Building on Guix

[roptat]

Hi :)

I'm trying to build opam2nix on Guix, using existing Guix packages (and importing dependencies that are not yet in the distribution). I tried to build v1.2.0 as well as the latest commit, and get the following error:

File "src/opam_metadata.ml", line 30, characters 28-44:
30 | 	| ExternalDependencies of (OpamSysPkg.Set.t * OpamTypes.filter) list
                                 ^^^^^^^^^^^^^^^^
Error: Unbound module OpamSysPkg
  version_ml src/version.ml

Am I missing a dependency? Am I using something that's too old/too recent?

[timbertson]

The opam libraries are defined in nix/opam.nix, but the source comes from wrangle.json - each of those libraries comes from the opam repo, which I've currently pinned to version 2.1.0-beta:

opam2nix/nix/wrangle.json

Lines 16 to 27 in f6b45ed

	"opam": {
	"fetch": {
	"owner": "ocaml",
	"repo": "opam",
	"rev": "11fcbc9e4bd7cca322f3020ed414531737012bd4",
	"sha256": "04042ayhpi76g0zp4fihsy1da7szmfhykii892wq2307r8y886wv"
	},
	"owner": "ocaml",
	"ref": "2.1.0-beta",
	"repo": "opam",
	"type": "github"
	},

Fair warning: I do have a rather invasive script to rip out some dependencies for opam-client: https://github.com/timbertson/opam2nix/blob/f6b45ed9e95e468f2971f7fee9dd5abbbc1d7577/nix/opam-client-minimal.sh
That's just to eliminate the need for dose, etc, but if you have those packaged already you should be fine to just use the full opam-client, at least to get started with. I should probably just vendor the functions I need from opam-client, but I worked hard to get them upstreamed in the first place 😆

[roptat]

ah, thanks! the package builds with opam 2.1.0-beta2. I was looking at the opam2nix.opam file, where there is no constraint. you might want to add one :). Now I managed to build it, but I'm not sure how to run it on the build side. I found this opam2nix invoke patch (build, install), but I get Missing environment variable: out. Is this supposed to be the output of the derivation? Also, how do I pass the name of the opam file I want to build the sources with?

[timbertson]

Yeah, the .opam file is not actually used (aside from some experiments I was trying), I should probably just delete it.

out is set by nix to the derivation's output / destination path, but it's only set when building a derivaiton. Are you running tis inside a derivation or just testing it out in a shell for now? I assume guix also sets $out during build, but maybe it uses something different. If you just want to try it outside a derivation, setting it to /tmp/whatever should get you a bit further.

Once you get past that, you'll also need to set opamEnv, which is a JSON serialization of all dependencies. That's set up here in the nix code:

opam2nix/nix/api.nix

Lines 116 to 124 in f6b45ed

	opamEnv = builtins.toJSON {
	inherit (args) version;
	name = args.pname;
	deps = mapAttrs (name: impl:
	if isPseudo impl then impl else {
	path = impl;
	inherit (impl) version;
	}
	) ({ inherit ocaml; } // args.opamInputs);

And it's loaded here in ocaml code, if that's useful:

opam2nix/src/invoke.ml

Lines 73 to 120 in f6b45ed

	let () = match json with
	| `Assoc pairs -> begin
	pairs |> List.iter (function
	| "deps", `Assoc (attrs) -> begin
	debug "adding packages from opamEnv\n";
	attrs |> List.iter (fun (pkgname, value) ->
	match value with
	| `Null -> add_package pkgname Absent
	(* Bool is used for base packages, which have no corresponding path *)
	| `Bool b -> add_package pkgname (if b then Provided else Absent)
	| `Assoc attrs -> (
	let path = ref None in
	let version = ref None in
	attrs |> List.iter (fun (key, value) ->
	match (key, value) with
	| "path", `String value -> path := Some value
	| "version", `String value -> version := Some (Version.of_string value)
	| "version", `Null -> version := None
	| _, other -> unexpected_json ("deps." ^ pkgname) other
	);
	add_package pkgname (Installed {
	(* path is optional in the type, but by `invoke` time all paths
	* should be defined *)
	path = Some (!path
	|> Option.or_failwith "missing `path` in deps"
	|> OpamFilename.Dir.of_string);
	version = !version;
	})
	)
	| other -> unexpected_json "deps value" other
	)
	end
	| "deps", other -> unexpected_json "deps" other
	| "name", `String name -> self_name := Some name;
	| "name", other -> unexpected_json "name" other
	| "version", `String version -> self_version := Some (Version.of_string version);
	| "version", other -> unexpected_json "version" other
	| other, _ -> failwith ("unexpected opamEnv key: " ^ other)
	)
	end
	| other -> unexpected_json "toplevel" other
	in

[timbertson]

(ugh tabs render so ugly in github UI...)