Parse raw diff output in `brew update`

Using each_cons() "works", but to report all changes correctly we need
to look at the last elements even after we've looked at the last 3
consecutive elements.

Instead, let's parse each line of the raw diff output using a regexp.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Library/Homebrew/cmd/update.rb

@@ -80,19 +80,21 @@ class Updater
     @current_revision = read_current_revision
   end
 
+  # Matches raw git diff format (see `man git-diff-tree`)
+  DIFFTREE_RX = /^:[0-7]{6} [0-7]{6} [0-9a-fA-F]{40} [0-9a-fA-F]{40} ([ACDMR])\d{0,3}\t(.+?)(?:\t(.+))?$/
+
   def report
     map = Hash.new{ |h,k| h[k] = [] }
 
     if initial_revision && initial_revision != current_revision
-      changes = `git diff-tree -r --name-status -M85% -z #{initial_revision} #{current_revision}`.split("\0")
-      changes.each_cons(3) do |status, src, dst|
-        next unless status =~ /^[AMDR](\d{3})?$/
-        path = case status = status[0,1]
-          when 'R' then dst
-          else src
+      `git diff-tree -r --raw -M85% #{initial_revision} #{current_revision}`.each_line do |line|
+        DIFFTREE_RX.match line
+        path = case status = $1.to_sym
+          when :R then $3
+          else $2
           end
         path = Pathname.pwd.join(path).relative_path_from(HOMEBREW_REPOSITORY)
-        map[status.to_sym] << path.to_s
+        map[status] << path.to_s
       end
     end