Only consume body when http code doesn't cause immediate rejection

[WalternativE]

• To give consuming clients the chance to parse the body themselves for
  non-success status codes. This is especially important to extract
  additional information about errors encoded in the response bodies.

[MangelMaxime]

Hello @WalternativE,

I am not sure about these changes because if you have an error it will still be captured by |> Promise.catch (NetworkError >> Error) when using tryFetchAs. And so result in an Error (NetworkError (Error FetchFailed)).

Can you please add tests to see what you want to achieve?

[WalternativE]

I added a test for the scenario I had in mind. Maybe this makes the situation clearer. My problem is that currently the resolve function always reads the text of the fetch response. If the status code is a non-success it packs the response in an Error(FetchFailed response). I can get this response and try to parse the information I need but unfortunately I cannot re-read the body. All the information (and it's not unconventional to return very specific error information in many APIs) in the body is lost to me. That's why I proposed the changes you see in this PR.

Might very well be that there is a way to re-read the body which I didn't consider. Did I overlook something?

[MangelMaxime]

Ok, I see.

I had well understood your case but I didn't know we couldn't read several times the body. So here, you are delaying it until last time.

I also originally misunderstood what Promise.lift does.

Because your test is passing and all the others are still green I will release a new beta version.

[MangelMaxime]

Thoth.Fetch 2.0.0-beta-002 has been released.

[WalternativE]

Thanks, Maxime. Also: thank you very much for all your work. I haven't been doing a lot of Fable work in the last couple of months, so the current developer experience really blew me away. ❤

[MangelMaxime]

Thank you for telling me and really happy that you like the developer experience :)