refactor(build): onix based env

Makefile

@@ -18,3 +18,8 @@ opam-install-deps:
 
 format:
 	dune build @fmt --auto-promote
+
+onix-lock:
+	onix lock ./gcloud.opam ./gcloud-cli.opam --resolutions="ocaml-system=5.2.0" --lock-file ./onix-lock.json
+	onix lock ./gcloud.opam ./gcloud-cli.opam ./gcloud-melange.opam --resolutions="ocaml-system=5.2.0" --with-dev-setup=true --with-test=true --lock-file ./onix-lock-dev.json
+	git add onix-lock.json onix-lock-dev.json

README.md

@@ -1,2 +1,21 @@
 OCaml bindings to the Google Cloud Platform APIs
 ================================================
+
+## Development
+
+The default nix devShell will have the packages needed to develop `ocaml-gcloud`:
+```
+nix develop '.#' # (or use nix-direnv)
+dune build ...
+```
+
+### Updating opam package set
+
+If you've updated the `.opam` files in the project and need to recalculate the `opam` deps, run `make onix-lock` and refresh the devShell:
+
+```
+# From inside the nix devShell
+$ make onix-lock
+$ exit # (or nix-direnv-reload if using nix-direnv)
+$ nix develop '.#'
+```

flake.nix

@@ -3,100 +3,38 @@
     nixpkgs.url = "nixpkgs/nixpkgs-unstable";
     flake-utils.url = "github:numtide/flake-utils";
 
-    opam-nix = {
-      url = "github:tweag/opam-nix";
-      inputs.opam-repository.follows = "opam-repository";
-    };
-    opam-repository = {
-      url = "github:ocaml/opam-repository";
-      flake = false;
-    };
+    onix.url = "github:rizo/onix";
+    onix.inputs.nixpkgs.follows = "nixpkgs";
   };
 
-  outputs = { self, nixpkgs, flake-utils, opam-nix, opam-repository }@inputs:
+  outputs = { self, nixpkgs, flake-utils, onix }@inputs:
     flake-utils.lib.eachDefaultSystem (system:
       let
         pkgs = nixpkgs.legacyPackages.${system};
-        fs = pkgs.lib.fileset;
-        on = opam-nix.lib.${system};
-        ocaml-version = "5.1.1";
-        ocaml-base-compiler = ocaml-version;
-
-        # List of opam files you which to be read by opam-nix
-        opamFiles = [
-          ./gcloud.opam
-          ./gcloud-cli.opam
-
-          # Also include the opam files to any submoduled dependencies
-          # ./vendor/some-lib/some-lib.opam
-        ];
-
-        opamFilePackageNames = (map (x:
-          (pkgs.lib.removeSuffix ".opam" (builtins.baseNameOf (toString x))))
-          opamFiles);
-
-        # attrset containing all opam packages defined in the opamFiles list
-        # for a specific OCaml version
-        opamScope = (on.buildOpamProject' {
-          repos = [ opam-repository ];
-          resolveArgs.with-test = true;
-          recursive = true;
-          overlays = on.__overlays ++ [
-            (final: prev:
-              builtins.foldl' (acc: pkg:
-                (acc // {
-                  # Allows us to treat the whole repo as a single unit and `dune build` it together,
-                  # without opam-nix attempting to build each opam package individually.
-                  # Similar to opam install --deps-only
-                  ${pkg} =
-                    prev.${pkg}.overrideAttrs (oa: { dontBuild = true; });
-                })) {
-                  # other-package-override = prev.other-package-overide.overrideAttrs (oa: {
-                  #   nativeBuildInputs = oa.nativeBuildInputs ++ (with pkgs; [ makeWrapper git ]);
-                  # });
-                } opamFilePackageNames)
-          ];
-        } (fs.toSource {
-          root = ./.;
-          fileset = fs.unions opamFiles;
-        }) { inherit ocaml-base-compiler; });
-
-        gcloud-cli = pkgs.stdenv.mkDerivation {
-          pname = "gcloud-cli";
-          version = "1.0.0";
-          buildInputs = (map (p: opamScope.${p}) opamFilePackageNames);
-          buildPhase = ''
-            dune build @install -p gcloud,gcloud-cli
-          '';
-
-          installPhase = ''
-            mkdir -p $out/bin
-            cp _build/install/default/bin/* $out/bin/
-          '';
-
-          src = (fs.toSource {
-            root = ./.;
-
-            # Prevent changes to the nix flake file from busting the build cache.
-            # Add any other files which the build should ignore to this list.
-            fileset =
-              fs.difference ./. (fs.unions [ ./flake.nix ./flake.lock ]);
-          });
+        onix' = onix.packages.${system}.latest;
+        onixEnv = onix'.env {
+          path = ./.;
+          # roots = [./gcloud.opam ./gcloud-cli.opam];
+          lock = ./onix-lock.json;
+        };
+        onixEnvDev = onix'.env {
+          path = ./.;
+          # roots = [./gcloud.opam ./gcloud-cli.opam];
+          lock = ./onix-lock-dev.json;
         };
 
       in rec {
         # for use by nix fmt
         formatter = pkgs.nixfmt-rfc-style;
 
-        packages.gcloud-cli = gcloud-cli;
+        packages.gcloud-cli = onixEnv.pkgs.gcloud-cli;
 
-        packages.default = pkgs.mkShell {
-          dontDetectOcamlConflicts = true;
-          buildInputs = (map (p: opamScope.${p}) opamFilePackageNames) ++ [
-            pkgs.ocaml-ng.ocamlPackages_5_1.utop
-            pkgs.ocaml-ng.ocamlPackages_5_1.ocaml-lsp
-            pkgs.ocamlformat_0_22_4
-          ];
-        };
+        devShells.onixLock = pkgs.mkShell { buildInputs = [ onix' ]; };
+
+        devShells.default = onixEnvDev.shell.overrideAttrs (final: prev: {
+          buildInputs = prev.buildInputs ++ [ pkgs.ocamlformat_0_22_4 onix' ];
+        });
+
+        packages.dev-shell = devShells.default.inputDerivation;
       });
 }