class Jekyll::Tags::PostUrl

def initialize(tag_name, post, tokens)
  super
  @orig_post = post.strip
  begin
    @post = PostComparer.new(@orig_post)
  rescue StandardError => e
    raise Jekyll::Errors::PostURLError, <<~MSG
      Could not parse name of post "#{@orig_post}" in tag 'post_url'.
       Make sure the post exists and the name is correct.
       #{e.class}: #{e.message}
    MSG
  end
end

def render(context)
  @context = context
  site = context.registers[:site]
  site.posts.docs.each do |document|
    return relative_url(document) if @post == document
  end
  # New matching method did not match, fall back to old method
  # with deprecation warning if this matches
  site.posts.docs.each do |document|
    next unless @post.deprecated_equality document
    Jekyll::Deprecator.deprecation_message(
      "A call to '{% post_url #{@post.name} %}' did not match a post using the new " \
      "matching method of checking name (path-date-slug) equality. Please make sure " \
      "that you change this tag to match the post's name exactly."
    )
    return relative_url(document)
  end
  raise Jekyll::Errors::PostURLError, <<~MSG
    Could not find post "#{@orig_post}" in tag 'post_url'.
    Make sure the post exists and the name is correct.
  MSG
end