Make rails configuration's path object's root lazy

railties/lib/rails/paths.rb

@@ -19,14 +19,15 @@ module Rails
     class Root
       include PathParent
 
-      attr_reader :path
+      attr_accessor :path
+
       def initialize(path)
-        raise unless path.is_a?(String)
+        raise if path.is_a?(Array)
 
         @children = {}
 
         # TODO: Move logic from set_root_path initializer
-        @path = File.expand_path(path)
+        @path = path
         @root = self
         @all_paths = []
       end
@@ -123,8 +124,10 @@ module Rails
       end
 
       def paths
+        raise "You need to set a path root" unless @root.path
+
         @paths.map do |path|
-          path.index('/') == 0 ? path : File.join(@root.path, path)
+          path.index('/') == 0 ? path : File.expand_path(File.join(@root.path, path))
         end
       end
 

railties/test/paths_test.rb

@@ -12,11 +12,32 @@ class PathsTest < ActiveSupport::TestCase
     assert_equal "/fiz/baz", root.path
   end
 
+  test "the paths object can be initialized with nil" do
+    assert_nothing_raised do
+      Rails::Application::Root.new(nil)
+    end
+  end
+
+  test "a paths object initialized with nil can be updated" do
+    root = Rails::Application::Root.new(nil)
+    root.app = "app"
+    root.path = "/root"
+    assert_equal ["/root/app"], root.app.to_a
+  end
+
   test "creating a root level path" do
     @root.app = "/foo/bar"
     assert_equal ["/foo/bar"], @root.app.to_a
   end
 
+  test "raises exception if root path never set" do
+    root = Rails::Application::Root.new(nil)
+    root.app = "app"
+    assert_raises RuntimeError do
+      root.app.to_a
+    end
+  end
+
   test "creating a root level path without assignment" do
     @root.app "/foo/bar"
     assert_equal ["/foo/bar"], @root.app.to_a