refactor(shell): use create-simple-derivations helper

snowfall-lib/shell/default.nix

@@ -4,20 +4,9 @@
   snowfall-lib,
   snowfall-config,
 }:
-let
-  inherit (core-inputs.flake-utils-plus.lib) filterPackages;
-  inherit (core-inputs.nixpkgs.lib)
-    assertMsg
-    foldl
-    mapAttrs
-    callPackageWith
-    ;
-
-  user-shells-root = snowfall-lib.fs.get-snowfall-file "shells";
-in
 {
   shell = {
-    ## Create flake output packages.
+    ## Create flake output shells.
     ## Example Usage:
     ## ```nix
     ## create-shells { inherit channels; src = ./my-shells; overrides = { inherit another-shell; }; alias = { default = "another-shell"; }; }
@@ -27,41 +16,7 @@ in
     ## { another-shell = ...; my-shell = ...; default = ...; }
     ## ```
     #@ Attrs -> Attrs
-    create-shells =
-      {
-        channels,
-        src ? user-shells-root,
-        pkgs ? channels.nixpkgs,
-        overrides ? { },
-        alias ? { },
-      }:
-      let
-        user-shells = snowfall-lib.fs.get-default-nix-files-recursive src;
-        create-shell-metadata =
-          shell:
-          let
-            extra-inputs = pkgs // {
-              inherit channels;
-              lib = snowfall-lib.internal.system-lib;
-              inputs = snowfall-lib.flake.without-src user-inputs;
-              namespace = snowfall-config.namespace;
-            };
-          in
-          {
-            # We are building flake outputs based on file paths. Nix doesn't allow this
-            # so we have to explicitly discard the string's path context to use it as an attribute name.
-            name = builtins.unsafeDiscardStringContext (snowfall-lib.path.get-parent-directory shell);
-            drv = callPackageWith extra-inputs shell { };
-          };
-        shells-metadata = builtins.map create-shell-metadata user-shells;
-        merge-shells =
-          shells: metadata:
-          shells
-          // {
-            ${metadata.name} = metadata.drv;
-          };
-        shells = snowfall-lib.attrs.merge-with-aliases merge-shells shells-metadata alias // overrides;
-      in
-      filterPackages pkgs.stdenv.hostPlatform.system shells;
+    create-shells = args:
+      snowfall-lib.internal.create-simple-derivations (args // { type = "shells"; });
   };
 }