[feature] using "of complex-selector-list" for `:nth-child` and `:nth-last-child` #3080

G-Rath · 2023-12-26T20:51:09Z

G-Rath
Dec 26, 2023

Please describe the bug

:nth-child and :nth-last-child support an optional "of " argument, which currently results in an error with nokogiri.

Help us reproduce what you're seeing

#! /usr/bin/env ruby

require 'nokogiri'
require 'minitest/autorun'

class Test < Minitest::Spec
  describe "Node#css" do
    it "should find a div using chained classes" do
      html = <<~HEREDOC
        <html>
          <body>
            <span>hello world!</span>
            <div class="foo"> one</div>
            <div class="bar">two</div>
            <div class="foo bar">three</div>
      HEREDOC

      doc = Nokogiri::HTML::Document.parse(html)

      assert_equal "two", doc.css(':nth-child(2 of div)').text
      assert_equal 1, doc.css("div.foo.bar").length
      assert_equal "three", doc.at_css("div.foo.bar").text
    end
  end
end

❯ bundle exec rails test test/my_test.rb
Run options: --seed 16242

# Running:

E

Error:
Node#css#test_0001_should find a div using chained classes:
Nokogiri::CSS::SyntaxError: unexpected ' ' after '2'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/lib/nokogiri/css/parser_extras.rb:86:in `on_error'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/racc-1.7.3/lib/racc/parser.rb:267:in `_racc_do_parse_c'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/racc-1.7.3/lib/racc/parser.rb:267:in `do_parse'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/lib/nokogiri/css/parser_extras.rb:68:in `parse'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/lib/nokogiri/css/parser_extras.rb:78:in `xpath_for'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/lib/nokogiri/css.rb:52:in `xpath_for'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/lib/nokogiri/xml/searchable.rb:251:in `block in xpath_query_from_css_rule'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/lib/nokogiri/xml/searchable.rb:250:in `map'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/lib/nokogiri/xml/searchable.rb:250:in `xpath_query_from_css_rule'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/lib/nokogiri/xml/searchable.rb:242:in `block in css_rules_to_xpath'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/lib/nokogiri/xml/searchable.rb:242:in `map'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/lib/nokogiri/xml/searchable.rb:242:in `css_rules_to_xpath'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/lib/nokogiri/xml/searchable.rb:211:in `css_internal'
    /home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/lib/nokogiri/xml/searchable.rb:132:in `css'
    /home/jones/workspace/projects/my_app/test/my_test.rb:20:in `block (2 levels) in <class:Test>'


bin/rails test /home/jones/workspace/projects/my_app/test/my_test.rb:8



Finished in 0.006674s, 149.8387 runs/s, 0.0000 assertions/s.
1 runs, 0 assertions, 0 failures, 1 errors, 0 skips

Expected behavior

It passes

Environment

# Nokogiri (1.15.5)
    ---
    warnings: []
    nokogiri:
      version: 1.15.5
      cppflags:
      - "-I/home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/ext/nokogiri"
      - "-I/home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/ext/nokogiri/include"
      - "-I/home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/ext/nokogiri/include/libxml2"
      ldflags: []
    ruby:
      version: 3.1.4
      platform: x86_64-linux
      gem_platform: x86_64-linux
      description: ruby 3.1.4p223 (2023-03-30 revision 957bb7cb81) [x86_64-linux]
      engine: ruby
    libxml:
      source: packaged
      precompiled: true
      patches:
      - 0001-Remove-script-macro-support.patch
      - 0002-Update-entities-to-remove-handling-of-ssi.patch
      - 0003-libxml2.la-is-in-top_builddir.patch
      - '0009-allow-wildcard-namespaces.patch'
      - 0010-update-config.guess-and-config.sub-for-libxml2.patch
      - 0011-rip-out-libxml2-s-libc_single_threaded-support.patch
      libxml2_path: "/home/jones/.rbenv/versions/3.1.4/lib/ruby/gems/3.1.0/gems/nokogiri-1.15.5-x86_64-linux/ext/nokogiri"
      memory_management: ruby
      iconv_enabled: true
      compiled: 2.11.6
      loaded: 2.11.6
    libxslt:
      source: packaged
      precompiled: true
      patches:
      - 0001-update-config.guess-and-config.sub-for-libxslt.patch
      datetime_enabled: true
      compiled: 1.1.39
      loaded: 1.1.39
    other_libraries:
      zlib: 1.2.13
      libgumbo: 1.0.0-nokogiri

Additional context

I've confirmed this works in a real browser:

flavorjones · 2023-12-27T02:55:36Z

flavorjones
Dec 27, 2023
Maintainer

This would be a great feature to add! If you're interested in implementing it, I would be happy to give some suggestions and review a pull request.

However, I won't be able to spend time implementing this myself anytime soon. Please let me know how I can help you contribute!

3 replies

flavorjones Dec 27, 2023
Maintainer

I've converted this to a discussion under the "feature request" section.

G-Rath Dec 27, 2023
Author

Sweet - if you have the time to provide some pointers, I'm happy to try taking a look; this isn't critical for me and I've not done a lot of work in this space so depending on the complexity I might not be able to pick it up straight away, but I expect any pointers given would be useful for anyone looking to pick this up :)

flavorjones Dec 28, 2023
Maintainer

Nokogiri has a subsystem to parse CSS queries and "compile" them into XPath queries, and to be honest it's not terribly easy to contribute to today (which is why the CSS syntax support has lagged so much over the last decade).

The long game is to split out this concern into a separate gem, and if possible swap out our hand-written CSS parser in favor of something a bit better-maintained. I started writing some thoughts in mid-2022 here: #2560

I think maybe the right thing to do is for me to schedule some time to do this structural work, and then the CSS parsing/compilation should be easier to contribute to.

That said, if you want to take a whack at it, take a look at:

the tests in test/css
the files in lib/nokogiri/css

In particular, parser.y and tokenizer.rex is where the grammar/syntax is defined, and xpath_visitor.rb is where most of the conversion to XPath happens.

My best advice would be to start with the grammar, and if you can extend it so that it generates an AST that visit_function() receives, the rest is Just Ruby™ and writing tests to make sure we've implemented the XPath correctly.

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[feature] using "of complex-selector-list" for :nth-child and :nth-last-child #3080

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[feature] using "of complex-selector-list" for `:nth-child` and `:nth-last-child` #3080

G-Rath
Dec 26, 2023

Replies: 1 comment 3 replies

flavorjones
Dec 27, 2023
Maintainer

flavorjones Dec 27, 2023
Maintainer

G-Rath Dec 27, 2023
Author

flavorjones Dec 28, 2023
Maintainer