Fix a bug that kept us from adding the markdown attribute to HTML tags that contain valid markdown when parsing HTML

[boblail]

You can reproduce the bug like this:

html = <<~HTML
<div>
  <img src="src.png" alt="alt" />
</div>
HTML

markdown = Kramdown::Document.new(html, input: :html).to_kramdown
# => "<div>\n![alt](src.png)\n</div>"

html = Kramdown::Document.new(markdown).to_html
# => "<div>\n![alt](src.png)\n</div>\n\n"

The bug is that the call to to_kramdown converted the IMG tag but did not add markdown="1" to the DIV tag.

As of Kramdown 2.1.0, the markdown attribute is added if the IMG tag is wrapped in a paragraph; and you can see that when the markdown attribute is present, the HTML roundtrips successfully:

html = <<~HTML
<div>
  <p><img src="src.png" alt="alt" /></p>
</div>
HTML

markdown = Kramdown::Document.new(html, input: :html).to_kramdown
# => "<div markdown=\"1\">\n![alt](src.png)\n</div>"

html = Kramdown::Document.new(markdown).to_html
# => "<div>\n  <p><img src=\"src.png\" alt=\"alt\" /></p>\n\n</div>"

[ashmaroli]

[:entity, :text, :html_element] is a static array. In order to avoid repeated allocations of this array on multiple iterations, I recommend hoisting the array as a private constant:

TYPES_ARRAY = [:entity, :text, :html_element]
private_constant :TYPES_ARRAY

def convert_html_element(el, opts)
  markdown_attr = el.options[:category] == :block && el.children.any? do |c|
    ...
    c.children.none? { |t| !TYPES_ARRAY.include?(t.type) }
    ...
  end
end

[gettalong]

How did you determine these three element types?

[boblail]

@gettalong, I added element types until the rest of the Kramdown spec suite passed without changes. 😄

---

I considered

c.children.none? { |t| MARKDOWN_TYPES.member?(t.type) }

instead of

c.children.none? { |t| !NON_MARKDOWN_TYPES.member?(t.type) }

but I think the list would be longer.

[ghepting]

Nice bug fix @boblail! :)

[boblail]

@gettalong, is this OK to merge? Or did you have any followup questions?

[gettalong]

Thank you for your contribution - I have cherry-picked your commit and adapted it a bit.