fishPlugins: create scope and add some plugins

[pacien]

Motivation for this change

This bootstraps the fishPlugins scope and build tools for packaging plugins for the fish shell.

Two plugin packages are added:

• fishtape: a TAP-based test runner for Fish, often used to test fish plugins,
• pure: a pretty, minimal and fast Fish prompt, ported from zsh

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Poking people

CC'ing the most recent committers on the fish module and package as they might be interested in this PR:

• @cole-h
• @gebner
• @adisbladis
• @bouk
• @xaverdh
• @rnhmjoj
• @hyperfekt

[rnhmjoj]

It would be good to add documentation on how to add/use these plugins.
I can't figure how to use them: either with adding fishPlugins.something to environment.systemPackages or a nix-shell fish doesn't seems to find them, even with programs.fish.vendor.config.enable = true.

[pacien]

That's strange. This should be enough for the plugin to be detected by fish.

I'm using fish enabled through home-manager's programs.fish.enable and adding the packages to home.packages is enough for them to be detected.

[rnhmjoj]

I'm using fish enabled through home-manager's programs.fish.enable and adding the packages to home.packages is enough for them to be detected.

Uhm, I don't use home-manager, so I tried:

nix-shell -I nixpkgs=/path/to/nixpkgs --pure -p fish fishPlugins.fish-foreign-env -- run fish

but fenv is not available. Similarly, when I try a NixOS VM with:

nix-build -E '(import ./nixos { 
  configuration = { pkgs,... }: { 
    users.users.root.password = "root";
    programs.fish.enable = true;
    environment.systemPackages = with pkgs; [ fishPlugins.pure fishPlugins.fish-foreign-env ];
  }; }).vm'

[pacien]

It seems like the fish-foreign-env package was installing the scripts outside of the standard vendor_functions.d directory.
I modified the package (now fishPlugins.foreign-env) and the module accordingly and everything is correctly loaded now.

This is however a breaking change. Should I remove the package alias?

[rnhmjoj]

This is however a breaking change. Should I remove the package alias?

Uhm, it's likely it was never used outside of the NixOS module.
I'd say to add a note in the release notes but keep the alias.

[pacien]

Note added to the release notes and amended.

[rnhmjoj]

Thank you. I tested the NixOS module and built the manual: looks all good.

[rnhmjoj]

I don't have any other suggestions to make, the changes look good to me.
I'd wait for more fish users/maintainers to comment before merging, though.

[cole-h]

One small suggestion below, otherwise LGTM. Thanks for this, @pacien! And thanks @rnhmjoj for all your feedback / review.

[cole-h]

Diff LGTM. Thanks!

[pacien]

(Rebased to fix merrge conflict.)

[abathur]

@pacien I'm not a fish user so I don't have much insight, but it sounds like this breaking change is sneaking up on some nix-darwin users (LnL7/nix-darwin#269). I would guess it's doing the same for HM users?

[rnhmjoj]

Yeah, nix-darwin and probably home-manager need to change the foreign-env path as in this diff:
pacien@d94921d#diff-e643907e997ff11fbccddd7dacf176032a320f26f8313eb4b18f435597dca2b0

edit: Yeah, they're already onto it: nix-community/home-manager#1703

[pacien]

Should we remove the alias fish-foreign-env -> fishPlugins.foreign-env so that the evaluation fails instead of having runtime breakage? Those packages aren't compatible due to the directory layout changes, so I'm not sure that it made sense to have that alias in the first place.

[cole-h]

Yeah, I agree with that.