Merge pull request #9 from hacklanta/empty-validation

Empty Validation: Allow validating fields that are not sent to the server

We have an issue where an empty field can't be marked as invalid because
it never gets a chance to run against validations. To fix this, we:

 - Separate the computation of the final, fully validated value of the field
   into its own method, and cache it in a `TransientRequestVar`.
 - Cache the field name in a `RequestVar` and abstract out the adding of
   a validation error for the field based on this cache.
 - Introduce a new concept, boxed validations, which are validations that
   can take boxes of the field value instead of just the field value.
 - Add overloads for `withValidation` and `?` to be able to add boxed
   validations.
 - Run those validators when computing the final value if there is no seen
   value for the field, allowing the boxed validators to run even if there is
   no submission for the field.

.gitignore

@@ -2,6 +2,7 @@
 .DS_Store
 .DS_Store?
 .ensime
+.ensime_cache/
 .ensime_lucene/
 .history
 .idea_modules/

README.md

@@ -48,7 +48,7 @@ A basic form snippet would look like this:
       // Assuming a case class User(name: String, age: Int, phoneNumber: String, termsAndConditions: Boolean).
       User(name, age, phoneNumber, termsAndConditions).save
     }
-  
+
   "form" #> registrationForm.binder
 ```
 
@@ -142,6 +142,15 @@ the set of validations that are supported by
 [Parsley.js](http://parsleyjs.org). These will have matching server-side
 validation implementations.
 
+In certain very specific cases, it can be useful to run a validation even
+if the value in question isn't actually submitted in the form. Typically
+this is used for a check that a required field was submitted, particularly
+when it comes from a checkbox or radio button. Either way, in these cases
+a validation can take a `Box[T]` instead of `T`. It will receive an `Empty`
+if the field is not submitted, and a `Full` with the deserialized value if
+the field is submitted. Lift-formality's own `notBlank`/`notEmpty` validators
+will correctly handle unsubmitted fields.
+
 ### Event handling
 
 Formality can also add server-side event handlers to form inputs: