Ruby nested msg caps (#5564)

* Ruby nested msg caps

* nested types tests added

* test cases added for RubifyConstant

* extracted NestedMessage to TestNestedMessage

* removed nested tests with leading underscore

* extracted testLowercase to toplevel testLowercaseNested

ruby/tests/generated_code.proto

@@ -69,6 +69,11 @@ enum TestEnum {
   C = 3;
 }
 
+message testLowercaseNested {
+  message lowercase{}
+}
+
+
 message TestUnknown {
   TestUnknown optional_unknown = 11;
   repeated TestUnknown repeated_unknown = 31;

ruby/tests/generated_code_test.rb

@@ -15,6 +15,8 @@ class GeneratedCodeTest < Test::Unit::TestCase
     # successfully creates message definitions and classes, not to test every
     # aspect of the extension (basic.rb is for that).
     A::B::C::TestMessage.new
+    A::B::C::TestMessage::NestedMessage.new
+    A::B::C::TestLowercaseNested::Lowercase.new
     FooBar::TestImportedMessage.new
     A::B::TestRubyPackageMessage.new
   end

src/google/protobuf/compiler/ruby/ruby_generator.cc

@@ -389,7 +389,7 @@ void GenerateMessageAssignment(
     "lookup(\"$full_name$\").msgclass\n",
     "full_name", message->full_name());
 
-  std::string nested_prefix = prefix + message->name() + "::";
+  std::string nested_prefix = prefix + RubifyConstant(message->name()) + "::";
   for (int i = 0; i < message->nested_type_count(); i++) {
     GenerateMessageAssignment(nested_prefix, message->nested_type(i), printer);
   }