When a directory gets added to extra-source-files, cabal sdist silently fails. Using strace revealed the error was due to a directory in the extra-source-files directive, but cabal itself didn't indicate any issue other than an exit code of 1.

It would be nice if mistakes like this could have an error message indicating roughly where and what to look for to get things working again.

Let me know if any other information is useful and I'll be sure to add it.

% cabal --version                                                                                                                                                             (git)-[develop] 
cabal-install version 2.0.0.0                                                                                                                                                                                                    
compiled using version 2.0.0.2 of the Cabal library

If anyone is willing to point me in the right direction, I'm more than happy to put forth an effort to work this issue myself as well.