Allow custom postcss.config.js

README.md

@@ -38,7 +38,6 @@ This also works with relative paths. If you've installed into your app's directo
 TAILWINDCSS_INSTALL_DIR=node_modules/.bin
 ```
 
-
 ## Developing with Tailwindcss
 
 ### Configuration
@@ -100,6 +99,24 @@ If you want unminified assets, you can pass a `debug` argument to the rake task,
 Note that you can combine task options, e.g. `rails tailwindcss:watch[debug,poll]`.
 
 
+### Using with PostCSS
+
+If you want to use PostCSS as a preprocessor, create a custom `config/postcss.config.js` and it will be loaded automatically.
+
+For example, to enable nesting:
+
+```js
+// config/postcss.config.js
+module.exports = {
+  plugins: {
+    'postcss-import': {},
+    'tailwindcss/nesting': {},
+    tailwindcss: {},
+    autoprefixer: {},
+  },
+}
+```
+
 ### Custom inputs or outputs
 
 If you need to use a custom input or output file, you can run `bundle exec tailwindcss` to access the platform-specific executable, and give it your own build options.

lib/tailwindcss/commands.rb

@@ -74,14 +74,19 @@ def executable(exe_path: DEFAULT_DIR)
       end
 
       def compile_command(debug: false, **kwargs)
-        [
+        command = [
           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,
-        ].tap do |command|
-          command << "--minify" unless (debug || rails_css_compressor?)
-        end
+        ]
+
+        command << "--minify" unless (debug || rails_css_compressor?)
+
+        postcss_path = Rails.root.join("config/postcss.config.js")
+        command += ["--postcss", postcss_path.to_s] if File.exist?(postcss_path)
+
+        command
       end
 
       def watch_command(always: false, poll: false, **kwargs)

test/lib/tailwindcss/commands_test.rb

@@ -151,6 +151,29 @@ def mock_local_tailwindcss_install
     end
   end
 
+  test ".compile_command when postcss.config.js exists" do
+    mock_exe_directory("sparc-solaris2.8") do |dir, executable|
+      Dir.mktmpdir do |tmpdir|
+        Rails.stub(:root, Pathname.new(tmpdir))  do # Rails.root won't work in this test suite
+          actual = Tailwindcss::Commands.compile_command(exe_path: dir)
+          assert_kind_of(Array, actual)
+          assert_equal(executable, actual.first)
+          refute_includes(actual, "--postcss")
+
+          config_file = Rails.root.join("config/postcss.config.js")
+          FileUtils.mkdir_p(Rails.root.join("config"))
+          FileUtils.touch(config_file)
+          actual = Tailwindcss::Commands.compile_command(exe_path: dir)
+          assert_kind_of(Array, actual)
+          assert_equal(executable, actual.first)
+          assert_includes(actual, "--postcss")
+          postcss_index = actual.index("--postcss")
+          assert_equal(actual[postcss_index + 1], config_file.to_s)
+        end
+      end
+    end
+  end
+
   test ".watch_command" do
     mock_exe_directory("sparc-solaris2.8") do |dir, executable|
       Rails.stub(:root, File) do # Rails.root won't work in this test suite