mx-sanebot: split shell and default out of flake.nix

pkgs/mx-sanebot/default.nix

@@ -0,0 +1,19 @@
+{ lib
+, cargo-docset ? null
+, openssl
+, pkg-config
+, rustPlatform
+}:
+
+# docs: <nixpkgs>/doc/languages-frameworks/rust.section.md
+rustPlatform.buildRustPackage {
+  name = "mx-sanebot";
+  src = ./.;
+  cargoLock.lockFile = ./Cargo.lock;
+
+  nativeBuildInputs = [ pkg-config ] ++ lib.optional (cargo-docset != null) cargo-docset;
+  buildInputs = [ openssl ];
+
+  # enables debug builds, if we want: https://github.com/NixOS/nixpkgs/issues/60919.
+  hardeningDisable = [ "fortify" ];
+}

pkgs/mx-sanebot/flake.nix

@@ -11,35 +11,10 @@
       pkgs = import nixpkgs {
         inherit system;
       };
-      nativeBuildInputs = with pkgs; [
-        pkg-config
-      ];
-      buildInputs = with pkgs; [
-        openssl
-      ];
     in rec {
-      packages = {
-        # docs: <nixpkgs>/doc/languages-frameworks/rust.section.md
-        mx-sanebot = pkgs.rustPlatform.buildRustPackage {
-          name = "mx-sanebot";
-          src = ./.;
-          cargoLock.lockFile = ./Cargo.lock;
-          # enables debug builds, if we want: https://github.com/NixOS/nixpkgs/issues/60919.
-          hardeningDisable = [ "fortify" ];
-          inherit buildInputs nativeBuildInputs;
-        };
-      };
+      packages.mx-sanebot = pkgs.callPackage ./default.nix { };
       defaultPackage = packages.mx-sanebot;
 
-      devShells.default = with pkgs; mkShell {
-        # enables debug builds, if we want: https://github.com/NixOS/nixpkgs/issues/60919.
-        hardeningDisable = [ "fortify" ];
-
-        # Allow cargo to download crates.
-        SSL_CERT_FILE = "${cacert}/etc/ssl/certs/ca-bundle.crt";
-
-        inherit buildInputs;
-        nativeBuildInputs = [ cargo ] ++ nativeBuildInputs;
-      };
+      devShells.default = ./shell.nix { inherit pkgs; };
     });
 }

pkgs/mx-sanebot/shell.nix

@@ -0,0 +1,13 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+let
+  mx-sanebot = pkgs.callPackage ./. { };
+in
+  pkgs.mkShell {
+    nativeBuildInputs = mx-sanebot.buildInputs ++ mx-sanebot.nativeBuildInputs ++ [
+      pkgs.cargo
+    ];
+
+    # Allow cargo to download crates.
+    SSL_CERT_FILE = "${cacert}/etc/ssl/certs/ca-bundle.crt";
+  }