cabal new-build: what does foo-setup~> mean?

[Ganesh Sittampalam]

Thanks: https://github.com/haskell/cabal/issues/4154

On 04/12/2016 18:55, Edward Z. Yang wrote:
> Hello Ganesh,
> 
> You should go ahead and file a bug on the Cabal tracker; the
> dep solver folks will be able to help you there.
> 
> ~> indicates "linking".  In the code comments:
> 
> -- The modular solver has a number of package goals to solve for, and can only
> -- pick a single package version for a single goal. In order to allow to
> -- install multiple versions of the same package as part of a single solution
> -- the solver uses qualified goals. For example, @0.P@ and @1.P@ might both
> -- be qualified goals for @P@, allowing to pick a difference version of package
> -- @P@ for @0.P@ and @1.P at .
> --
> -- Linking is an essential part of this story. In addition to picking a specific
> -- version for @1.P@, the solver can also decide to link @1.P@ to @0.P@ (or
> -- vice versa). It means that @1.P@ and @0.P@ really must be the very same package
> -- (and hence must have the same build time configuration, and their
> -- dependencies must also be the exact same).
> --
> -- See <http://www.well-typed.com/blog/2015/03/qualified-goals/> for details.
> 
> I haven't studied the actual error you have too closely.
> 
> Hope that helps,
> 
> Edward
> 
> Excerpts from Ganesh Sittampalam's message of 2016-12-03 18:45:24 +0000:
>> Hi,
>>
>> How should I interpret the following dependency solving error from cabal
>> new-build?
>>
>> Resolving dependencies...
>> cabal: Could not resolve dependencies:
>> trying: time-setup.time~>entropy-setup.time-1.1.2.3 (dependency of
>> time-1.1.2.3)
>> trying: time-setup.Cabal~>entropy-setup.Cabal-1.20.0.4 (dependency of
>> time-1.1.2.3)
>> Dependency tree exhaustively searched.
>>
>> FWIW I'm trying to build the HTTP package with GHC 7.0 and the following
>> options. The solver takes ~10 minutes before failing.
>>
>> --constraint 'time==1.1.2.3' --constraint 'entropy<0.2.2.4'
>> -f-warp-tests --constraint 'HUnit<1.4'
>>
>> cabal configure does seem to be able to find a solution.
>>
>> Cheers,
>>
>> Ganesh
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