Perhaps "Failure when adding dependencies" error output could be less noisy

[radix]

While I'm converting large projects that have lots of dependencies to stack, I often end up looking at screens like this (and this is actually one of the shorter examples):

--  Failure when adding dependencies:    
      network: needed (==2.6.*), 2.5.0.0 found (latest applicable is 2.6.2.1)
    needed for package: HTTP-4000.2.20

--  Failure when adding dependencies:    
      HTTP: needed (-any), couldn't resolve its dependencies
      http-client: needed (-any), couldn't resolve its dependencies
      http-client-tls: needed (-any), couldn't resolve its dependencies
      http-conduit: needed (-any), couldn't resolve its dependencies
      webdriver: needed (-any), couldn't resolve its dependencies
    needed for package: backend-0.1

--  Failure when adding dependencies:    
      network: needed (>=2.6), 2.5.0.0 found (latest applicable is 2.6.2.1)
    needed for package: http-client-0.4.3

--  Failure when adding dependencies:    
      http-client: needed (>=0.3.5), couldn't resolve its dependencies
    needed for package: http-client-tls-0.2.2

--  Failure when adding dependencies:    
      http-client: needed (>=0.4.3 && <0.4.19), couldn't resolve its dependencies
      http-client-tls: needed (>=0.2.2), couldn't resolve its dependencies
    needed for package: http-conduit-2.1.7.2

--  Failure when adding dependencies:    
      http-client: needed (>=0.3 && <0.5), couldn't resolve its dependencies
      network: needed (>=2.6), 2.5.0.0 found (latest applicable is 2.6.2.1)
    needed for package: webdriver-0.6.2

If you look closely, there are basically two interesting pieces of information in this error output:

      network: needed (==2.6.*), 2.5.0.0 found (latest applicable is 2.6.2.1)
    needed for package: HTTP-4000.2.20

and

      network: needed (>=2.6), 2.5.0.0 found (latest applicable is 2.6.2.1)
    needed for package: http-client-0.4.3

All the rest of the errors are just downstream of those packages that have this version conflict. So, perhaps they could be elided (or made much more terse) when we know that the only problems with a package is that it depends on another package that we're already reporting errors for.

[sjakobi]

Improvements to the error output are already being discussed in #713.

If you have any ideas on how to make these error messages less terse and more helpful, I'd be really interested! :)

[sjakobi]

I just found #1739, of which this issues is pretty much a duplicate. Let's move the discussion there.