Fix stylelint violations when using Tailwind

When we introduced #1148 we did not test it against applications that
invoked `suspenders:styles --css=tailwind`.

lib/generators/suspenders/lint_generator.rb

@@ -21,7 +21,11 @@ def install_gems
       end
 
       def configure_stylelint
-        copy_file "stylelintrc.json", ".stylelintrc.json"
+        if using_tailwind?
+          copy_file "tailwind.stylelintrc.json", ".stylelintrc.json"
+        else
+          copy_file "stylelintrc.json", ".stylelintrc.json"
+        end
       end
 
       def configure_eslint

lib/suspenders/generators.rb

@@ -18,6 +18,10 @@ def default_test_helper_present?
       def rspec_test_helper_present?
         File.exist? Rails.root.join("spec/rails_helper.rb")
       end
+
+      def using_tailwind?
+        File.exist? Rails.root.join("tailwind.config.js")
+      end
     end
 
     module APIAppUnsupported

test/generators/suspenders/lint_generator_test.rb

@@ -53,6 +53,30 @@ class LintGeneratorTest < Rails::Generators::TestCase
         end
       end
 
+      test "configures stylelint for tailwind" do
+        expected_content = <<~TEXT
+          {
+            "extends": "@thoughtbot/stylelint-config",
+            "rules": {
+              "scss/at-rule-no-unknown": [
+                true,
+                {
+                  "ignoreAtRules": ["tailwind"]
+                }
+              ]
+            }
+          }
+        TEXT
+
+        with_css_option :tailwind do
+          capture(:stderr) { run_generator }
+
+          assert_file app_root(".stylelintrc.json") do |file|
+            assert_equal expected_content, file
+          end
+        end
+      end
+
       test "configures eslint" do
         expected_content = <<~JSON
           {

test/test_helper.rb

@@ -100,6 +100,21 @@ def with_test_suite(test_suite, &block)
     remove_dir_if_exists "spec"
   end
 
+  def with_css_option(css, &block)
+    case css
+    when :postcss
+      touch "postcss.config.js"
+    when :tailwind
+      touch "tailwind.config.js"
+    else
+      raise ArgumentError, "unknown css option: #{css.inspect}"
+    end
+    yield
+  ensure
+    remove_file_if_exists "postcss.config.js"
+    remove_file_if_exists "tailwind.config.js"
+  end
+
   def backup_file(file)
     FileUtils.copy app_root(file), app_root("#{file}.bak")
   end