Add support for module prepended blocks

- Added `prepend_features` method to Tins concern
- Updated ConcernTest to test prepend feature
- Raise StandardError for duplicate block definitions for included and
  prepended blocks

lib/tins/concern.rb

@@ -19,14 +19,41 @@ def append_features(base)
       end
     end
 
+    def prepend_features(base)
+      if base.instance_variable_defined?("@_dependencies")
+        base.instance_variable_get("@_dependencies") << self
+        false
+      else
+        return false if base < self
+        @_dependencies.each { |dep| base.send(:include, dep) }
+        super
+        base.extend const_get("ClassMethods") if const_defined?("ClassMethods")
+        base.class_eval(&@_prepended_block) if instance_variable_defined?("@_prepended_block")
+        Thread.current[:tin_concern_args] = nil
+        true
+      end
+    end
+
     def included(base = nil, &block)
       if base.nil?
+        instance_variable_defined?(:@_included_block) and
+          raise StandardError, "included block already defined"
         @_included_block = block
       else
         super
       end
     end
 
+    def prepended(base = nil, &block)
+      if base.nil?
+        instance_variable_defined?(:@_prepended_block) and
+          raise StandardError, "prepended block already defined"
+        @_prepended_block = block
+      else
+        super
+      end
+    end
+
     def class_methods(&block)
       modul = const_get(:ClassMethods) if const_defined?(:ClassMethods, false)
       unless modul

tests/concern_test.rb

@@ -8,6 +8,10 @@ module AC
       $included = self
     end
 
+    prepended do
+      $prepended = self
+    end
+
     def foo
       :foo
     end
@@ -32,17 +36,37 @@ def baz2
   end
 
   $included = nil
+  $prepended = nil
 
   class A
     include AC
   end
 
-  def test_concern
+  class B
+    prepend AC
+  end
+
+  def test_concern_include
     a = A.new
     assert_equal A, $included
     assert_equal :foo, a.foo
     assert_equal :bar, A.bar
     assert_equal :baz1, A.baz1
     assert_equal :baz2, A.baz2
+    assert_raise(StandardError) do
+      AC.module_eval { included {} }
+    end
+  end
+
+  def test_concern_prepend
+    a = B.new
+    assert_equal B, $prepended
+    assert_equal :foo, a.foo
+    assert_equal :bar, B.bar
+    assert_equal :baz1, B.baz1
+    assert_equal :baz2, B.baz2
+    assert_raise(StandardError) do
+      AC.module_eval { prepended {} }
+    end
   end
 end