"GHC creates a subdirectory .hpc in the current directory, and puts HPC index (.mix) files in there..." https://www.haskell.org/ghc/docs/7.4.2/html/users_guide/hpc.html
@@ -5,6 +5,7 @@ cabal-dev
*.chi
*.chs.h
.virtualenv
+.hpc
.hsenv
.cabal-sandbox/
cabal.sandbox.config
Michael LaCorte