Adding a debug log statment for skipped future posts.

For https://github.com/jekyll/jekyll/issues/4507

lib/jekyll/publisher.rb

@@ -8,14 +8,14 @@ module Jekyll
       can_be_published?(thing) && !hidden_in_the_future?(thing)
     end
 
+    def hidden_in_the_future?(thing)
+      thing.respond_to?(:date) && !@site.future && thing.date.to_i > @site.time.to_i
+    end
+
     private
 
     def can_be_published?(thing)
       thing.data.fetch('published', true) || @site.unpublished
     end
-
-    def hidden_in_the_future?(thing)
-      thing.respond_to?(:date) && !@site.future && thing.date.to_i > @site.time.to_i
-    end
   end
 end

lib/jekyll/readers/post_reader.rb

@@ -35,7 +35,11 @@ module Jekyll
       read_content(dir, magic_dir, matcher).tap do |docs|
         docs.each(&:read)
       end.select do |doc|
-        site.publisher.publish?(doc)
+        site.publisher.publish?(doc).tap do |will_publish|
+          if !will_publish && site.publisher.hidden_in_the_future?(doc)
+            Jekyll.logger.debug "Skipping:", "#{doc.relative_path} has a future date"
+          end
+        end
       end
     end