Remove devShell. Use devShells.default instead.

all-modules.nix

@@ -3,7 +3,6 @@
   imports = [
     ./modules/checks.nix
     ./modules/darwinModules.nix
-    ./modules/devShell.nix
     ./modules/devShells.nix
     ./modules/flake.nix
     ./modules/legacyPackages.nix

modules/devShell.nix

@@ -1,51 +0,0 @@
-{ config, lib, flake-modules-core-lib, ... }:
-let
-  inherit (lib)
-    filterAttrs
-    mapAttrs
-    mkOption
-    optionalAttrs
-    types
-    ;
-  inherit (flake-modules-core-lib)
-    mkSubmoduleOptions
-    ;
-in
-{
-  options = {
-    flake = mkSubmoduleOptions {
-      devShell = mkOption {
-        type = types.lazyAttrsOf types.package;
-        default = { };
-        description = ''
-          For each system a derivation that nix develop bases its environment on.
-        '';
-      };
-    };
-  };
-  config = {
-    flake.devShell = mapAttrs (k: v: v.devShell) config.allSystems;
-
-    perInput = system: flake:
-      optionalAttrs (flake?devShell.${system}) {
-        devShell = flake.devShell.${system};
-      };
-
-    perSystem = system: { config, ... }: {
-      _file = ./devShell.nix;
-      options = {
-        devShell = mkOption {
-          type = types.package;
-          # We don't have a way to unset devShell in the flake without computing
-          # the root of each allSystems module, so to improve laziness, the best
-          # choice seems to be to require a devShell and give the opportunity
-          # to unset it manually.
-          default = throw "The default devShell was not configured for system ${system}. Please set it, or if you don't want to use the devShell attribute, set flake.devShell = lib.mkForce {};";
-          description = ''
-            A derivation that nix develop bases its environment on.
-          '';
-        };
-      };
-    };
-  };
-}