Implement `layout' run control keyword

Allow configuration of the layout by specifying either a class or an
instance.

features/run_control/layout.feature

@@ -0,0 +1,27 @@
+Feature: `layout' run control keyword
+
+  Background:
+    Given a file named my_layout.rb with:
+      """
+      class MyLayout
+        def register *_
+          puts "testing_rc_layout"
+        end
+      end
+      """
+
+  Scenario: configures a layout class
+    Given a run control file with:
+      """
+      layout MyLayout
+      """
+    When I run uhwm with options -r./my_layout
+    Then the output must contain "testing_rc_layout"
+
+  Scenario: configures a layout instance
+    Given a run control file with:
+      """
+      layout MyLayout.new
+      """
+    When I run uhwm with options -r./my_layout
+    Then the output must contain "testing_rc_layout"

lib/uh/wm/env.rb

@@ -21,8 +21,8 @@ module Uh
       def_delegators  :@output, :print, :puts
 
       attr_reader   :output, :keybinds
-      attr_accessor :verbose, :debug, :rc_path, :layout_class, :modifier,
+      attr_accessor :verbose, :debug, :rc_path, :modifier, :worker,
-                    :worker
+                    :layout, :layout_class
 
       def initialize output
         @output   = output

lib/uh/wm/run_control.rb

@@ -32,6 +32,14 @@ module Uh
         @env.keybinds[translate_keysym *keysyms] = block
       end
 
+      def layout obj
+        if obj.is_a? Class
+          @env.layout_class = obj
+        else
+          @env.layout = obj
+        end
+      end
+
       def worker type, **options
         @env.worker = [type, options]
       end

spec/uh/wm/env_spec.rb

@@ -70,19 +70,27 @@ module Uh
       end
 
       describe '#layout' do
-        context 'when a layout class is set' do
+        let(:some_layout_class) { Class.new }
-          let(:some_layout) { Class.new }
 
-          before { env.layout_class = some_layout }
+        it 'returns the default layout' do
+          expect(env.layout).to be_an_instance_of ::Uh::Layout
+        end
+
+        context 'when a layout is set' do
+          let(:some_layout) { some_layout_class.new }
+
+          before { env.layout = some_layout }
+
+          it 'returns the assigned layout' do
+            expect(env.layout).to be some_layout
+          end
+        end
+
+        context 'when a layout class is set' do
+          before { env.layout_class = some_layout_class }
 
           it 'returns a new instance of this layout class' do
-            expect(env.layout).to be_an_instance_of some_layout
+            expect(env.layout).to be_an_instance_of some_layout_class
-          end
-        end
-
-        context 'when a layout class is not set' do
-          it 'returns an instance of the default layout' do
-            expect(env.layout).to be_an_instance_of ::Uh::Layout
           end
         end
       end

spec/uh/wm/run_control_spec.rb

@@ -85,6 +85,22 @@ module Uh
         end
       end
 
+      describe '#layout' do
+        context 'when given a class' do
+          it 'sets a layout class in the env' do
+            rc.layout layout_class = Class.new
+            expect(env.layout_class).to be layout_class
+          end
+        end
+
+        context 'when given an object' do
+          it 'sets a layout instance in the env' do
+            rc.layout layout = Object.new
+            expect(env.layout).to eq layout
+          end
+        end
+      end
+
       describe '#worker' do
         it 'sets the worker type in the env' do
           rc.worker :some_worker