work around some validation exceptions

CHANGES.txt

@@ -13,6 +13,7 @@ CHANGES
   with an EditForm after save as it was before editing.
   That brings some changes with it:
   - *MAJOR*: unchanged values/fields do not get validated anymore
+    (unless they are empty or are FileUploads)
   - A temporary ``SimpleTerm`` gets created for the missing value
     Title is by default "Missing: ${value}". See MissingTermsMixin.
 

src/z3c/form/validator.py

@@ -89,6 +89,11 @@ class SimpleFieldValidator(StrictSimpleFieldValidator):
 
     def validate(self, value, force=False):
         """See interfaces.IValidator"""
+        if value is self.field.missing_value:
+            # let missing values run into stricter validation
+            # most important case is not let required fields pass
+            return super(SimpleFieldValidator, self).validate(value, force)
+
         if not force:
             if value is interfaces.NOT_CHANGED:
                 # no need to validate unchanged values
@@ -100,7 +105,21 @@ def validate(self, value, force=False):
                 return
 
         # otherwise StrictSimpleFieldValidator will do the job
-        return super(SimpleFieldValidator, self).validate(value)
+        return super(SimpleFieldValidator, self).validate(value, force)
+
+
+class FileUploadValidator(StrictSimpleFieldValidator):
+    """File upload validator
+    """
+    zope.component.adapts(
+        zope.interface.Interface,
+        zope.interface.Interface,
+        zope.interface.Interface,
+        zope.schema.interfaces.IBytes,
+        interfaces.IFileWidget)
+    # only FileUploadDataConverter seems to use NOT_CHANGED, but that needs
+    # to be validated, because file upload is a special case
+    # the most special case if when an ad-hoc IBytes field is required
 
 
 def WidgetValidatorDiscriminators(
@@ -126,6 +145,7 @@ class NoInputData(zope.interface.Invalid):
 
     """
 
+
 class Data(object):
     zope.interface.implements(interfaces.IData)
 

src/z3c/form/validator.txt

@@ -74,7 +74,8 @@ well-defined. Thus, we first need to create a schema.
   ...     login = zope.schema.TextLine(
   ...         title=u'Login',
   ...         min_length=1,
-  ...         max_length=10)
+  ...         max_length=10,
+  ...         required=True)
   ...
   ...     email = zope.schema.TextLine(
   ...         title=u'E-mail')
@@ -186,7 +187,7 @@ again:
   ...     interfaces.IValidator)
 
 Ignoring unchanged values
-~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Most of the time we want to ignore unchanged fields/values at validation.
 A common usecase for this is if a value went away from a vocabulary and we want
@@ -242,6 +243,15 @@ Unless we want to force validation:
   ...
   TooLong: (u'hippocratiusxy', 10)
 
+Some exceptions:
+
+``missing_value`` gets validated
+
+  >>> simple.validate(IPerson['login'].missing_value)
+  Traceback (most recent call last):
+  ...
+  RequiredMissing: login
+
 
 Widget Validators and File-Uploads
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/z3c/form/validator.zcml

@@ -6,6 +6,9 @@
   <adapter
       factory=".validator.SimpleFieldValidator"
       />
+  <adapter
+      factory=".validator.FileUploadValidator"
+      />
   <adapter
       factory=".validator.InvariantsValidator"
       />