ghc --make on Haskell and non-Haskell inputs can silently clobber input
Create any valid files A.hs and A.c, then run
ghc --make A.hs A.c. You'll get one
A.o file for
A.c is lost to the sands of time.
I thought this situation would be pretty unlikely but geekosaur mentioned to me that he had seen someone run into this problem before.