Don't generate excerpts for non-html pages

lib/jekyll/page.rb

@@ -190,7 +190,7 @@ def excerpt_separator
 
     def excerpt
       return if excerpt_separator.empty? || !site.config["page_excerpts"]
-      return data["excerpt"] unless self.class == Jekyll::Page
+      return data["excerpt"] unless self.class == Jekyll::Page && html?
 
       data["excerpt"] ||= Jekyll::PageExcerpt.new(self).to_liquid
     end

test/source/assets/test-styles.scss

@@ -0,0 +1,4 @@
+---
+---
+
+@import "{{ site.skin | default: 'grid' }}";

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? ? 16 : 18
+            qty = Utils::Platforms.really_windows? ? 18 : 20
             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? ? 16 : 18
+            qty = Utils::Platforms.really_windows? ? 18 : 20
             assert_equal qty, g["items"].size
           end
         end

test/test_page.rb

@@ -379,6 +379,13 @@ def do_render(page)
           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"]
+        end
       end
 
       context "generated via plugin" do

test/test_site.rb

@@ -241,6 +241,8 @@ def generate(site)
         properties.html
         sitemap.xml
         static_files.html
+        test-styles.css.map
+        test-styles.scss
         trailing-dots...md
       )
       unless Utils::Platforms.really_windows?