redundantTypeConstituents

Reports union and intersection type constituents that are redundant or override other types.

✅ This rule is included in the ts logical presets.

Some types can override other types in a union or intersection, making certain constituents redundant. TypeScript’s set theory of types includes cases where a constituent type might be useless in the parent union or intersection.

Within | unions:

• any and unknown override all other union members
• never is dropped from unions (except in return type position)
• Primitive types like string override their literal types like "hello"

Within & intersections:

• any and never override all other intersection members
• unknown is dropped from intersections
• Literal types like "hello" override their primitive types like string

Examples

❌ Incorrect

type A = number | any;

type B = string | "literal";

type C = number & never;

type D = unknown & string;

✅ Correct

type A = number | string;

type B = "a" | "b";

type C = number & object;

type D = string & { brand: symbol };

Options

This rule is not configurable.

When Not To Use It

Some projects choose to occasionally include a redundant type constituent for documentation purposes. For example, some unions intentionally include a redundant string in unions containing unknown to indicate intent. You might consider using Flint disable comments and/or configuration file disables for those specific situations instead of completely disabling this rule.

Further Reading

• TypeScript Handbook: Union Types
• TypeScript Handbook: Intersection Types
• Wikipedia: Bottom Type
• Wikipedia: Top Type

Equivalents in Other Linters

• ESLint: @typescript-eslint/no-redundant-type-constituents
• Oxlint: typescript/no-redundant-type-constituents