Pacdiff

Simply type pacdiff -s and it will run sudoedit to merge the files. Use v to open vim with the pacnew file on the left, and the working file on the right with the focus on the pacnew file. Step through the changed hunks with ]c and then dp to push the chunk to the working file, or edit the working file as you want. Then exit from vim and type r to remove the pacnew. Sometimes I may pull changes to the pacnew with do (e.g. if you mostly want the pacnew version) and theno to overwrite with pacnew.

In case you're nervous about the overwrite, there's also -b, which before renaming your pacnew as the file, will rename your old file with ".bak" so you have your old version there in case you want to roll back easily