Updating test and README for custom postcss.config.js

Author: ahmeij

Diff for: README.md

@@ -38,6 +38,20 @@ This also works with relative paths. If you've installed into your app's directo
 TAILWINDCSS_INSTALL_DIR=node_modules/.bin
 ```
 
+### Using a custom postcss.config.js
+
+If you want to use a custom `postcss.config.js`, for example to enable nesting, you can place it in the `config` folder and it will be loaded automatically.
+
+```
+module.exports = {
+  plugins: {
+    'postcss-import': {},
+    'tailwindcss/nesting': {},
+    tailwindcss: {},
+    autoprefixer: {},
+  },
+}
+```
 
 ## Developing with Tailwindcss
 

Diff for: test/lib/tailwindcss/commands_test.rb

@@ -151,6 +151,27 @@ 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/postcss.config.js")
+
+          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 #{config_file}")
+        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