Fix cast when return value is pointer

Author: sue445

_tools/ruby_h_to_go/lib/ruby_h_to_go/function_definition.rb

@@ -110,7 +110,14 @@ def generate_go_content
         go_function_lines << call_c_method
         go_function_lines.push(*after_call_function_lines)
       else
-        go_function_lines << "ret := #{go_function_typeref}(#{call_c_method})"
+        cast_func =
+          if go_function_typeref.start_with?("*")
+            "(#{go_function_typeref})"
+          else
+            go_function_typeref
+          end
+
+        go_function_lines << "ret := #{cast_func}(#{call_c_method})"
         go_function_lines.push(*after_call_function_lines)
         go_function_lines << "return ret"
       end

_tools/ruby_h_to_go/spec/ruby_h_to_go/function_definition_spec.rb

@@ -187,5 +187,36 @@
 
       it { should eq go_content }
     end
+
+    context "rb_errno_ptr" do
+      let(:definition) do
+        RubyHeaderParser::FunctionDefinition.new(
+          name:       "rb_errno_ptr",
+          definition: "int *rb_errno_ptr(void)",
+          filepath:   "/path/to/include/ruby/ruby.h",
+          typeref:    typedef(type: "int", pointer: :ref),
+          args:       [],
+        )
+      end
+
+      let(:go_content) do
+        <<~GO
+          // RbErrnoPtr calls `rb_errno_ptr` in C
+          //
+          // Original definition is following
+          //
+          //	int *rb_errno_ptr(void)
+          //
+          // ref. https://github.com/ruby/ruby/blob/master/include/ruby/ruby.h
+          func RbErrnoPtr() *int {
+          ret := (*int)(C.rb_errno_ptr())
+          return ret
+          }
+
+        GO
+      end
+
+      it { should eq go_content }
+    end
   end
 end

_tools/ruby_h_to_go/spec/ruby_header_parser/parser_spec.rb

@@ -136,6 +136,20 @@
       its(:typeref)    { should eq typedef(type: "int") }
       its(:args)       { should eq args }
     end
+
+    context "rb_errno_ptr" do
+      subject { definitions.find { |d| d.name == "rb_errno_ptr" } }
+
+      let(:args) do
+        []
+      end
+
+      its(:name)       { should eq "rb_errno_ptr" }
+      its(:definition) { should eq "int *rb_errno_ptr(void)" }
+      its(:filepath)   { should be_end_with "/ruby/ruby.h" }
+      its(:typeref)    { should eq typedef(type: "int", pointer: :ref) }
+      its(:args)       { should eq args }
+    end
   end
 
   describe "#extract_static_inline_function_definitions" do