Flow: Infer string enum from the result of string concatenation

[dszakallas]

Currently flow cannot infer that the result of string concatenation is a string enum value:

type command = 'go_in' | 'go_out'

const com1: command = 'go_in' // OK
const com2: command = 'go_' + 'in' // Error
const createCommand = (dir: 'in' | 'out'): command => `go_${dir}` // Error

Demo

[vkurchatkin]

I'd say that while something like this is possible, it's out of scope of Flow.