Port nix.sh to the fish shell

[tchajed]

Sourcing nix.sh won't work on fish shell since it doesn't use the same syntax. This patch adds a new nix.fish that can be sourced from fish.

[domenkozar]

I've seen requests for this, it's going to be pain to maintain (we'd need a test).

[Ericson2314]

@domenkozar Hmm? I think it would be pretty popular and thus less likely to rot. But what tests were you thinking of?

[domenkozar]

@tchajed could you rebase and sync with recent changes? I don't see why we shouldn't support this as long as it's maintained.

[yacinehmito]

@tchajed What is the status on this please ? I would be happy to help.

[tchajed]

It looks like the sh profile has become more complicated. While I fixed merge conflicts, the new profile needs to be translated to fish again. I'm not able to get nix to compile, and since I don't actually use it I'd rather pass this on to someone who will maintain it.

@gpyh: feel free to use this as a starting point and create your own pull request! I'd rather not submit code I haven't tested.

[nhooyr]

I'm gonna try and work on this in a new PR.

[pickfire]

Any news on this?

[tchajed]

I'm closing in favor of the latest attempt by @asymmetric in #1090, which hopefully gets resolved and merged.

[pickfire]

@tchajed @asymmetric issue was closed.