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96 lines
2.7 KiB
Text
96 lines
2.7 KiB
Text
---
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description: 'Disallow members of unions and intersections that do nothing or override type information.'
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---
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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-redundant-type-constituents** for documentation.
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## Rule Details
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Some types can override some other types ("constituents") in a union or intersection and/or be overridden by some other types.
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TypeScript's set theory of types includes cases where a constituent type might be useless in the parent union or intersection.
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Within `|` unions:
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- `any` and `unknown` "override" all other union members
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- `never` is dropped from unions in any position except when in a return type position
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- primitive types such as `string` "override" any of their literal types such as `""`
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Within `&` intersections:
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- `any` and `never` "override" all other intersection members
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- `unknown` is dropped from intersections
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- literal types "override" any primitive types in an intersection
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- literal types such as `""` "override" any of their primitive types such as `string`
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Examples of code for this rule:
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<!--tabs-->
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### ❌ Incorrect
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```ts
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type UnionAny = any | 'foo';
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type UnionUnknown = unknown | 'foo';
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type UnionNever = never | 'foo';
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type UnionBooleanLiteral = boolean | false;
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type UnionNumberLiteral = number | 1;
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type UnionStringLiteral = string | 'foo';
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type IntersectionAny = any & 'foo';
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type IntersectionUnknown = string & unknown;
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type IntersectionNever = string | never;
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type IntersectionBooleanLiteral = boolean & false;
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type IntersectionNumberLiteral = number & 1;
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type IntersectionStringLiteral = string & 'foo';
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```
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### ✅ Correct
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```ts
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type UnionAny = any;
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type UnionUnknown = unknown;
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type UnionNever = never;
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type UnionBooleanLiteral = boolean;
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type UnionNumberLiteral = number;
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type UnionStringLiteral = string;
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type IntersectionAny = any;
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type IntersectionUnknown = string;
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type IntersectionNever = string;
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type IntersectionBooleanLiteral = false;
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type IntersectionNumberLiteral = 1;
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type IntersectionStringLiteral = 'foo';
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type ReturnUnionNever = () => string | never;
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```
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## Options
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```jsonc
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// .eslintrc.json
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{
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"rules": {
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"@typescript-eslint/no-redundant-type-constituents": "warn"
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}
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}
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```
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This rule is not configurable.
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## Limitations
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This rule plays it safe and only works with bottom types, top types, and comparing literal types to primitive types.
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It also does not provide an auto-fixer just yet.
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## Further Reading
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- [Union Types](https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#union-types)
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- [Intersection Types](https://www.typescriptlang.org/docs/handbook/2/objects.html#intersection-types)
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- [Bottom Types](https://en.wikipedia.org/wiki/Bottom_type)
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- [Top Types](https://en.wikipedia.org/wiki/Top_type)
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