Fix environment file loader (#1340)

* Extract Puma::Configuration#config_files method and add few unit tests

* Add TestConfigFile#test_config_files_with_rack_env test

* Fix configuration loading based on RACK_ENV

* Add test case when config files files are not specified

* Refactor Puma::Configuration#config_files method

* Fix backwards compatibility issue.
Environment could be a String or Proc

lib/puma/configuration.rb

@@ -189,22 +189,22 @@ def puma_default_options
     end
 
     def load
+      config_files.each { |config_file| @file_dsl._load_from(config_file) }
+
+      @options
+    end
+
+    def config_files
       files = @options.all_of(:config_files)
 
-      if files.empty?
-        imp = %W(config/puma/#{@options[:environment]}.rb config/puma.rb).find { |f|
-          File.exist?(f)
-        }
+      return [] if files == ['-']
+      return files if files.any?
 
-        files << imp
-      elsif files == ["-"]
-        files = []
+      first_default_file = %W(config/puma/#{environment_str}.rb config/puma.rb).find do |f|
+        File.exist?(f)
       end
 
-      files.each do |f|
-        @file_dsl._load_from(f)
-      end
-      @options
+      [first_default_file]
     end
 
     # Call once all configuration (included from rackup files)
@@ -264,6 +264,10 @@ def environment
       @options[:environment]
     end
 
+    def environment_str
+      environment.respond_to?(:call) ? environment.call : environment
+    end
+
     def load_plugin(name)
       @plugins.create name
     end

test/test_config.rb

@@ -3,6 +3,11 @@
 require "puma/configuration"
 
 class TestConfigFile < Minitest::Test
+  def setup
+    FileUtils.mkpath("config/puma")
+    File.write("config/puma/fake-env.rb", "")
+  end
+
   def test_app_from_rackup
     conf = Puma::Configuration.new do |c|
       c.rackup "test/rackup/hello-bind.ru"
@@ -84,6 +89,56 @@ def test_parameters_overwrite_files
     assert_equal 5, conf.options[:max_threads]
   end
 
+  def test_config_files_default
+    conf = Puma::Configuration.new do
+    end
+
+    assert_equal [nil], conf.config_files
+  end
+
+  def test_config_files_with_dash
+    conf = Puma::Configuration.new(config_files: ['-']) do
+    end
+
+    assert_equal [], conf.config_files
+  end
+
+  def test_config_files_with_existing_path
+    conf = Puma::Configuration.new(config_files: ['test/config/settings.rb']) do
+    end
+
+    assert_equal ['test/config/settings.rb'], conf.config_files
+  end
+
+  def test_config_files_with_non_existing_path
+    conf = Puma::Configuration.new(config_files: ['test/config/typo/settings.rb']) do
+    end
+
+    assert_equal ['test/config/typo/settings.rb'], conf.config_files
+  end
+
+  def test_config_files_with_rack_env
+    with_env('RACK_ENV' => 'fake-env') do
+      conf = Puma::Configuration.new do
+      end
+
+      assert_equal ['config/puma/fake-env.rb'], conf.config_files
+    end
+  end
+
+  def test_config_files_with_specified_environment
+    conf = Puma::Configuration.new do
+    end
+
+    conf.options[:environment] = 'fake-env'
+
+    assert_equal ['config/puma/fake-env.rb'], conf.config_files
+  end
+
+  def teardown
+    FileUtils.rm_r("config/puma")
+  end
+
   private
 
     def with_env(env = {})