Better output for parallel install.

[23Skidoo]

Example of what happens in the normal case: https://gist.github.com/3032723
Example of what happens in case of error: https://gist.github.com/3032939

[tibbe]

Could you please add some comments to your code, especially to the part that overrides the logging verbosity (e.g. taking the max of two verbosities etc.)

[tibbe]

@dcoutts Could you please have a look at this change to make sure we're doing the right things to suppress build output in the case of parallell builds?

[23Skidoo]

Added some comments.

(e.g. taking the max of two verbosities etc.)

This is just code reorganization. When the user has specified --build-log=PATH or --remote-build-reporting=detailed, logging should be more verbose.

[dcoutts]

The output is certainly nicer. Code looks ok too. I'm happy for this to be merged.

One further improvement might be to do something about the:

cabal: Error: some packages failed to install:
Win32-2.2.2.0 failed during the configure step. The exception was:
ExitFailure 1

If we could combine this with the nice thing about printing the last 10 lines that'd be ideal. Printing the exception is pretty useless where as the last 10 lines of the build log are pretty good, plus the file name if you want to look further. The difficulty with making a further change here is what to do in the normal case when we're doing a normal build logged to the console. In that case we don't collect the log so we would not be able to print the last 10 lines. I think the solution here would be to improve Cabal's process utils so that we can run a program and both log the output to a file and display it live on screen, like the unix tee utility.

[23Skidoo]

Regarding the exception, this is no worse than the current output in the serial case. In the future, I want to implement a dynamically-updated status indicator, like described in the original ticket (#440). We can use it both in the serial and in the parallel case, which will make the code simpler.

[tibbe]

@23Skidoo Let me know if you want me to merge this as-is or if you want to do any of Duncan's suggested changes now.

[23Skidoo]

I'd like to merge this change right now; at some later point in the future I'll implement a dynamic status indicator (which will subsume Duncan's suggestion).