$Compose/$ComposeReverse isn't a subtype of (...any) => any

[Bannerets]

Flow version: v0.102.0

// @flow
declare var c1: $Compose
;(c1: (...args: any) => any) // error
declare var c2: $ComposeReverse
;(c2: (...args: any) => any) // error

try flow

Actual behavior

I see the weird Cannot cast c1 to function type because function type [1] is incompatible with function type errors.

Expected behavior

$Compose behaves like a function, so I expect it to be a subtype of (...args: any) => any.

Also, If it will be fixed, it allows creation of $TupleReduce via $TupleMap:

Example

// @flow

declare function apply<Args, R>(f: (...Args) => R, ...args: Args): R
type _Apply = typeof apply
type Apply<Fn, Args> = $Call<_Apply, Fn, Args>

declare function reduce<Fn, A, T>(Fn, A, T): $Call<
  Apply<
    $Compose,
    $TupleMap<T, Fn>,
  >
, A>
type _Reduce = typeof reduce

export type Reduce<Fn, A, T> = $Call<_Reduce, Fn, A, T>

type MergeAll<T> = Reduce<<X, V>(V) => ((X) => ({...$Exact<X>, ...$Exact<V>})), {}, T>

declare function mergeAll<A>(A): MergeAll<A>

const x = mergeAll([{a: 1}, {b: 1}, {c: 1}])

;(x: {a: 1, b: 1, c: 1})

;(x: {a: 1, b: 1, c: '1'}) // error

try flow

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• Link to Try-Flow or Github repo: link

[SamChou19815]

Closing since support for these types is removed in 0.232