Optimize Kramdown::JekyllDocument#to_html calls

[ashmaroli]

• This is a 🙋 feature or enhancement.
• This is tested by existing coverage.

Summary

By having :to_html explicitly defined for the Kramdown::JekyllDocument instances, the benefits are following:

• Reduce String allocations from converting :to_html to "to_html".
• Reduce MatchData and String allocations from testing and extracting "html" from the method name and consequent conversion into "Html".
• Reduce time spent to require "kramdown/converter/html" and consequent constant-lookup.

The optimization is to bypass steps above and call Kramdown::Converter::Html.convert directly. This is possible because Kramdown::Converter::Html is set up to be autoloaded if not available already.

Context

Prior, I made an attempt to propose this patch at the upstream kramdown core : gettalong/kramdown#644. It got rejected since the change brought little value to the kramdown project.

However, the patch could have relatively more value to Jekyll because:

• Jekyll Core exclusively uses the :to_html method in its conversion process.
• Jekyll sites can have a large no. of Markdown documents being converted to HTML.
• Jekyll sites can have equally large use of the markdownify Liquid filter which under-the-hood uses the same API.

The upstream code as of kramdown-2.1.0 is:

# Check if a method is invoked that begins with +to_+ and if so, try to instantiate a converter
# class (i.e. a class in the Kramdown::Converter module) and use it for converting the document.
#
# For example, +to_html+ would instantiate the Kramdown::Converter::Html class.
def method_missing(id, *attr, &block)
  if id.to_s =~ /^to_(\w+)$/ && (name = Utils.camelize($1)) &&
      try_require('converter', name) && Converter.const_defined?(name)
    output, warnings = Converter.const_get(name).convert(@root, @options)
    @warnings.concat(warnings)
    output
  else
    super
  end
end

[DirtyF]

Memory Profile Summary

--- master https://travis-ci.org/jekyll/jekyll/jobs/657343689
+++ PR     https://travis-ci.org/jekyll/jekyll/jobs/657363607

- Total allocated: 356.24 MB (3209407 objects)
+ Total allocated: 355.73 MB (3200658 objects)
  Total retained:  18.88 MB (107272 objects)

[DirtyF]

Awesome!

[ashmaroli]

@jekyllbot: merge +minor