Revert #7253: "Don't reset site.url to localhost:4000 by default"

docs/_docs/usage.md

@@ -23,8 +23,8 @@ Here are some of the most common commands:
 
 * `jekyll new PATH` - Creates a new Jekyll site with default gem-based theme at specified path. The directories will be created as necessary.
 * `jekyll new PATH --blank` - Creates a new blank Jekyll site scaffold at specified path.
-* `jekyll build` or `jekyll b` - Performs a one off build your site to `./_site` (by default).
-* `jekyll serve` or `jekyll s` - Builds your site any time a source file changes and serves it locally.
+* `jekyll build` or `jekyll b` - Performs a one off build your site to `./_site`, using the production configuration (by default).
+* `jekyll serve` or `jekyll s` - Builds your site any time a source file changes and serves it locally, using placeholders for the site URLs to enable it to be served locally (by default). Should not be used to generate a site copy that will be deployed to a live website.
 * `jekyll clean` - Removes all generated files: destination folder, metadata file, Sass and Jekyll caches.
 * `jekyll help` - Shows help, optionally for a given subcommand, e.g. `jekyll help build`.
 * `jekyll new-theme` - Creates a new Jekyll theme scaffold.

lib/jekyll/commands/serve.rb

@@ -249,9 +249,6 @@ def format_url(ssl_enabled, address, port, baseurl = nil)
 
         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

@@ -232,6 +232,12 @@ def serve(opts)
           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,