brew-unpack: Handle new style :DATA patches

Instances of `IOPatch` created by `patch :DATA` are not affected by re-setting
the `DATA` constant of the `Formula` instance. For these patches, we iterate
through the `patchlist` and use `instance_variable_set` to attach data.

A bit hacky, but `patchlist` has no write accessors so there isn't a clean way
to modify patch contents.

Library/Contributions/cmd/brew-unpack.rb

@@ -28,6 +28,7 @@ module UnpackPatch
     return unless ARGV.flag? "--patch"
 
     begin
+      # Silence complaints about re-setting constants.
       old_verbose = $VERBOSE
       $VERBOSE = nil
       Formula.const_set "DATA", ScriptDataReader.load(path)
@@ -35,6 +36,14 @@ module UnpackPatch
       $VERBOSE = old_verbose
     end
 
+    # Legacy patches are fixed by setting Formula::DATA.
+    # Now, handle instances of IOPatch.
+    patchlist.select{|p| p.is_a? IOPatch}.each do |patch|
+      if patch.instance_variable_get(:@io) == :DATA
+        patch.instance_variable_set :@io, ScriptDataReader.load(path)
+      end
+    end
+
     super
   end
 end