I like the idea of passing specialArgs to nixosConfigurations when using flakes.
Is this supposed to work with devShells too ?
Asking bc I suppose devenv let’s me use:
inputs.devenv.lib.mkShell {
inherit inputs pkgs;
modules = [
({ unstable, ... }: {}
)]
};
had I specialArgs = forEachSystem (system: { inherit system; unstable = inputs.unstable.legacyPackages.${system}; }); defined.
Now my question would be is that possible using mkShell {} too ?
Where would the module parameter unstable in
let
inherit system specialArgs;
in pkgs.mkShell {}
go ?
No, that’s specifical to lib.evalModules:
and mkShell is just a derivation (special case of stdenv.mkDerivation) which doesn’t use the module system.
It wouldn’t, derivations are not modules.
I’m unclear what you intend to accomplish, I don’t use devenv.
But if you want the module system in flakes, I’ve only used flake-parts before.
(I never considered devenv as they require impurity by design.)
2 Likes
I’ll post a rough sketch of a minimal flake here ASAP to illustrate.
Not working (as @waffle8946 pointed out) example (nix develop .#devShells.x86_64-linux."devenv specialArgs" --impure):
{
description = "A very basic flake";
inputs = {
nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
unstable.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
devenv = {
url = "github:cachix/devenv";
inputs.nixpkgs.follows = "unstable";
};
};
outputs = { self, nixpkgs, ... }@inputs:
let
forEachSystem = nixpkgs.lib.genAttrs [ "x86_64-linux" ];
inherit (nixpkgs.lib) listToAttrs;
specialArgs = forEachSystem (system: {
inherit system;
unstable = inputs.unstable.legacyPackages.${system};
});
in {
devShells = forEachSystem (system: listToAttrs [
(
let
pkgs = inputs.nixpkgs.legacyPackages.${system};
in
{
name = "devenv specialArgs";
value = inputs.devenv.lib.mkShell {
inherit inputs pkgs;
modules = [
({ specialArgs, unstable, ... }: {
packages = builtins.attrValues {
inherit (specialArgs.unstable) eza;
};
enterShell = ''
eza --version
'';
})
];
};
}
)
]);
};
}
What’s of interest for me would be reusing this unstable attribute as analogous in specialArgs all over some dev shells I might have. Don’t know what idiom to use exactly for that.
flake-parts was pointed out, do you have an example how to utilize ?
To provide at least a working example of what I want functionally and answering half of my question here is:
{
description = "A very basic flake";
inputs = {
nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-24.05";
unstable.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
devenv = {
url = "github:cachix/devenv";
inputs.nixpkgs.follows = "unstable";
};
};
outputs = { self, nixpkgs, ... }@inputs:
let
forEachSystem = nixpkgs.lib.genAttrs [ "x86_64-linux" ];
inherit (nixpkgs.lib) listToAttrs;
specialArgs = forEachSystem (system: {
inherit system;
unstable = inputs.unstable.legacyPackages.${system};
});
in {
devShells = forEachSystem (system: listToAttrs [
(
let
pkgs = inputs.nixpkgs.legacyPackages.${system};
inherit specialArgs;
in
{
name = "devenv specialArgs";
value = inputs.devenv.lib.mkShell {
inherit inputs pkgs;
modules = [
({ ... }: {
packages = builtins.attrValues {
inherit (specialArgs.${system}.unstable.pkgs) eza;
};
enterShell = ''
eza --version
'';
})
];
};
}
)
]);
};
}
Second half question remains, what would a more nix-like solution look like ?
I’m not sure why you’d need specialArgs here, you already have unstable in scope, so something like this should work:
{
description = "A very basic flake";
inputs = {
nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-24.05";
unstable.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
devenv = {
url = "github:cachix/devenv";
inputs.nixpkgs.follows = "unstable";
};
};
outputs = { self, nixpkgs, ... }@inputs:
let
forEachSystem = nixpkgs.lib.genAttrs [ "x86_64-linux" ];
inherit (nixpkgs.lib) listToAttrs;
in {
devShells = forEachSystem (system: listToAttrs [
(
let
pkgs = inputs.nixpkgs.legacyPackages.${system};
# we make unstable just another let-binding
unstable = inputs.unstable.legacyPackages.${system};
in
{
name = "devenv specialArgs";
value = inputs.devenv.lib.mkShell {
inherit inputs pkgs;
modules = [
({ ... }: {
packages = builtins.attrValues {
inherit (unstable.pkgs) eza; # use unstable from the outer scope
};
enterShell = ''
eza --version
'';
})
];
};
}
)
]);
};
}