noUselessTypeConstraint

Diagnostic Category: lint/complexity/noUselessTypeConstraint

TypeScript and TSX

Since: v1.0.0

Sources:

Same as: @typescript-eslint/no-unnecessary-type-constraint

Disallow using any or unknown as type constraint.

Generic type parameters (<T>) in TypeScript may be constrained with extends. A supplied type must then be a subtype of the supplied constraint. All types are subtypes of any and unknown. It is thus useless to extend from any or unknown.

Examples

Invalid

interface FooAny<T extends any> {}

code-block.ts:1:20 lint/complexity/noUselessTypeConstraint  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Constraining a type parameter to any or unknown is useless.
  
  > 1 │ interface FooAny<T extends any> {}
      │                    ^^^^^^^^^^^
    2 │ 
  
  ℹ All types are subtypes of any and unknown.
  
  ℹ Safe fix: Remove the constraint.
  
    1 │ interface·FooAny<T·extends·any>·{}
      │                   ------------

type BarAny<T extends any> = {};

code-block.ts:1:15 lint/complexity/noUselessTypeConstraint  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Constraining a type parameter to any or unknown is useless.
  
  > 1 │ type BarAny<T extends any> = {};
      │               ^^^^^^^^^^^
    2 │ 
  
  ℹ All types are subtypes of any and unknown.
  
  ℹ Safe fix: Remove the constraint.
  
    1 │ type·BarAny<T·extends·any>·=·{};
      │              ------------

class BazAny<T extends any> {
}

code-block.ts:1:16 lint/complexity/noUselessTypeConstraint  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Constraining a type parameter to any or unknown is useless.
  
  > 1 │ class BazAny<T extends any> {
      │                ^^^^^^^^^^^
    2 │ }
    3 │ 
  
  ℹ All types are subtypes of any and unknown.
  
  ℹ Safe fix: Remove the constraint.
  
    1 │ class·BazAny<T·extends·any>·{
      │               ------------

class BazAny {
  quxAny<U extends any>() {}
}

code-block.ts:2:12 lint/complexity/noUselessTypeConstraint  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Constraining a type parameter to any or unknown is useless.
  
    1 │ class BazAny {
  > 2 │   quxAny<U extends any>() {}
      │            ^^^^^^^^^^^
    3 │ }
    4 │ 
  
  ℹ All types are subtypes of any and unknown.
  
  ℹ Safe fix: Remove the constraint.
  
    2 │ ··quxAny<U·extends·any>()·{}
      │           ------------

const QuuxAny = <T extends any>() => {};

code-block.ts:1:20 lint/complexity/noUselessTypeConstraint  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Constraining a type parameter to any or unknown is useless.
  
  > 1 │ const QuuxAny = <T extends any>() => {};
      │                    ^^^^^^^^^^^
    2 │ 
  
  ℹ All types are subtypes of any and unknown.
  
  ℹ Safe fix: Remove the constraint.
  
    1 │ const·QuuxAny·=·<T·extends·any>()·=>·{};
      │                   ------------

function QuuzAny<T extends any>() {}

code-block.ts:1:20 lint/complexity/noUselessTypeConstraint  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Constraining a type parameter to any or unknown is useless.
  
  > 1 │ function QuuzAny<T extends any>() {}
      │                    ^^^^^^^^^^^
    2 │ 
  
  ℹ All types are subtypes of any and unknown.
  
  ℹ Safe fix: Remove the constraint.
  
    1 │ function·QuuzAny<T·extends·any>()·{}
      │                   ------------

interface FooUnknown<T extends unknown> {}

code-block.ts:1:24 lint/complexity/noUselessTypeConstraint  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Constraining a type parameter to any or unknown is useless.
  
  > 1 │ interface FooUnknown<T extends unknown> {}
      │                        ^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ All types are subtypes of any and unknown.
  
  ℹ Safe fix: Remove the constraint.
  
    1 │ interface·FooUnknown<T·extends·unknown>·{}
      │                       ----------------

type BarUnknown<T extends unknown> = {};

code-block.ts:1:19 lint/complexity/noUselessTypeConstraint  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Constraining a type parameter to any or unknown is useless.
  
  > 1 │ type BarUnknown<T extends unknown> = {};
      │                   ^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ All types are subtypes of any and unknown.
  
  ℹ Safe fix: Remove the constraint.
  
    1 │ type·BarUnknown<T·extends·unknown>·=·{};
      │                  ----------------

class BazUnknown<T extends unknown> {
}
```ts,expect_diagnostic
class BazUnknown {
  quxUnknown<U extends unknown>() {}
}

code-block.ts:3:4 parse ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ unterminated template literal
  
    1 │ class BazUnknown<T extends unknown> {
    2 │ }
  > 3 │ ```ts,expect_diagnostic
      │    ^^^^^^^^^^^^^^^^^^^^
  > 4 │ class BazUnknown {
  > 5 │   quxUnknown<U extends unknown>() {}
  > 6 │ }
  > 7 │ 
      │

const QuuxUnknown = <T extends unknown>() => {};

code-block.ts:1:24 lint/complexity/noUselessTypeConstraint  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Constraining a type parameter to any or unknown is useless.
  
  > 1 │ const QuuxUnknown = <T extends unknown>() => {};
      │                        ^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ All types are subtypes of any and unknown.
  
  ℹ Safe fix: Remove the constraint.
  
    1 │ const·QuuxUnknown·=·<T·extends·unknown>()·=>·{};
      │                       ----------------

function QuuzUnknown<T extends unknown>() {}

code-block.ts:1:24 lint/complexity/noUselessTypeConstraint  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Constraining a type parameter to any or unknown is useless.
  
  > 1 │ function QuuzUnknown<T extends unknown>() {}
      │                        ^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ All types are subtypes of any and unknown.
  
  ℹ Safe fix: Remove the constraint.
  
    1 │ function·QuuzUnknown<T·extends·unknown>()·{}
      │                       ----------------

Valid

interface Foo<T> {}

type Bar<T> = {};

noUselessTypeConstraint

Examples

Invalid

Valid

Related links