Add URL checks to Doctor

lib/jekyll/commands/doctor.rb

@@ -1,3 +1,5 @@
+require "addressable/uri"
+
 module Jekyll
   module Commands
     class Doctor < Command
@@ -35,7 +37,8 @@ def healthy?(site)
             fsnotify_buggy?(site),
             !deprecated_relative_permalinks(site),
             !conflicting_urls(site),
-            !urls_only_differ_by_case(site)
+            !urls_only_differ_by_case(site),
+            proper_site_url?(site)
           ].all?
         end
 
@@ -91,6 +94,13 @@ def urls_only_differ_by_case(site)
           urls_only_differ_by_case
         end
 
+        def proper_site_url?(site)
+          url = site.config["url"]
+          url_exists?(url) &&
+            url_valid?(url) &&
+            url_absolute(url)
+        end
+
         private
         def collect_urls(urls, things, destination)
           things.each do |thing|
@@ -110,6 +120,27 @@ def case_insensitive_urls(things, destination)
             (memo[dest.downcase] ||= []) << dest
           end
         end
+
+        def url_exists?(url)
+          return true unless url.nil? || url.empty?
+          Jekyll.logger.warn "Warning:", "Site URL does not appear to be set"
+          false
+        end
+
+        def url_valid?(url)
+          Addressable::URI.parse(url)
+          true
+        rescue
+          Jekyll.logger.warn "Warning:", "Cannot parse site URL: #{url}"
+          false
+        end
+
+        def url_absolute(url)
+          return true if Addressable::URI.parse(url).absolute?
+          Jekyll.logger.warn "Warning:", "Site URL does not appear to be" \
+            " absolute: #{url}"
+          false
+        end
       end
     end
   end