IfNotAnyOrNever

// When `T` is a NOT `any` or `never` (like `string`) => Returns `IfNotAnyOrNever` branch
type A = IfNotAnyOrNever<string, 'VALID', 'IS_ANY', 'IS_NEVER'>;
//=> 'VALID'

// When `T` is `any` => Returns `IfAny` branch
type B = IfNotAnyOrNever<any, 'VALID', 'IS_ANY', 'IS_NEVER'>;
//=> 'IS_ANY'

// When `T` is `never` => Returns `IfNever` branch
type C = IfNotAnyOrNever<never, 'VALID', 'IS_ANY', 'IS_NEVER'>;
//=> 'IS_NEVER'

Note: Wrapping a tail-recursive type with IfNotAnyOrNever makes the implementation non-tail-recursive. To fix this, move the recursion into a helper type. Refer to the following example:

// When `T` is a NOT `any` or `never` (like `string`) => Returns `IfNotAnyOrNever` branch
type A = IfNotAnyOrNever<string, 'VALID', 'IS_ANY', 'IS_NEVER'>;
//=> 'VALID'

// When `T` is `any` => Returns `IfAny` branch
type B = IfNotAnyOrNever<any, 'VALID', 'IS_ANY', 'IS_NEVER'>;
//=> 'IS_ANY'

// When `T` is `never` => Returns `IfNever` branch
type C = IfNotAnyOrNever<never, 'VALID', 'IS_ANY', 'IS_NEVER'>;
//=> 'IS_NEVER'

Note: Wrapping a tail-recursive type with IfNotAnyOrNever makes the implementation non-tail-recursive. To fix this, move the recursion into a helper type. Refer to the following example:

import type {StringRepeat} from 'type-fest';

type NineHundredNinetyNineSpaces = StringRepeat<' ', 999>;

// The following implementation is not tail recursive
type TrimLeft<S extends string> = IfNotAnyOrNever<S, S extends ` ${infer R}` ? TrimLeft<R> : S>;

// Hence, instantiations with long strings will fail
// @ts-expect-error
type T1 = TrimLeft<NineHundredNinetyNineSpaces>;
//        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// Error: Type instantiation is excessively deep and possibly infinite.

// To fix this, move the recursion into a helper type
type TrimLeftOptimised<S extends string> = IfNotAnyOrNever<S, _TrimLeftOptimised<S>>;

type _TrimLeftOptimised<S extends string> = S extends ` ${infer R}` ? _TrimLeftOptimised<R> : S;

type T2 = TrimLeftOptimised<NineHundredNinetyNineSpaces>;
//=> ''

import type {StringRepeat} from 'type-fest';

type NineHundredNinetyNineSpaces = StringRepeat<' ', 999>;

// The following implementation is not tail recursive
type TrimLeft<S extends string> = IfNotAnyOrNever<S, S extends ` ${infer R}` ? TrimLeft<R> : S>;

// Hence, instantiations with long strings will fail
// @ts-expect-error
type T1 = TrimLeft<NineHundredNinetyNineSpaces>;
//        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// Error: Type instantiation is excessively deep and possibly infinite.

// To fix this, move the recursion into a helper type
type TrimLeftOptimised<S extends string> = IfNotAnyOrNever<S, _TrimLeftOptimised<S>>;

type _TrimLeftOptimised<S extends string> = S extends ` ${infer R}` ? _TrimLeftOptimised<R> : S;

type T2 = TrimLeftOptimised<NineHundredNinetyNineSpaces>;
//=> ''