Enable the use of a `shell.nix` file as environment definition.

[Equanox]

It's currently not possible to load an development environments from a shell.nix file which makes use of the pkgs.mkShell utility function due to the way Bob builds nix package and creates the environment for it's internal shell.

How Bob calls nix-build && nix-shell

Bob uses nix-build to build nix package and the output of nix-shell to create a fully controlled build environement. Inbetween those calls Bob uses caching to assure that no extra work is done. The intend was to make it easier to depend on nix packages without the need to understand the nix language.

Bob calls to nix-*

1) nix-build:

nix-build --no-out-link -E with import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/refs/tags/23.05.tar.gz") { }; [go_1_20]

2) nix-shell:

nix-shell --pure --keep NIX_SSL_CERT_FILE --command env -E 
{ pkgs ? import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/refs/tags/23.05.tar.gz") {} }:
pkgs.mkShell {
  buildInputs = [
    pkgs.go_1_20
   (pkgs.callPackage ./oapicodegen_v1.12.4.nix{ } )
   (pkgs.callPackage ./empty.nix{ } )
 ];
}

Content of empty.nix

{ pkgs ? import <nixpkgs> {} }:

pkgs.mkShell {
  buildInputs = [];
}

Content of oapicodegen_v1.12.4.nix

{ lib, buildGoModule }:

buildGoModule rec {
  # Args...
}

The call to nix-shell fails with an error

exit status 127
/nix/store/zb4vimfhcgc8hphkqmmfcj2lxmgg9y2f-nix-shell: line 1: ------------------------------------------------------------: command not found
/nix/store/37p8gq9zijbw6pj3lpi1ckqiv18j2g62-stdenv-linux/setup: line 703: pop_var_context: head of shell_variables not a function context
/nix/store/37p8gq9zijbw6pj3lpi1ckqiv18j2g62-stdenv-linux/setup: line 710: pop_var_context: head of shell_variables not a function context

Possible Solution

A solution could be to to introduce a new shell: directive which takes the path to a shell.nix file like you would do it with plain nix-shell. Internally it would omit the nix-build -> cache -> nix-shell chain. The shell: and dependencies: directive are mutually exclusive.

cc: @srstrong

[Equanox]

#366

@srstrong please check https://github.com/benchkram/bob/releases/tag/0.8.2-nix-shell-2

To download the version directly use:
curl -L https://bob.build/install.sh | BIN_DIR=bin BOB_VERSION=0.8.2-nix-shell-2 sh

[dlouwers]

As you have noticed from previous conversations I am working to make bob play nice with DevContainers.

The change is working pretty well for me so far. I can instruct IDE's to use nix-shell as their default shell. I will have to test several plugins to see if they can reach the tooling since configurations vary from plugin to plugin. Baseline works well with VSCode:

"settings": {
  "terminal.integrated.profiles.linux": {
    "nix-shell": {
      "path": "/nix/var/nix/profiles/default/bin/nix-shell", 
        "args": [
          "backoffice/shell.nix"
         ]
     }
   },
   "terminal.integrated.defaultProfile.linux": "nix-shell"
}  

Will try it with the rust-analyzer plugin first since that seems to require quite a lot of tooling in its environment.

[dlouwers]

Even though this is an improvement, after investigation it seems to be incredibly hard to setup a devcontainer in a way that, for instance, VSCode plugins can find the tooling needed. For example I have been unable to create a devcontainer that exposes the needed language server for rust when I have a dependency on rustup. Yes, the VSCode shell has it available but the rust language plugin for VSCode does not use that environment. I have tried everything I could think of to be able to have the plugin run the tooling in the context of the nix shell or even make nix dependencies available system wide but failed so far. Please let me know if anyone else has had better luck.