Don't hang when a length range's maximum is Infinity

Raise with a meaningful error message instead. It's
not feasible to allow infinitely large persisted
data structures since there's always some form of
constraint in reality, depending on the datastore
or even the physical amount of memory available.

[#1383 state:resolved]

lib/dm-validations/auto_validate.rb

@@ -132,9 +132,14 @@ def infer_presence_validation_for(property, options)
       def infer_length_validation_for(property, options)
         return unless [ DataMapper::Property::String, DataMapper::Property::Text ].any? { |klass| property.kind_of?(klass) }
 
-        case length = property.options.fetch(:length, DataMapper::Property::String::DEFAULT_LENGTH)
-          when Range then options[:within]  = length
-          else            options[:maximum] = length
+        length = property.options.fetch(:length, DataMapper::Property::String::DEFAULT_LENGTH)
+
+
+        if length.is_a?(Range)
+          raise ArgumentError, "Infinity is no valid upper bound for a length range" if length.last == Infinity
+          options[:within]  = length
+        else
+          options[:maximum] = length
         end
 
         validates_length_of property.name, options_with_message(options, property, :length)

spec/integration/automatic_validation/inferred_length_validation_spec.rb

@@ -122,4 +122,13 @@
       @model.errors.on(:body).should == [ 'Body must be between 1 and 500 characters long' ]
     end
   end
+
+  describe 'with an infinitely long note' do
+    it "should raise when trying to set the upper bound of a property length range to Infinity" do
+      expected_msg = "Infinity is no valid upper bound for a length range"
+      lambda {
+        @model.class.property :body, String, :length => (1..1.0/0)
+      }.should raise_error(ArgumentError, expected_msg)
+    end
+  end
 end