Add HEAD information to JSON API

Library/Homebrew/formula.rb

@@ -2139,6 +2139,13 @@ class Formula
       hsh["bottle"]["stable"] = bottle_hash if bottle_defined?
     end
 
+    if head
+      hsh["urls"]["head"] = {
+        "url"    => head.url,
+        "branch" => head.specs[:branch],
+      }
+    end
+
     hsh["options"] = options.map do |opt|
       { "option" => opt.flag, "description" => opt.description }
     end

Library/Homebrew/formulary.rb

@@ -163,6 +163,10 @@ module Formulary
         end
       end
 
+      if (urls_head = json_formula["urls"]["head"]).present?
+        head urls_head["url"], branch: urls_head["branch"]
+      end
+
       if (bottles_stable = json_formula["bottle"]["stable"]).present?
         bottle do
           root_url bottles_stable["root_url"]