Don't reset site.url to localhost:4000 by default (#7253)

Merge pull request 7253

lib/jekyll/commands/serve.rb

@@ -249,6 +249,9 @@ module Jekyll
 
         def default_url(opts)
           config = configuration_from_options(opts)
+          auth = config.values_at("host", "port").join(":")
+          return config["url"] if auth == "127.0.0.1:4000"
+
           format_url(
             config["ssl_cert"] && config["ssl_key"],
             config["host"] == "127.0.0.1" ? "localhost" : config["host"],

test/test_commands_serve.rb

@@ -232,12 +232,6 @@ class TestCommandsServe < JekyllUnitTest
           expect(Jekyll).to receive(:env).and_return("development")
           expect(Jekyll::Commands::Serve).to receive(:start_up_webrick)
         end
-        should "set the site url by default to `http://localhost:4000`" do
-          @merc.execute(:serve, "watch" => false, "url" => "https://jekyllrb.com/")
-
-          assert_equal 1, Jekyll.sites.count
-          assert_equal "http://localhost:4000", Jekyll.sites.first.config["url"]
-        end
 
         should "take `host`, `port` and `ssl` into consideration if set" do
           @merc.execute(:serve,