More helpful error-message than "The exception was: ExitFailure 1"

[k-bx]

Hi!

This is a proposal to make life little easier for beginners. I don't know how much work this would require, wanted to discuss possible solutions before looking into.

Currently, it's very common to see error like this when compilation fails:

somepackage-4.0 failed during the building phase. The exception was:
ExitFailure 1

I just figured out that I was so used to it that almost thought of it as a "normal thing". But it isn't, and I'd like to discuss possible enhancements to this, especially from people who are familiar with cabal's code-base.

[ygale]

There many situations where this happens. Generally, it means that some other program called by cabal during the build process failed. So you are supposed to look further up in the output to find the true error message.

It would be great if cabal would report which program failed and at what point in the build process. And then instruct the user how to find out what when wrong in a friendlier way. Best would be to capture the actual error message and repeat it at the end together with a clear explanation of the context, but that might be hard to do reliably.

[bitemyapp]

@k-bx Often I find this happens because a secondary command failed (cpp, ld, etc.) or because the linker got OOM-killed. You have to trawl the logs to find out for sure. If there's an abrupt stop in the logs, I'd grep /var/log/messages for killed process to see if the OOM killer is responsible.

[k-bx]

@bitemyapp @ygale so I wonder would it be better for a newbie to see something like:

somepackage-4.0 failed during the building phase. Failed command was:

    cabal install something<1

Please, see previous debug output for more information.

[bitemyapp]

@k-bx something like that could definitely help, currently you have to scroll up to find the error.

[ntc2]

This issue is a duplicate of #1152, although I think think this issue has a better title because it mentions ExitFailure.

(EDIT: fix link)