Add PageWithoutAFile class from jekyll plugins (#6556)

Merge pull request 6556

lib/jekyll.rb

@@ -61,6 +61,7 @@ module Jekyll
   autoload :ThemeAssetsReader,   "jekyll/readers/theme_assets_reader"
   autoload :LogAdapter,          "jekyll/log_adapter"
   autoload :Page,                "jekyll/page"
+  autoload :PageWithoutAFile,    "jekyll/page_without_a_file"
   autoload :PluginManager,       "jekyll/plugin_manager"
   autoload :Publisher,           "jekyll/publisher"
   autoload :Reader,              "jekyll/reader"

lib/jekyll/page_without_a_file.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module Jekyll
+  # A Jekyll::Page subclass to handle processing files without reading it to
+  # determine the page-data and page-content based on Front Matter delimiters.
+  #
+  # The class instance is basically just a bare-bones entity with just
+  # attributes "dir", "name", "path", "url" defined on it.
+  class PageWithoutAFile < Page
+    def read_yaml(*)
+      @data ||= {}
+    end
+
+    def inspect
+      "#<Jekyll:PageWithoutAFile @name=#{name.inspect}>"
+    end
+  end
+end