lib/types: Allow types to emit a deprecation warning

Previously the only way to deprecate a type was using

  theType = lib.warn "deprecated" (mkOptionType ...)

This caused the warning to be emitted when the type was evaluated, but
the error didn't include which option actually used that type.

With this commit, types can specify a deprecationMessage, which when
non-null, is printed along with the option that uses the type

1 files changed, 4 insertions, 1 deletions

diff --git a/lib/types.nix b/lib/types.nix
index 17e7a939fe3d..f999805e1a98 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -91,9 +91,12 @@ rec {
       #            combinable with the binOp binary operation.
       #   binOp: binary operation that merge two payloads of the same type.
       functor ? defaultFunctor name
+    , # The deprecation message to display when this type is used by an option
+      # If null, the type isn't deprecated
+      deprecationMessage ? null
     }:
     { _type = "option-type";
-      inherit name check merge emptyValue getSubOptions getSubModules substSubModules typeMerge functor;
+      inherit name check merge emptyValue getSubOptions getSubModules substSubModules typeMerge functor deprecationMessage;
       description = if description == null then name else description;
     };