Make intra-doc refs work when validating with :fragment

Here's a weird corner-case for you: when calling JSON::Validator.validate
and using the :fragment option, any references to other parts of the same
schema would fail.  Why?  Because the handling of :fragment involved
creating a *new* schema, with a new URI, with a subset of the original
schema.  Internal refs (as handled by JSON::Schema::RefAttribute) would try
to resolve the ref within this sub-schema, and go *fwackoom* because the
structure of the sub-schema wouldn't have the right path in it.

I've adjusted the code for schema_from_fragment to not call
initialize_schema (and hence not create those new sub-schemas), and instead
just create a new JSON::Schema object (which, according to the comments, is
the only reason that initialize_schema was being called).  This causes no
new schemas to be created, and RefAttribute can go looking up its ref in the
right place.

lib/json-schema/validator.rb

@@ -186,6 +186,7 @@ def initialize(schema_data, data, opts={})
     end
 
     def schema_from_fragment(base_schema, fragment)
+      schema_uri = base_schema.uri
       fragments = fragment.split("/")
 
       # ensure the first element was a hash, per the fragment spec
@@ -198,17 +199,17 @@ def schema_from_fragment(base_schema, fragment)
           if !base_schema.schema.has_key?(f)
             raise JSON::Schema::SchemaError.new("Invalid fragment resolution for :fragment option")
           end
-        base_schema = base_schema.schema[f]
+          base_schema = base_schema.schema[f]
         elsif base_schema.is_a?(Hash)
           if !base_schema.has_key?(f)
             raise JSON::Schema::SchemaError.new("Invalid fragment resolution for :fragment option")
           end
-        base_schema = initialize_schema(base_schema[f]) #need to return a Schema instance for validation to work
+          base_schema = JSON::Schema.new(base_schema[f],schema_uri,@options[:version])
         elsif base_schema.is_a?(Array)
           if base_schema[f.to_i].nil?
             raise JSON::Schema::SchemaError.new("Invalid fragment resolution for :fragment option")
           end
-        base_schema = initialize_schema(base_schema[f.to_i])
+          base_schema = JSON::Schema.new(base_schema[f.to_i],schema_uri,@options[:version])
         else
           raise JSON::Schema::SchemaError.new("Invalid schema encountered when resolving :fragment option")
         end

test/test_fragment_validation_with_ref.rb

@@ -0,0 +1,40 @@
+require File.expand_path('../test_helper', __FILE__)
+require 'json-schema'
+
+class FragmentValidationWithRef < Test::Unit::TestCase
+  def whole_schema
+    {
+      "$schema" => "http://json-schema.org/draft-04/schema#",
+      "type" => "object",
+      "definitions" => {
+        "post" => {
+          "type" => "object",
+          "properties" => {
+            "content" => {
+              "type" => "string"
+            },
+            "author" => {
+              "type" => "string"
+            }
+          }
+        },
+        "posts" => {
+          "type" => "array",
+          "items" => {
+            "$ref" => "#/definitions/post"
+          }
+        }
+      }
+    }
+  end
+
+  def test_validation_of_fragment
+    data = [{"content" => "ohai", "author" => "Bob"}]
+    v = nil
+    assert_nothing_raised do
+      v = JSON::Validator.fully_validate(whole_schema,data,:fragment => "#/definitions/posts")
+    end
+
+    assert(v.empty?, v.join("\n"))
+  end
+end

test/test_helper.rb

@@ -0,0 +1,2 @@
+require 'test/unit'
+$:.unshift(File.expand_path('../../lib', __FILE__))