Inconsistent travis results with cabal-1.22 and ghc-7.10.3

[mgsloan]

Sorry if this is just noise, but I have no idea what is happening here: commercialhaskell/stack#2121

The strange thing is that this started occuring spontaneously, as far as I can tell not due to any changes to our travis config. Perhaps there are issues with older versions of cabal that cause corrupted packages / missing dbs?

[23Skidoo]

To summarise: you got your Travis .ghc/.cabal borked somehow, which was fixed by clearing the Travis cache. But then the build started failing because mtl failed to install with the following error:

Failed to install mtl-2.2.1
Build log ( /home/travis/.cabal/logs/mtl-2.2.1.log ):
Configuring mtl-2.2.1...
Building mtl-2.2.1...
Preprocessing library mtl-2.2.1...
/home/travis/.ghc/x86_64-linux-7.10.2/package.conf.d/package.cache: openBinaryFile: does not exist (No such file or directory)

I believe that the error comes from ghc or ghc-pkg since Cabal never reads stuff in .ghc directly. I'd try adding a call to ghc-pkg recache to your script before the cabal install invocation and see if it fixes the error.

[23Skidoo]

One possibility is that there's a race condition in parallel install when one process updates package.cache and another tries to read from it. It may be possible to fix it in ghc-pkg: e.g., this fragment looks suspicious.

[23Skidoo]

You can also try running cabal install -v2 or -v3 and looking at the logs.

[jneira]

those version are really old and this issue is somewhat obsolete
@mgsloan feel free to reopen if you continue experiencing the bug with newer versions