Fixed #169: responds_to? didn't work with generic classes

spec/compiler/codegen/responds_to_spec.cr

@@ -29,4 +29,26 @@ describe "Codegen: responds_to?" do
   it "codegens responds_to? with nilable gives false becuase other type 2" do
     run("class Reference; def foo; end; end; (1 == 2 ? nil : Reference.new).responds_to?(:foo)").to_b.should be_true
   end
+
+  it "codegends responds_to? with generic class (1)" do
+    run(%(
+      class Foo(T)
+        def foo
+        end
+      end
+
+      Foo(Int32).new.responds_to?(:foo)
+      )).to_b.should be_true
+  end
+
+  it "codegends responds_to? with generic class (2)" do
+    run(%(
+      class Foo(T)
+        def foo
+        end
+      end
+
+      Foo(Int32).new.responds_to?(:bar)
+      )).to_b.should be_false
+  end
 end

src/compiler/crystal/types.cr

@@ -1582,6 +1582,10 @@ module Crystal
     delegate :passed_by_value?, @generic_class
     delegate :type_desc, @generic_class
 
+    def filter_by_responds_to(name)
+      @generic_class.filter_by_responds_to(name) ? self : nil
+    end
+
     def class?
       true
     end