Support XPath queries of non-valid XML attribute names

lib/capybara.rb

@@ -393,6 +393,7 @@ module Capybara
   module RackTest; end
   module Selenium; end
 
+  require 'capybara/xpath_patches'
   require 'capybara/helpers'
   require 'capybara/session'
   require 'capybara/window'

lib/capybara/spec/views/form.erb

@@ -648,3 +648,7 @@ New line after and before textarea tag
   <label for="asterisk_input">With Asterisk<abbr title="required">*</abbr></label>
   <input id="asterisk_input" type="number"value="2016"/>
 </p>
+
+<p>
+  <input id="special" {custom}="abcdef" value="custom attribute"/>
+</p>

lib/capybara/xpath_patches.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+module Capybara
+  module XPathPatches
+    module Renderer
+      def attribute(current, name)
+        return super if name =~ /^[a-zA-Z_:][a-zA-Z0-9_:\.\-]*$/
+
+        "#{current}/attribute::*[local-name(.) = #{string_literal(name)}]"
+      end
+    end
+  end
+end
+
+XPath::Renderer.prepend(Capybara::XPathPatches::Renderer)

spec/shared_selenium_session.rb

@@ -445,6 +445,12 @@ RSpec.shared_examples 'Capybara::Session' do |session, mode|
         expect(session).to have_selector(:element, :circle)
         expect(session).to have_selector(:element, :linearGradient, visible: :all)
       end
+
+      it 'can query attributes with strange characters' do
+        session.visit('/form')
+        expect(session).to have_selector(:element, "{custom}": true)
+        expect(session).to have_selector(:element, "{custom}": 'abcdef')
+      end
     end
   end