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init: devshell for hands-on onboarding #119966

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init: devshell for hands-on onboarding #119966

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5044f8d
init: devshell for hands-on onboarding
Apr 20, 2021
b9bd449
devhsell: pin nixpkgs version
Apr 21, 2021
4c24484
devshell: use good old nix
Apr 21, 2021
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5 changes: 5 additions & 0 deletions flake.nix
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Expand Up @@ -63,6 +63,11 @@
});

checks.x86_64-linux.tarball = jobs.tarball;
devShell = {
x86_64-linux = import ./shell.nix { system = "x86_64-linux"; };
x86_64-darwin = import ./shell.nix { system = "x86_64-darwin"; };
aarch64-linux = import ./shell.nix { system = "aarch64-linux"; };
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Do we really have to manually list every platform here? What happens to somebody who isn't on one of those three platforms? (aarch64-darwin and powerpc64le-linux come to mind.)

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@blaggacao blaggacao Apr 22, 2021 •
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When writing I had a bad stomach feeling, already. 😉

numtide/flake-utils has a defaultSystem. Do we have something similar to enumerate on the "blessed" set of systems as flake spec requires?

Maybe we also could just add those two to suport 'most common' platforms? What do you think?

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Somebody on a different platfrom currenrly still can try nix-shell directly using shell.nix circumventing flake.nix.

};

htmlDocs = {
nixpkgsManual = jobs.manual;
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45 changes: 45 additions & 0 deletions shell.nix
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@@ -0,0 +1,45 @@
{ system ? builtins.currentSystem }:
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Is this file supposed to only use builtins?

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Yes, it shall have no other dependency.

I'd rather avoid public interfaces, where we can. Everything needed will be conveniently contained within devshell and nixpkgs.

let
# nixpkgs / devshell is only used for development. Don't add it to the flake.lock.
nixpkgsGitRev = "5268ee2ebacbc73875be42d71e60c2b5c1b5a1c7";
devshellGitRev = "709fe4d04a9101c9d224ad83f73416dce71baf21";

nixpkgsSrc = fetchTarball {
url = "https://github.com/NixOS/nixpkgs/archive/${nixpkgsGitRev}.tar.gz";
sha256 = "080fvmg0i6z01h6adddfrjp1bbbjhhqk32ks6ch9gv689645ccfq";
};


devshellSrc = fetchTarball {
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Flakes shouldn't use `builtins.{fetchTarball,fetchGit,...}. This may even become impossible in the future. Dependencies should be expressed at the flake level so they can be queried and updated in a uniform way.

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@blaggacao blaggacao Apr 21, 2021 •
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Thanks for pointing this out! We had a large discussion over at divnix/devos if this is an antipattern or actually a good pattern. Most lock files, support some notion of development dependencies and "usage" dependency (for not to say "runtime").

For example flake-utils-plus like numtide/flake-utils has a policy to depend on nothing, but builtins. This makes a lot of sense so that no subtle incompatibilities would be introduced since coded against one nixpkgs version it could be instantiated with another.

Importing those dependencies via flake inputs, for those packages it would be absolutely out of question to provide such development amentities. Until flakes support dev-only (optional) dependencies, which are not required for using a flake, this is the only pattern we could find to map this use case concisely into code.

Would you be ok to remain explicit in a sense that once flake supports that, we can change it, or would you still prefer to bury that subtle distinction and make it explicit once flake's support it? I don't have any vested preferences here.

url = "https://github.com/numtide/devshell/archive/${devshellGitRev}.tar.gz";
sha256 = "1px9cqfshfqs1b7ypyxch3s3ymr4xgycy1krrcg7b97rmmszvsqr";
};

pkgs = import nixpkgsSrc { inherit system; };
devshell = import devshellSrc { inherit system pkgs; };
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I see a fundamental problem here: There is no way to introduce breaking changes in nixpkgs that touch devshell without patching the latter along. Otherwise the shell will simply break. We just added quite an arbitrary dependency.

Technically correct solution would be to pass the historic version of nixpkgs that devshell was developed against, but that's quite expensive.

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Technically correct solution would be to pass the historic version of nixpkgs that devshell was developed against, but that's quite expensive.

I can see the problem. For the reasonable future, I think devshell will be well maintained and any breakage will be resolved within days, not weeks.

The problem manifests once/if (core) maintainers or the CI becomes heavily dependent on it. By then, devshell, whose stated objective is to completment mkShell here in nixpkgs, will either be already upstreamed or heavily maintained.

Historical nixpkgs, without further guardrails, would imply historical nixpkgs-fmt, historical nixpkgs-review, etc, etc.

I think cost benefit tips slightly towards accepting the risk that it (might evnetually maybe) break. ... and fix it when we get there.


in
devshell.mkShell {
devshell = {
name = "nixpkgs";
packages = with pkgs; [
fd
nixpkgs-fmt
];
};

commands = [
{
name = "fmt";
help = "Check Nix formatting";
category = "linters";
command = "nixpkgs-fmt $${@} .";
}
{
name = "evalnix";
help = "Check Nix parsing";
category = "linters";
command = "fd --extension nix --exec nix-instantiate --parse --quiet {} >/dev/null";
}
];
}