Initialize include-files as Jekyll objects

lib/jekyll.rb

@@ -54,6 +54,7 @@ module Jekyll
   autoload :FrontmatterDefaults, "jekyll/frontmatter_defaults"
   autoload :Hooks,               "jekyll/hooks"
   autoload :Layout,              "jekyll/layout"
+  autoload :Inclusion,           "jekyll/inclusion"
   autoload :Cache,               "jekyll/cache"
   autoload :CollectionReader,    "jekyll/readers/collection_reader"
   autoload :DataReader,          "jekyll/readers/data_reader"

lib/jekyll/inclusion.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module Jekyll
+  class Inclusion
+    attr_reader :site, :name, :path
+    private :site
+
+    def initialize(site, base, name)
+      @site = site
+      @name = name
+      @path = PathManager.join(base, name)
+    end
+
+    def render(context)
+      @template ||= site.liquid_renderer.file(path).parse(content)
+      @template.render!(context)
+    rescue Liquid::Error => e
+      e.template_name  = path
+      e.markup_context = "included " if e.markup_context.nil?
+      raise e
+    end
+
+    def content
+      @content ||= File.read(path, **site.file_read_opts)
+    end
+
+    def inspect
+      "#{self.class} #{path.inspect}"
+    end
+    alias_method :to_s, :inspect
+  end
+end

lib/jekyll/site.rb

@@ -3,7 +3,7 @@
 module Jekyll
   class Site
     attr_reader   :source, :dest, :cache_dir, :config
-    attr_accessor :layouts, :pages, :static_files, :drafts,
+    attr_accessor :layouts, :pages, :static_files, :drafts, :inclusions,
                   :exclude, :include, :lsi, :highlighter, :permalink_style,
                   :time, :future, :unpublished, :safe, :plugins, :limit_posts,
                   :show_drafts, :keep_files, :baseurl, :data, :file_read_opts,
@@ -84,6 +84,7 @@ def print_stats
       Jekyll.logger.info @liquid_renderer.stats_table
     end
 
+    # rubocop:disable Metrics/AbcSize
     # rubocop:disable Metrics/MethodLength
     #
     # Reset Site details.
@@ -96,6 +97,7 @@ def reset
                     Time.now
                   end
       self.layouts = {}
+      self.inclusions = {}
       self.pages = []
       self.static_files = []
       self.data = {}
@@ -115,6 +117,7 @@ def reset
       Jekyll::Hooks.trigger :site, :after_reset, self
     end
     # rubocop:enable Metrics/MethodLength
+    # rubocop:enable Metrics/AbcSize
 
     # Load necessary libraries, plugins, converters, and generators.
     #

lib/jekyll/tags/include.rb

@@ -18,12 +18,13 @@ class IncludeTag < Liquid::Tag
 
       def initialize(tag_name, markup, tokens)
         super
-        matched = markup.strip.match(VARIABLE_SYNTAX)
+        markup  = markup.strip
+        matched = markup.match(VARIABLE_SYNTAX)
         if matched
           @file = matched["variable"].strip
           @params = matched["params"].strip
         else
-          @file, @params = markup.strip.split(%r!\s+!, 2)
+          @file, @params = markup.split(%r!\s+!, 2)
         end
         validate_params if @params
         @tag_name = tag_name
@@ -192,6 +193,60 @@ def could_not_locate_message(file, includes_dirs, safe)
       end
     end
 
+    # Do not inherit from this class.
+    # TODO: Merge into the `Jekyll::Tags::IncludeTag` in v5.0
+    class OptimizedIncludeTag < IncludeTag
+      def render(context)
+        @site ||= context.registers[:site]
+
+        file = render_variable(context) || @file
+        validate_file_name(file)
+
+        @site.inclusions[file] ||= locate_include_file(file)
+        inclusion = @site.inclusions[file]
+
+        add_include_to_dependency(inclusion, context) if @site.incremental?
+
+        context.stack do
+          context["include"] = parse_params(context) if @params
+          inclusion.render(context)
+        end
+      end
+
+      private
+
+      def locate_include_file(file)
+        @site.includes_load_paths.each do |dir|
+          path = PathManager.join(dir, file)
+          return Inclusion.new(@site, dir, file) if valid_include_file?(path, dir)
+        end
+        raise IOError, could_not_locate_message(file, @site.includes_load_paths, @site.safe)
+      end
+
+      def valid_include_file?(path, dir)
+        File.file?(path) && !outside_scope?(path, dir)
+      end
+
+      def outside_scope?(path, dir)
+        @site.safe && !realpath_prefixed_with?(path, dir)
+      end
+
+      def realpath_prefixed_with?(path, dir)
+        File.realpath(path).start_with?(dir)
+      rescue StandardError
+        false
+      end
+
+      def add_include_to_dependency(inclusion, context)
+        return unless context.registers[:page]&.key?("path")
+
+        @site.regenerator.add_dependency(
+          @site.in_source_dir(context.registers[:page]["path"]),
+          inclusion.path
+        )
+      end
+    end
+
     class IncludeRelativeTag < IncludeTag
       def tag_includes_dirs(context)
         Array(page_path(context)).freeze
@@ -217,5 +272,5 @@ def page_path(context)
   end
 end
 
-Liquid::Template.register_tag("include", Jekyll::Tags::IncludeTag)
+Liquid::Template.register_tag("include", Jekyll::Tags::OptimizedIncludeTag)
 Liquid::Template.register_tag("include_relative", Jekyll::Tags::IncludeRelativeTag)