fixes issue #242 - contract's return value is now enforced with blocks properly

Gemfile

@@ -6,7 +6,7 @@ group :test do
   gem "rspec"
   gem "aruba"
   gem "cucumber", "~> 1.3.20"
-  gem "rubocop", "~> 0.29.1", :platform => [:ruby_20, :ruby_21, :ruby_22, :ruby_23]
+  gem "rubocop", "~> 0.29.1" if RUBY_VERSION >= "2"
 end
 
 group :development do

lib/contracts/call_with.rb

@@ -26,7 +26,9 @@ def call_with(this, *args, &blk)
                                                   :return_value => false)
         end
 
-        if contract.is_a?(Contracts::Func)
+        if contract.is_a?(Contracts::Func) && blk && !nil_block_appended
+          blk = Contract.new(klass, arg, *contract.contracts)
+        elsif contract.is_a?(Contracts::Func)
           args[i] = Contract.new(klass, arg, *contract.contracts)
         end
       end
@@ -73,7 +75,8 @@ def call_with(this, *args, &blk)
                  method.call(*args, &blk)
                else
                  # original method name referrence
-                 method.send_to(this, *args, &blk)
+                 added_block = blk ? lambda { |*params| blk.call(*params) } : nil
+                 method.send_to(this, *args, &added_block)
                end
 
       unless @ret_validator[result]

spec/methods_spec.rb

@@ -0,0 +1,54 @@
+RSpec.describe "Contracts:" do
+  describe "method called with blocks" do
+    module FuncTest
+      include Contracts::Core
+      include Contracts::Builtin
+
+      Contract Func[Num=>Num] => nil
+      def foo(&blk)
+        _ = blk.call(2)
+        nil
+      end
+
+      Contract Num, Func[Num=>Num] => nil
+      def foo2(a, &blk)
+        _ = blk.call(2)
+        nil
+      end
+
+      Contract Func[Num=>Num] => nil
+      def bar(blk)
+        _ = blk.call(2)
+        nil
+      end
+
+      Contract Num, Func[Num=>Num] => nil
+      def bar2(a, blk)
+        _ = blk.call(2)
+        nil
+      end
+    end
+
+    def obj
+      Object.new.tap do |o|
+        o.extend(FuncTest)
+      end
+    end
+
+    it "should enforce return value inside block with no other parameter" do
+      expect { obj.foo(&:to_s) }.to raise_error
+    end
+
+    it "should enforce return value inside block with other parameter" do
+      expect { obj.foo2(2) { |x| x.to_s } }.to raise_error
+    end
+
+    it "should enforce return value inside lambda with no other parameter" do
+      expect { obj.bar lambda { |x| x.to_s } }.to raise_error
+    end
+
+    it "should enforce return value inside lambda with other parameter" do
+      expect { obj.bar2(2, lambda { |x| x.to_s }) }.to raise_error
+    end
+  end
+end