Allow excerpts to be generated for Page objects (#7642)

Merge pull request 7642

lib/jekyll.rb

@@ -50,6 +50,7 @@ module Jekyll
   autoload :EntryFilter,         "jekyll/entry_filter"
   autoload :Errors,              "jekyll/errors"
   autoload :Excerpt,             "jekyll/excerpt"
+  autoload :PageExcerpt,         "jekyll/page_excerpt"
   autoload :External,            "jekyll/external"
   autoload :FrontmatterDefaults, "jekyll/frontmatter_defaults"
   autoload :Hooks,               "jekyll/hooks"

lib/jekyll/drops/page_drop.rb

@@ -7,7 +7,7 @@ module Jekyll
 
       mutable false
 
-      def_delegators :@obj, :content, :dir, :name, :path, :url
+      def_delegators :@obj, :content, :dir, :name, :path, :url, :excerpt
       private def_delegator :@obj, :data, :fallback_data
 
       def title

lib/jekyll/page.rb

@@ -15,6 +15,7 @@ module Jekyll
     ATTRIBUTES_FOR_LIQUID = %w(
       content
       dir
+      excerpt
       name
       path
       url
@@ -214,5 +215,15 @@ module Jekyll
     def write?
       true
     end
+
+    def excerpt_separator
+      @excerpt_separator ||= (data["excerpt_separator"] || site.config["excerpt_separator"]).to_s
+    end
+
+    def excerpt
+      return data["excerpt"] unless self.class == Jekyll::Page
+
+      data["excerpt"] ||= Jekyll::PageExcerpt.new(self).to_liquid unless excerpt_separator.empty?
+    end
   end
 end

lib/jekyll/page_excerpt.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+module Jekyll
+  class PageExcerpt < Excerpt
+    attr_reader :output, :doc
+    alias_method :id, :relative_path
+
+    # The Liquid representation of this instance is simply the rendered output string.
+    alias_method :to_liquid, :output
+
+    def initialize(doc)
+      super
+      self.output = Renderer.new(site, self, site.site_payload).run
+    end
+
+    def render_with_liquid?
+      return false if data["render_with_liquid"] == false
+
+      Jekyll::Utils.has_liquid_construct?(content)
+    end
+
+    def inspect
+      "#<#{self.class} id=#{id.inspect}>"
+    end
+  end
+end

test/test_page.rb

@@ -125,7 +125,7 @@ class TestPage < JekyllUnitTest
         attrs = {
           :content   => "All the properties.\n",
           :dir       => "/properties/",
-          :excerpt   => nil,
+          :excerpt   => "All the properties.\n",
           :foo       => "bar",
           :layout    => "default",
           :name      => "properties.html",
@@ -403,6 +403,32 @@ class TestPage < JekyllUnitTest
           assert_exist dest_dir("contacts", "bar", "index.html")
         end
       end
+
+      context "read-in by default" do
+        should "expose an excerpt to Liquid templates" do
+          page = setup_page("/contacts", "bar.html")
+          assert_equal "Contact Information\n", page.to_liquid["excerpt"]
+        end
+      end
+
+      context "generated via plugin" do
+        setup do
+          PageSubclass = Class.new(Jekyll::Page)
+          @test_page = PageSubclass.new(@site, source_dir, "/contacts", "bar.html")
+          @test_page.data.clear
+        end
+
+        should "not expose an excerpt to Liquid templates by default" do
+          assert_equal "Contact Information\n", @test_page.content
+          assert_nil @test_page.to_liquid["excerpt"]
+        end
+
+        should "expose an excerpt to Liquid templates if hardcoded" do
+          @test_page.data["excerpt"] = "Test excerpt."
+          assert_equal "Contact Information\n", @test_page.content
+          assert_equal "Test excerpt.", @test_page.to_liquid["excerpt"]
+        end
+      end
     end
   end
 end

test/test_page_without_a_file.rb

@@ -49,9 +49,9 @@ class TestPageWithoutAFile < JekyllUnitTest
         assert_equal "All the properties.\n", regular_page["content"]
         assert_equal "properties.html", regular_page["name"]
 
-        basic_attrs = %w(dir name path url)
+        basic_attrs = %w(dir name path url excerpt)
         attrs = {
-          "content"   => "All the properties.\n",
+          "content"   => nil,
           "dir"       => "/",
           "excerpt"   => nil,
           "foo"       => "bar",