Support nested Kits (#840)

With this change, Kits will now propagate down to nested modules. There
is currently no way to disable this behaviour, but if anyone needs that,
the plan is to introduce `BasicKit` which will not propagate.

fixtures/components.rb

@@ -5,4 +5,12 @@ module Components
 
 	autoload :SayHi, "components/say_hi"
 	autoload :Article, "components/article"
+
+	module Foo
+		class Bar < Phlex::HTML
+			def view_template
+				h1 { "Bar" }
+			end
+		end
+	end
 end

lib/phlex/kit.rb

@@ -49,27 +49,32 @@ def const_added(name)
 		me = self
 		constant = const_get(name)
 
-		if Class === constant && constant < Phlex::SGML
-			constant.include(self)
+		case constant
+		when Class
+			if constant < Phlex::SGML
+				constant.include(self)
 
-			constant = nil
+				constant = nil
 
-			define_method(name) do |*args, **kwargs, &block|
-				constant = me.const_get(name)
-				render(constant.new(*args, **kwargs), &block)
-			end
+				define_method(name) do |*args, **kwargs, &block|
+					constant = me.const_get(name)
+					render(constant.new(*args, **kwargs), &block)
+				end
 
-			define_singleton_method(name) do |*args, **kwargs, &block|
-				component, fiber_id = Thread.current[:__phlex_component__]
-				if (component && fiber_id == Fiber.current.object_id)
-					component.instance_exec do
-						constant = me.const_get(name)
-						render(constant.new(*args, **kwargs), &block)
+				define_singleton_method(name) do |*args, **kwargs, &block|
+					component, fiber_id = Thread.current[:__phlex_component__]
+					if (component && fiber_id == Fiber.current.object_id)
+						component.instance_exec do
+							constant = me.const_get(name)
+							render(constant.new(*args, **kwargs), &block)
+						end
+					else
+						raise "You can't call `#{name}' outside of a Phlex rendering context."
 					end
-				else
-					raise "You can't call `#{name}' outside of a Phlex rendering context."
 				end
 			end
+		when Module
+			constant.extend(Phlex::Kit)
 		end
 
 		super

quickdraw/kit.test.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 require "components"
+require "sgml_helper"
+include SGMLHelper
 
 class Example < Phlex::HTML
 	include Components
@@ -19,3 +21,7 @@ def view_template
 test "defines methods for its components" do
 	assert_equal Example.new.call, %(<article><h1>Hi Joel</h1><h1>Hi Joel</h1>Inside</article><article><h1>Hi Will</h1>Inside</article>)
 end
+
+test "nested kits" do
+	assert_equal_html phlex { Components::Foo::Bar() }, "<h1>Bar</h1>"
+end