Fix #3274 and other features

[alfonsogarciacaro]

1. Fix Wrong behavior if --outDir is a prefix of project dir #3274: Output files are not put into outDir when this is a prefix of the project dir
2. Check Condition when manually parsing .fsproj in Fable packages. The condition is only evaluated if the property is one of the constants defined by Fable or user. Not sure if we will use this feature but I implemented it in case we decide to publish packages with different files for each target language.
3. Support for ValueOption module

[alfonsogarciacaro]

UPDATE: Commits concerning this and below comments have been moved to #3282

@dbrattli If you want to identify Fable.Core.U2 and friends, here's how to do it (using a regex). I haven't added yet logic for identifying all types of erased union, which would be more complex, so for now is probably to still output any or its equivalent in those cases.

[dbrattli]

@alfonsogarciacaro I just played with this example:

[<Erase>]
type ErasedUnion =
    | ErasedInt of int
    | ErasedString of string


let test () =
    let erased = ErasedInt 5
    ()

Which currently outputs:

def test(__unit: None=None) -> None:
    erased: ErasedUnion = 5

So I need to figure out where to translate ErasedUnion into int since the type ErasedUnion cannot be used. So is that the reason for the types not being translated correctly?

[alfonsogarciacaro]

Yes, but it's a bit complicated because erased unions can be compiled in different ways. I will update the documentation and add a helper tomorrow so it's clearer.

[dbrattli]

PS: I btw managed to get U2/U3/... working with Python:

let test (arg: U2<string, int>) =
    ()

test (U2.Case2 10)
let a : U3<string, int, float> = U3.Case1 "hello"

from typing import Union

def test(arg: Union[str, int]) -> None:
    pass


test(10)

a: Union[str, int, float] = "hello"

[alfonsogarciacaro]

Because I realized I still need to fix reflection for erased records and unions and also Rust tests, maybe this cannot make it into Fable 4 release, so I've moved the erased record/union part to #3282