Prefer HEAD version if its installed

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index d6a536f5f..d9f110982 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -98,11 +98,20 @@ class Formula
 
   # if the dir is there, but it's empty we consider it not installed
   def installed?
-    return prefix.children.length > 0
+    return installed_prefix.children.length > 0
   rescue
     return false
   end
 
+  def installed_prefix
+    head_prefix = HOMEBREW_CELLAR+@name+'HEAD'
+    if @version == 'HEAD' || head_prefix.directory?
+      head_prefix
+    else
+      prefix
+    end
+  end
+
   def path
     self.class.path name
   end