Support negated classes in the :class filter option

lib/capybara/queries/selector_query.rb

@@ -202,7 +202,11 @@ module Capybara
             XPath.attr(:class)[options[:class]]
           else
             Array(options[:class]).map do |klass|
-              XPath.attr(:class).contains_word(klass)
+              if klass.start_with?('!')
+                !XPath.attr(:class).contains_word(klass.slice(1))
+              else
+                XPath.attr(:class).contains_word(klass)
+              end
             end.reduce(:&)
           end
           expr = "(#{expr})[#{class_xpath}]"
@@ -224,12 +228,18 @@ module Capybara
         css_selectors = expr.split(',').map(&:rstrip)
         expr = css_selectors.map do |sel|
           sel += "##{Capybara::Selector::CSS.escape(options[:id])}" if process_id
-          sel += Array(options[:class]).map { |k| ".#{Capybara::Selector::CSS.escape(k)}" }.join if process_class
+          sel += css_from_classes(Array(options[:class])) if process_class
           sel
         end.join(", ")
         expr
       end
 
+      def css_from_classes(classes)
+        classes = classes.group_by { |c| c.start_with? '!' }
+        (classes[false].to_a.map { |c| ".#{Capybara::Selector::CSS.escape(c)}" } +
+         classes[true].to_a.map { |c| ":not(.#{Capybara::Selector::CSS.escape(c.slice(1))})" }).join
+      end
+
       def apply_expression_filters(expr)
         unapplied_options = options.keys - valid_keys
         expression_filters.inject(expr) do |memo, (name, ef)|

lib/capybara/selector/selector.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+# rubocop:disable Style/AsciiComments
+
 require 'capybara/selector/filter_set'
 require 'capybara/selector/css'
 
@@ -426,3 +428,5 @@ module Capybara
     end
   end
 end
+
+# rubocop:enable Style/AsciiComments

spec/selector_spec.rb

@@ -16,8 +16,8 @@ RSpec.describe Capybara do
                 <h1 class="a">Totally awesome</h1>
                 <p>Yes it is</p>
               </div>
-              <p class="b">Some Content</p>
-              <p class="b"></p>
+              <p class="b c">Some Content</p>
+              <p class="b d"></p>
             </div>
             <div id="#special">
             </div>
@@ -64,7 +64,7 @@ RSpec.describe Capybara do
     it "supports `filter` as an alias for `node_filter`" do
       expect do
         Capybara.add_selector :filter_alias_selector do
-          css { |_unused| "div"}
+          css { |_unused| "div" }
           filter(:something) { |_node, _value| true }
         end
       end.not_to raise_error
@@ -155,6 +155,13 @@ RSpec.describe Capybara do
           expect(string.all(:custom_css_selector, "h1, div", class: 'a').size).to eq 2
         end
 
+        it "handles negated classes" do
+          expect(string.all(:custom_css_selector, "div, p", class: ['b', '!c']).size).to eq 2
+          expect(string.all(:custom_css_selector, "div, p", class: ['!c', '!d', 'b']).size).to eq 1
+          expect(string.all(:custom_xpath_selector, XPath.descendant(:div, :p), class: ['b', '!c']).size).to eq 2
+          expect(string.all(:custom_xpath_selector, XPath.descendant(:div, :p), class: ['!c', '!d', 'b']).size).to eq 1
+        end
+
         it "works with 'special' characters" do
           expect(string.find(:custom_css_selector, "input", class: ".special")[:id]).to eq 'file'
           expect(string.find(:custom_css_selector, "input", class: "2checkbox")[:id]).to eq '2checkbox'