# https://github.com/NixOS/nixpkgs/blob/a5cfe012401cfebb4b2c28e74857b8ffe1402b4b/lib/modules.nix
{ lib }:
with lib.modules;
let
  inherit (lib)
    addErrorContext
    all
    any
    attrByPath
    attrNames
    catAttrs
    concatLists
    concatMap
    concatStringsSep
    elem
    filter
    foldl'
    functionArgs
    getAttrFromPath
    genericClosure
    head
    id
    imap1
    isAttrs
    isBool
    isFunction
    isInOldestRelease
    isList
    isString
    length
    mapAttrs
    mapAttrsToList
    mapAttrsRecursiveCond
    min
    optional
    optionalAttrs
    optionalString
    recursiveUpdate
    reverseList sort
    seq
    setAttrByPath
    substring
    throwIfNot
    trace
    typeOf
    types
    unsafeGetAttrPos
    warn
    warnIf
    zipAttrs
    zipAttrsWith
    ;
  inherit (lib.options)
    isOption
    mkOption
    showDefs
    showFiles
    showOption
    unknownModule
    ;
  inherit (lib.strings)
    isConvertibleWithToString
    ;

  unifyModuleSyntax = file: key: m:
    let
      addMeta = config: if m ? meta
        then mkMerge [ config { meta = m.meta; } ]
        else config;
      addFreeformType = config: if m ? freeformType
        then mkMerge [ config { _module.freeformType = m.freeformType; } ]
        else config;
    in
    if m ? config || m ? options then
      let badAttrs = removeAttrs m ["_class" "_file" "key" "disabledModules" "imports" "options" "config" "meta" "freeformType"]; in
      if badAttrs != {} then
        throw "Module `${key}' has an unsupported attribute `${head (attrNames badAttrs)}'. This is caused by introducing a top-level `config' or `options' attribute. Add configuration attributes immediately on the top level instead, or move all of them (namely: ${toString (attrNames badAttrs)}) into the explicit `config' attribute."
      else
        { _file = toString m._file or file;
          _class = m._class or null;
          key = toString m.key or key;
          disabledModules = m.disabledModules or [];
          imports = m.imports or [];
          options = m.options or {};
          config = addFreeformType (addMeta (m.config or {}));
        }
    else
      # shorthand syntax
      throwIfNot (isAttrs m) "module ${file} (${key}) does not look like a module."
      { _file = toString m._file or file;
        _class = m._class or null;
        key = toString m.key or key;
        disabledModules = m.disabledModules or [];
        imports = m.require or [] ++ m.imports or [];
        options = {};
        config = addFreeformType (removeAttrs m ["_class" "_file" "key" "disabledModules" "require" "imports" "freeformType"]);
      };


in {inherit unifyModuleSyntax;}