Fix classes that extend modules where contracts were included

lib/contracts/core.rb

@@ -24,13 +24,22 @@ def functype(funcname)
         end
       end
 
-      base.class_eval do
+      # NOTE: Workaround for `defined?(super)` bug in ruby 1.9.2
+      # source: http://stackoverflow.com/a/11181685
+      # bug: https://bugs.ruby-lang.org/issues/6644
+      base.class_eval <<-RUBY
         # TODO: deprecate
         # Required when contracts are included in global scope
         def Contract(*args)
-          self.class.Contract(*args)
+          if defined?(super)
+            super
+          else
+            self.class.Contract(*args)
+          end
         end
+      RUBY
 
+      base.class_eval do
         def functype(funcname)
           contracts = Engine.fetch_from(self.class).decorated_methods_for(:instance_methods, funcname)
           if contracts.nil?

spec/contracts_spec.rb

@@ -717,4 +717,33 @@ def delim(match)
       expect { c.double("asd") }.to raise_error
     end
   end
+
+  describe "classes with extended modules" do
+    let(:klass) do
+      m = Module.new do
+        include Contracts::Core
+      end
+
+      Class.new do
+        include Contracts::Core
+        extend m
+
+        Contract String => nil
+        def foo(x)
+        end
+      end
+    end
+
+    it "is possible to define it" do
+      expect { klass }.not_to raise_error
+    end
+
+    it "works correctly with methods with passing contracts" do
+      expect { klass.new.foo("bar") }.not_to raise_error
+    end
+
+    it "works correctly with methods with passing contracts" do
+      expect { klass.new.foo(42) }.to raise_error(ContractError, /Expected: String/)
+    end
+  end
 end