106,6 +106,7 @@ Pro Tip: For larger codebases you may want to consider splitting our linting int
 | [`@typescript-eslint/class-literal-property-style`](./docs/rules/class-literal-property-style.md)                     | Ensures that literals on classes are exposed in a consistent style                                                      |                    | :wrench: |                   |
 | [`@typescript-eslint/consistent-type-assertions`](./docs/rules/consistent-type-assertions.md)                         | Enforces consistent usage of type assertions                                                                            |                    |          |                   |
 | [`@typescript-eslint/consistent-type-definitions`](./docs/rules/consistent-type-definitions.md)                       | Consistent with type definition either `interface` or `type`                                                            |                    | :wrench: |                   |
+| [`@typescript-eslint/consistent-type-imports`](./docs/rules/consistent-type-imports.md)                               | Enforces consistent usage of type imports                                                                               |                    | :wrench: |                   |
 | [`@typescript-eslint/explicit-function-return-type`](./docs/rules/explicit-function-return-type.md)                   | Require explicit return types on functions and class methods                                                            |                    |          |                   |
 | [`@typescript-eslint/explicit-member-accessibility`](./docs/rules/explicit-member-accessibility.md)                   | Require explicit accessibility modifiers on class properties and methods                                                |                    | :wrench: |                   |
 | [`@typescript-eslint/explicit-module-boundary-types`](./docs/rules/explicit-module-boundary-types.md)                 | Require explicit return and argument types on exported functions' and classes' public class methods                     | :heavy_check_mark: |          |                   |

Diff for: packages/eslint-plugin/docs/rules/consistent-type-imports.md

@@ -0,0 +1,64 @@
+# Enforces consistent usage of type imports (`consistent-type-imports`)
+
+TypeScript 3.8 added support for type-only imports.
+Type-only imports allow you to specify that an import can only be used in a type location, allowing certain optimizations within compilers.
+
+## Rule Details
+
+This rule aims to standardize the use of type imports style across the codebase.
+
+## Options
+
+```ts
+type Options = {
+  prefer: 'type-imports' | 'no-type-imports';
+  disallowTypeAnnotations: boolean;
+};
+
+const defaultOptions: Options = {
+  prefer: 'type-imports',
+  disallowTypeAnnotations: true,
+};
+```
+
+### `prefer`
+
+This option defines the expected import kind for type-only imports. Valid values for `prefer` are:
+
+- `type-imports` will enforce that you always use `import type Foo from '...'`. It is default.
+- `no-type-imports` will enforce that you always use `import Foo from '...'`.
+
+Examples of **correct** code with `{prefer: 'type-imports'}`, and **incorrect** code with `{prefer: 'no-type-imports'}`.
+
+```ts
+import type { Foo } from 'Foo';
+import type Bar from 'Bar';
+type T = Foo;
+const x: Bar = 1;
+```
+
+Examples of **incorrect** code with `{prefer: 'type-imports'}`, and **correct** code with `{prefer: 'no-type-imports'}`.
+
+```ts
+import { Foo } from 'Foo';
+import Bar from 'Bar';
+type T = Foo;
+const x: Bar = 1;
+```
+
+### `disallowTypeAnnotations`
+
+If `true`, type imports in type annotations (`import()`) is not allowed.
+Default is `true`.
+
+Examples of **incorrect** code with `{disallowTypeAnnotations: true}`.
+
+```ts
+type T = import('Foo').Foo;
+const x: import('Bar') = 1;
+```
+
+## When Not To Use It
+
+- If you are not using TypeScript 3.8 (or greater), then you will not be able to use this rule, as type-only imports are not allowed.
+- If you specifically want to use both import kinds for stylistic reasons, you can disable this rule.

Diff for: packages/eslint-plugin/src/configs/all.ts

@@ -18,6 +18,7 @@ export = {
     '@typescript-eslint/comma-spacing': 'error',
     '@typescript-eslint/consistent-type-assertions': 'error',
     '@typescript-eslint/consistent-type-definitions': 'error',
+    '@typescript-eslint/consistent-type-imports': 'error',
     'default-param-last': 'off',
     '@typescript-eslint/default-param-last': 'error',
     'dot-notation': 'off',