Fix dialyzer; only support custom fmt validator as root option

README.md

@@ -176,6 +176,8 @@ The custom function can also be an anonymous function:
 ExJsonSchema.Schema.resolve(%{"format" => "custom"}, custom_format_validator: fn format, data -> true end)
 ```
 
+> Note that the anonymous function version of the custom validator is only available in the option to Schema.resolve/2 and not as Application config, as using anonymous functions as configuration is not allowed.
+
 [format-spec]: https://json-schema.org/understanding-json-schema/reference/string.html#format
 
 ## License

lib/ex_json_schema/schema/root.ex

@@ -12,6 +12,6 @@ defmodule ExJsonSchema.Schema.Root do
           location: :root | String.t(),
           definitions: %{String.t() => ExJsonSchema.Schema.resolved()},
           version: non_neg_integer | nil,
-          custom_format_validator: {module(), atom()} | nil
+          custom_format_validator: {module(), atom()} | (String.t(), any() -> boolean | {:error, any()}) | nil
         }
 end

lib/ex_json_schema/validator/format.ex

@@ -99,7 +99,6 @@ defmodule ExJsonSchema.Validator.Format do
   defp do_validate(%Root{custom_format_validator: nil}, format, data) do
     case Application.fetch_env(:ex_json_schema, :custom_format_validator) do
       :error -> []
-      {:ok, validator} when is_function(validator, 2) -> validate_with_custom_validator(validator, format, data)
       {:ok, validator = {_mod, _fun}} -> validate_with_custom_validator(validator, format, data)
     end
   end