Make page excerpts consistent with doc excerpts

lib/jekyll/page.rb

@@ -49,6 +49,7 @@ def initialize(site, base, dir, name)
 
       process(name)
       read_yaml(PathManager.join(base, dir), name)
+      generate_excerpt if site.config["page_excerpts"]
 
       data.default_proc = proc do |_, key|
         site.frontmatter_defaults.find(relative_path, type, key)
@@ -185,14 +186,25 @@ def write?
     end
 
     def excerpt_separator
-      @excerpt_separator ||= data["excerpt_separator"] || site.config["excerpt_separator"] || ""
+      @excerpt_separator ||= (data["excerpt_separator"] || site.config["excerpt_separator"]).to_s
     end
 
     def excerpt
-      return if excerpt_separator.empty? || !site.config["page_excerpts"]
-      return data["excerpt"] unless self.class == Jekyll::Page && html?
+      return @excerpt if defined?(@excerpt)
 
-      data["excerpt"] ||= Jekyll::PageExcerpt.new(self).to_liquid
+      @excerpt = data["excerpt"]&.to_s
+    end
+
+    def generate_excerpt?
+      !excerpt_separator.empty? && self.class == Jekyll::Page && html?
+    end
+
+    private
+
+    def generate_excerpt
+      return unless generate_excerpt?
+
+      data["excerpt"] ||= Jekyll::PageExcerpt.new(self)
     end
   end
 end

lib/jekyll/page_excerpt.rb

@@ -2,15 +2,14 @@
 
 module Jekyll
   class PageExcerpt < Excerpt
-    attr_reader :output, :doc
+    attr_reader :doc
     alias_method :id, :relative_path
 
-    # The Liquid representation of this instance is simply the rendered output string.
-    alias_method :to_liquid, :output
+    EXCERPT_ATTRIBUTES = (Page::ATTRIBUTES_FOR_LIQUID - %w(excerpt)).freeze
+    private_constant :EXCERPT_ATTRIBUTES
 
-    def initialize(doc)
-      super
-      self.output = Renderer.new(site, self, site.site_payload).run
+    def to_liquid
+      @to_liquid ||= doc.to_liquid(EXCERPT_ATTRIBUTES)
     end
 
     def render_with_liquid?

test/source/assets/test-styles.scss

@@ -1,4 +1,4 @@
----
----
-
-@import "{{ site.skin | default: 'grid' }}";
+---
+---
+
+@import "{{ site.skin | default: 'grid' }}";

test/source/contacts/foo.md

@@ -0,0 +1,7 @@
+---
+title: Contact Information
+---
+
+## {{ page.title }}
+
+In case of emergency, contact Mr. John Doe, 1234, Foo Road, Foo.

test/test_filters.rb

@@ -816,7 +816,7 @@ def to_liquid
               "The list of grouped items for '' is not an Array."
             )
             # adjust array.size to ignore symlinked page in Windows
-            qty = Utils::Platforms.really_windows? ? 18 : 20
+            qty = Utils::Platforms.really_windows? ? 19 : 21
             assert_equal qty, g["items"].size
           end
         end
@@ -1310,7 +1310,7 @@ def to_liquid
               "The list of grouped items for '' is not an Array."
             )
             # adjust array.size to ignore symlinked page in Windows
-            qty = Utils::Platforms.really_windows? ? 18 : 20
+            qty = Utils::Platforms.really_windows? ? 19 : 21
             assert_equal qty, g["items"].size
           end
         end

test/test_page.rb

@@ -369,22 +369,39 @@ def do_render(page)
       end
 
       context "read-in by default" do
-        should "not expose an excerpt to Liquid templates" do
+        should "not initialize excerpts by default" do
+          page = setup_page("contacts", "foo.md")
+          assert_nil page.excerpt
+        end
+
+        should "not expose an excerpt to Liquid templates by default" do
           page = setup_page("/contacts", "bar.html")
           assert_nil page.to_liquid["excerpt"]
         end
 
-        should "expose an excerpt to Liquid templates if site is configured to" do
-          configured_site = fixture_site("page_excerpts" => true)
-          test_page = Jekyll::Page.new(configured_site, source_dir, "/contacts", "bar.html")
-          assert_equal "Contact Information\n", test_page.to_liquid["excerpt"]
-        end
+        context "in a site configured to generate page excerpts" do
+          setup { @configured_site = fixture_site("page_excerpts" => true) }
+
+          should "initialize excerpt eagerly but render only when needed" do
+            test_page = Jekyll::Page.new(@configured_site, source_dir, "contacts", "foo.md")
+            assert_equal Jekyll::PageExcerpt, test_page.data["excerpt"].class
+            assert_equal String, test_page.excerpt.class
+            assert_equal(
+              "<h2 id=\"contact-information\">Contact Information</h2>\n",
+              test_page.excerpt
+            )
+          end
+
+          should "expose an excerpt to Liquid templates" do
+            test_page = Jekyll::Page.new(@configured_site, source_dir, "/contacts", "bar.html")
+            assert_equal "Contact Information\n", test_page.to_liquid["excerpt"]
+          end
 
-        should "not expose an excerpt for non-html pages even in a configured site" do
-          configured_site = fixture_site("page_excerpts" => true)
-          test_page = Jekyll::Page.new(configured_site, source_dir, "assets", "test-styles.scss")
-          refute_equal ".half { width: 50%; }\n", test_page.to_liquid["excerpt"]
-          assert_nil test_page.to_liquid["excerpt"]
+          should "not expose an excerpt for non-html pages" do
+            test_page = Jekyll::Page.new(@configured_site, source_dir, "assets", "test-styles.scss")
+            refute_equal ".half { width: 50%; }\n", test_page.to_liquid["excerpt"]
+            assert_nil test_page.to_liquid["excerpt"]
+          end
         end
       end
 

test/test_site.rb

@@ -232,6 +232,7 @@ def generate(site)
         environment.html
         exploit.md
         foo.md
+        foo.md
         humans.txt
         index.html
         index.html