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noUselessTypeConstraint (since v1.0.0)

Diagnostic Category: lint/complexity/noUselessTypeConstraint

Sources:

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

Section titled Examples

Invalid

Section titled Invalid
interface FooAny<T extends any> {}
complexity/noUselessTypeConstraint.js: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> = {};
complexity/noUselessTypeConstraint.js: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> {
}
complexity/noUselessTypeConstraint.js: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>() {}
}
complexity/noUselessTypeConstraint.js: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>() => {};
complexity/noUselessTypeConstraint.js: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>() {}
complexity/noUselessTypeConstraint.js: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> {}
complexity/noUselessTypeConstraint.js: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> = {};
complexity/noUselessTypeConstraint.js: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>() {}
}
complexity/noUselessTypeConstraint.js: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>() => {};
complexity/noUselessTypeConstraint.js: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>() {}
complexity/noUselessTypeConstraint.js: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

Section titled Valid
interface Foo<T> {}


type Bar<T> = {};
Section titled Related links