Maybe there’s something to the cult-of-git after all 
. vcl/unx/source/fontmanager/fontcache.cxx had some code which painstakingly constructed a string, only to do nothing with it. Clearly at some time in the past it was used, so when did its use go away. This is a file which has been moved around over the years from place to place, hmm, potentially tricky to scratch the itch of knowing when it happened ?, not at all…
git log --follow --oneline -S'suspiciously missing variable' /path/to/file.cxx
and 2 seconds later I have a list of 5 commits, there it is at the top of the list. Back in 2005, a rework of the font cache where the stat on a file was optimized out, while the constructed path to the file remained. No undetected nightmare merge bug then, just a missed micro optimization opportunity.