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

[Edward Z. Yang]

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