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feat(eslint-plugin): split no-empty-object-type out from ban-types and no-empty-interfaces (typescript-eslint#8977)
* feat(eslint-plugin): split no-empty-object-type rule out from ban-types rule * Mention no-props * Update packages/eslint-plugin/docs/rules/no-empty-object-type.mdx Co-authored-by: Kirk Waiblinger <53019676+kirkwaiblinger@users.noreply.github.com> * Update packages/eslint-plugin/docs/rules/no-empty-object-type.mdx Co-authored-by: Kirk Waiblinger <53019676+kirkwaiblinger@users.noreply.github.com> * Allow in intersections, and touch up docs per suggestions * Update packages/eslint-plugin/docs/rules/no-empty-object-type.mdx Co-authored-by: Joshua Chen <sidachen2003@gmail.com> * Trimming * Update snapshots * Finish removing Record * Correct phrasing on Object * Merge with no-empty-interface * nit the tip * Explicit report message for interfaces * Add in-type-alias-with-name * Switched to more general allowWithName * snapshot -u * snapshot -u * Fixed up unit tests * Update packages/eslint-plugin/docs/rules/no-empty-object-type.mdx Co-authored-by: Kirk Waiblinger <kirk.waiblinger@gmail.com> * docs touchups from Kirk * replacedBy too --------- Co-authored-by: Kirk Waiblinger <53019676+kirkwaiblinger@users.noreply.github.com> Co-authored-by: Joshua Chen <sidachen2003@gmail.com> Co-authored-by: Kirk Waiblinger <kirk.waiblinger@gmail.com>
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‎packages/eslint-plugin/TSLINT_RULE_ALTERNATIVES.md

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@@ -24,7 +24,7 @@ It lists all TSLint rules along side rules from the ESLint ecosystem that are th
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| [`member-access`] | ✅ | [`@typescript-eslint/explicit-member-accessibility`] |
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| [`member-ordering`] | ✅ | [`@typescript-eslint/member-ordering`] |
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| [`no-any`] | ✅ | [`@typescript-eslint/no-explicit-any`] |
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| [`no-empty-interface`] | ✅ | [`@typescript-eslint/no-empty-interface`] |
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| [`no-empty-interface`] | ✅ | [`@typescript-eslint/no-empty-object-type`] |
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| [`no-import-side-effect`] | 🔌 | [`import/no-unassigned-import`] |
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| [`no-inferrable-types`] | ✅ | [`@typescript-eslint/no-inferrable-types`] |
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| [`no-internal-module`] | ✅ | [`@typescript-eslint/prefer-namespace-keyword`] |
@@ -604,7 +604,7 @@ Relevant plugins: [`chai-expect-keywords`](https://github.com/gavinaiken/eslint-
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[`@typescript-eslint/member-ordering`]: https://typescript-eslint.io/rules/member-ordering
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[`@typescript-eslint/method-signature-style`]: https://typescript-eslint.io/rules/method-signature-style
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[`@typescript-eslint/no-explicit-any`]: https://typescript-eslint.io/rules/no-explicit-any
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[`@typescript-eslint/no-empty-interface`]: https://typescript-eslint.io/rules/no-empty-interface
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[`@typescript-eslint/no-empty-object-type`]: https://typescript-eslint.io/rules/no-empty-object-type
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[`@typescript-eslint/no-implied-eval`]: https://typescript-eslint.io/rules/no-implied-eval
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[`@typescript-eslint/no-inferrable-types`]: https://typescript-eslint.io/rules/no-inferrable-types
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[`@typescript-eslint/prefer-namespace-keyword`]: https://typescript-eslint.io/rules/prefer-namespace-keyword

‎packages/eslint-plugin/docs/rules/ban-types.mdx

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// use safer object types
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const lowerObj: Object = {};
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const capitalObj: Object = { a: 'string' };
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const curly1: {} = 1;
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const curly2: {} = { a: 'string' };
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```
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</TabItem>
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// use safer object types
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const lowerObj: object = {};
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const capitalObj: { a: string } = { a: 'string' };
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const curly1: number = 1;
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const curly2: Record<'a', string> = { a: 'string' };
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```
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</TabItem>
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The default options provide a set of "best practices", intended to provide safety and standardization in your codebase:
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- Don't use the upper-case primitive types, you should use the lower-case types for consistency.
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- Don't use the upper-case primitive types or `Object`, you should use the lower-case types for consistency.
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- Avoid the `Function` type, as it provides little safety for the following reasons:
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- It provides no type safety when calling the value, which means it's easy to provide the wrong arguments.
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- It accepts class declarations, which will fail when called, as they are called without the `new` keyword.
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- Avoid the `Object` and `{}` types, as they mean "any non-nullish value".
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- This is a point of confusion for many developers, who think it means "any object type".
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- See [this comment for more information](https://github.com/typescript-eslint/typescript-eslint/issues/2063#issuecomment-675156492).
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<details>
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<summary>Default Options</summary>
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If your project is a rare one that intentionally deals with the class equivalents of primitives, it might not be worthwhile to enable the default `ban-types` options.
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You might consider using [ESLint disable comments](https://eslint.org/docs/latest/use/configure/rules#using-configuration-comments-1) for those specific situations instead of completely disabling this rule.
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## Related To
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- [`no-empty-object-type`](./no-empty-object-type.mdx)

‎packages/eslint-plugin/docs/rules/no-empty-interface.mdx

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>
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> See **https://typescript-eslint.io/rules/no-empty-interface** for documentation.
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:::danger Deprecated
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This rule has been deprecated in favour of the more comprehensive [`@typescript-eslint/no-empty-object-type`](./no-empty-object-type.mdx) rule.
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:::
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An empty interface in TypeScript does very little: any non-nullable value is assignable to `{}`.
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Using an empty interface is often a sign of programmer error, such as misunderstanding the concept of `{}` or forgetting to fill in fields.
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## When Not To Use It
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If you don't care about having empty/meaningless interfaces, then you will not need this rule.
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## Related To
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- [`no-empty-object-type`](./no-empty-object-type.mdx)

‎packages/eslint-plugin/docs/rules/no-empty-object-type.mdx

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---
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description: 'Disallow accidentally using the "empty object" type.'
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---
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import Tabs from '@theme/Tabs';
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import TabItem from '@theme/TabItem';
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> 🛑 This file is source code, not the primary documentation location! 🛑
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>
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> See **https://typescript-eslint.io/rules/no-empty-object-type** for documentation.
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The `{}`, or "empty object" type in TypeScript is a common source of confusion for developers unfamiliar with TypeScript's structural typing.
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`{}` represents any _non-nullish value_, including literals like `0` and `""`:
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```ts
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let anyNonNullishValue: {} = 'Intentionally allowed by TypeScript.';
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```
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Often, developers writing `{}` actually mean either:
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- `object`: representing any _object_ value
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- `unknown`: representing any value at all, including `null` and `undefined`
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In other words, the "empty object" type `{}` really means _"any value that is defined"_.
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That includes arrays, class instances, functions, and primitives such as `string` and `symbol`.
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To avoid confusion around the `{}` type allowing any _non-nullish value_, this rule bans usage of the `{}` type.
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That includes interfaces and object type aliases with no fields.
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:::tip
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If you do have a use case for an API allowing `{}`, you can always configure the [rule's options](#options), use an [ESLint disable comment](https://eslint.org/docs/latest/use/configure/rules#using-configuration-comments-1), or [disable the rule in your ESLint config](https://eslint.org/docs/latest/use/configure/rules#using-configuration-files-1).
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:::
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Note that this rule does not report on:
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- `{}` as a type constituent in an intersection type (e.g. types like TypeScript's built-in `type NonNullable<T> = T & {}`), as this can be useful in type system operations.
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- Interfaces that extend from multiple other interfaces.
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## Examples
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<Tabs>
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<TabItem value="❌ Incorrect">
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```ts
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let anyObject: {};
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let anyValue: {};
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interface AnyObjectA {}
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interface AnyValueA {}
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type AnyObjectB = {};
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type AnyValueB = {};
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```
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</TabItem>
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<TabItem value="✅ Correct">
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```ts
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let anyObject: object;
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let anyValue: unknown;
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type AnyObjectA = object;
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type AnyValueA = unknown;
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type AnyObjectB = object;
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type AnyValueB = unknown;
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let objectWith: { property: boolean };
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interface InterfaceWith {
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property: boolean;
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}
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type TypeWith = { property: boolean };
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```
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</TabItem>
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</Tabs>
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## Options
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By default, this rule flags both interfaces and object types.
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### `allowInterfaces`
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Whether to allow empty interfaces, as one of:
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- `'always'`: to always allow interfaces with no fields
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- `'never'` _(default)_: to never allow interfaces with no fields
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- `'with-single-extends'`: to allow empty interfaces that `extend` from a single base interface
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Examples of **correct** code for this rule with `{ allowInterfaces: 'with-single-extends' }`:
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```ts option='{ "allowInterfaces": "with-single-extends" }' showPlaygroundButton
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interface Base {
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value: boolean;
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}
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interface Derived extends Base {}
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```
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### `allowObjectTypes`
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Whether to allow empty object type literals, as one of:
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- `'always'`: to always allow object type literals with no fields
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- `'never'` _(default)_: to never allow object type literals with no fields
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### `allowWithName`
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A stringified regular expression to allow interfaces and object type aliases with the configured name.
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This can be useful if your existing code style includes a pattern of declaring empty types with `{}` instead of `object`.
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Examples of code for this rule with `{ allowWithName: 'Props$' }`:
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<Tabs>
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<TabItem value="❌ Incorrect">
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```ts option='{ "allowWithName": "Props$" }' showPlaygroundButton
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interface InterfaceValue {}
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type TypeValue = {};
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```
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</TabItem>
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<TabItem value="✅ Correct">
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```ts option='{ "allowWithName": "Props$" }' showPlaygroundButton
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interface InterfaceProps {}
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type TypeProps = {};
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```
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</TabItem>
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</Tabs>
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## When Not To Use It
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If your code commonly needs to represent the _"any non-nullish value"_ type, this rule may not be for you.
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Projects that extensively use type operations such as conditional types and mapped types oftentimes benefit from disabling this rule.
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## Further Reading
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- [Enhancement: [ban-types] Split the {} ban into a separate, better-phrased rule](https://github.com/typescript-eslint/typescript-eslint/issues/8700)
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- [The Empty Object Type in TypeScript](https://www.totaltypescript.com/the-empty-object-type-in-typescript)

‎packages/eslint-plugin/src/configs/all.ts

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'@typescript-eslint/no-dynamic-delete': 'error',
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'no-empty-function': 'off',
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'@typescript-eslint/no-empty-function': 'error',
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'@typescript-eslint/no-empty-interface': 'error',
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'@typescript-eslint/no-empty-object-type': 'error',
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'@typescript-eslint/no-explicit-any': 'error',
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'@typescript-eslint/no-extra-non-null-assertion': 'error',
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'@typescript-eslint/no-extraneous-class': 'error',

‎packages/eslint-plugin/src/configs/recommended-type-checked.ts

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'@typescript-eslint/no-base-to-string': 'error',
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'@typescript-eslint/no-duplicate-enum-values': 'error',
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'@typescript-eslint/no-duplicate-type-constituents': 'error',
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'@typescript-eslint/no-empty-object-type': 'error',
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'@typescript-eslint/no-explicit-any': 'error',
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'@typescript-eslint/no-extra-non-null-assertion': 'error',
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'@typescript-eslint/no-floating-promises': 'error',

‎packages/eslint-plugin/src/configs/recommended.ts

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'no-array-constructor': 'off',
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'@typescript-eslint/no-array-constructor': 'error',
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'@typescript-eslint/no-duplicate-enum-values': 'error',
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'@typescript-eslint/no-empty-object-type': 'error',
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'@typescript-eslint/no-explicit-any': 'error',
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'@typescript-eslint/no-extra-non-null-assertion': 'error',
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'@typescript-eslint/no-misused-new': 'error',

‎packages/eslint-plugin/src/configs/strict-type-checked.ts

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'@typescript-eslint/no-duplicate-enum-values': 'error',
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'@typescript-eslint/no-duplicate-type-constituents': 'error',
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'@typescript-eslint/no-dynamic-delete': 'error',
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'@typescript-eslint/no-empty-object-type': 'error',
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'@typescript-eslint/no-explicit-any': 'error',
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'@typescript-eslint/no-extra-non-null-assertion': 'error',
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'@typescript-eslint/no-extraneous-class': 'error',

‎packages/eslint-plugin/src/configs/strict.ts

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'@typescript-eslint/no-array-constructor': 'error',
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'@typescript-eslint/no-duplicate-enum-values': 'error',
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'@typescript-eslint/no-dynamic-delete': 'error',
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'@typescript-eslint/no-empty-object-type': 'error',
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'@typescript-eslint/no-explicit-any': 'error',
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'@typescript-eslint/no-extra-non-null-assertion': 'error',
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'@typescript-eslint/no-extraneous-class': 'error',

‎packages/eslint-plugin/src/configs/stylistic-type-checked.ts

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'@typescript-eslint/no-confusing-non-null-assertion': 'error',
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'no-empty-function': 'off',
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'@typescript-eslint/no-empty-function': 'error',
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'@typescript-eslint/no-empty-interface': 'error',
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'@typescript-eslint/no-inferrable-types': 'error',
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'@typescript-eslint/non-nullable-type-assertion-style': 'error',
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'@typescript-eslint/prefer-for-of': 'error',

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