Add support for Tailwind CSS v4

which doesn't need a config file or an input file anymore.

Closes #419

lib/tailwindcss/commands.rb

@@ -3,14 +3,23 @@
 module Tailwindcss
   module Commands
     class << self
+      def tailwindcss_version
+        Tailwindcss::Ruby::VERSION
+      end
+
       def compile_command(debug: false, **kwargs)
         command = [
           Tailwindcss::Ruby.executable(**kwargs),
-          "-i", Rails.root.join("app/assets/stylesheets/application.tailwind.css").to_s,
-          "-o", Rails.root.join("app/assets/builds/tailwind.css").to_s,
-          "-c", Rails.root.join("config/tailwind.config.js").to_s,
+          "-o", Rails.root.join("app/assets/builds/tailwind.css").to_s
         ]
 
+        unless tailwindcss_version >= "4.0"
+          command += [
+            "-i", Rails.root.join("app/assets/stylesheets/application.tailwind.css").to_s,
+            "-c", Rails.root.join("config/tailwind.config.js").to_s,
+          ]
+        end
+
         command << "--minify" unless (debug || rails_css_compressor?)
 
         postcss_path = Rails.root.join("config/postcss.config.js")

test/lib/tailwindcss/commands_test.rb

@@ -9,7 +9,33 @@ def setup
     @executable = Tailwindcss::Ruby.executable
   end
 
-  test ".compile_command" do
+  test ".compile_command with tailwindcss v3" do
+    Rails.stub(:root, File) do # Rails.root won't work in this test suite
+      Tailwindcss::Commands.stub(:tailwindcss_version, "3.4.13") do
+        actual = Tailwindcss::Commands.compile_command
+        assert_kind_of(Array, actual)
+        assert_equal(executable, actual.first)
+        assert_includes(actual, "-i")
+        assert_includes(actual, "-c")
+        assert_includes(actual, "-o")
+      end
+    end
+  end
+
+  test ".compile_command with tailwindcss v4" do
+    Rails.stub(:root, File) do # Rails.root won't work in this test suite
+      Tailwindcss::Commands.stub(:tailwindcss_version, "4.0.0") do
+        actual = Tailwindcss::Commands.compile_command
+        assert_kind_of(Array, actual)
+        assert_equal(executable, actual.first)
+        refute_includes(actual, "-i")
+        refute_includes(actual, "-c")
+        assert_includes(actual, "-o")
+      end
+    end
+  end
+
+  test ".compile_command debug flag" do
     Rails.stub(:root, File) do # Rails.root won't work in this test suite
       actual = Tailwindcss::Commands.compile_command
       assert_kind_of(Array, actual)