diff options
| -rw-r--r-- | lib/types.nix | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/lib/types.nix b/lib/types.nix index f47a1f92de7..c35f055e17f 100644 --- a/lib/types.nix +++ b/lib/types.nix @@ -581,7 +581,17 @@ rec { in mkOptionType rec { name = "enum"; - description = "one of ${concatMapStringsSep ", " show values}"; + description = + # Length 0 or 1 enums may occur in a design pattern with type merging + # where an "interface" module declares an empty enum and other modules + # provide implementations, each extending the enum with their own + # identifier. + if values == [] then + "impossible (empty enum)" + else if builtins.length values == 1 then + "value ${show (builtins.head values)} (singular enum)" + else + "one of ${concatMapStringsSep ", " show values}"; check = flip elem values; merge = mergeEqualOption; functor = (defaultFunctor name) // { payload = values; binOp = a: b: unique (a ++ b); }; |