fix: support Encoding class for xml write_to

[ellaklara]

What problem is this PR intended to solve?

Fixes #2774

Have you included adequate test coverage?

The PR adds two tests that cover both setting encoding with a string and the Encoding class.

Question

I discovered that the html5 node write_to (lib/nokogiri/html5/node.rb) also doesn't support the Encoding class, is this something you'd like me to add as well? Where would be a good place to test this? I couldn't find any encoding tests for this class.

[flavorjones]

@ellaklara Thank you for contributing this! I've kicked off CI. I think we should support this in the HTML5 version as well. If there aren't tests we should definitely add that coverage. I'll take a deeper look in the next day or so.

[flavorjones]

OK! I've looked into this a bit more, which was good for me because the tests for serialization encoding are somewhat implicit and sort of spread all over the place, so I'd like to add a bunch of test coverage to go along with this.

So backing up for a minute to re-describe the problem from #2774 in a bit more detail, #write_to isn't the only method we need to ensure supports Encoding objects, it's the whole set of serialization methods. At a minimum this includes:

• Node#write_to
• Node#serialize
• Node#to_html
• Node#to_xml
• Node#to_xhtml

And as you pointed out, we also need to test the HTML5 patch for serialization that lives in lib/nokogiri/html5/node.rb. That code's encoding handling is tested in test/html5/test_encoding.rb and test/html5/test_api.rb.

So I think the approach to testing I'd like to take is:

• write some thorough explicit tests for the current encoding behavior
• then add some tests for Encoding (similar to what you have, but more)
• and then make the tests pass

Let me add a commit to this PR with some explicit tests for the current behavior, if you don't mind? Then, if you're up for it, I'd love for you to add the Encoding tests for the other methods and finish the feature!

[flavorjones]

Aaaand of course I think I'm finding encoding bugs while writing these tests. 😬

[flavorjones]

OK, bug report filed at #2801

But I think that's not material to what we're trying to do in this PR! So ... onward

[flavorjones]

@ellaklara OK! I've added a commit on this PR (before yours) that introduces a new file, test/test_serialization_encoding.rb that has some coverage for encoded output for XML, HTML4, and HTML5 serialization methods.

Again, only if you're up for it, it would be great to add Encoding tests there, and make sure they work for all those classes and methods. Let me know either way! ❤️

[flavorjones]

I'm working on the failing JRuby tests, so don't worry about those!

Edit: see #2803, I've rebased this PR on top of those commits.

[flavorjones]

@ellaklara It's been about a week, so I'm going to go ahead and finish the work you so awesomely started! Will be sure to credit you in the CHANGELOG!

[flavorjones]

Thank you, @ellaklara !