[Haskell-cafe] circular dependencies in cabal

[Valentyn Kamyshenko]

So, in practical terms, you suggest that no new version of the package  
that ghc package depends on (directly or indirectly) should ever be  
installed?
For example, as soon as process-1.0.1.1 is installed on my computer,  
I'll have this problem with every package that depends on "process"?
Another question: would not cabal-install automatically fetch the most  
recent version of the "process" package, as soon as I will try to  
install
a package that depends on it (such as, for example, "plugins")?

-- Valentyn.

On Feb 1, 2009, at 6:53 AM, Duncan Coutts wrote:

> On Sun, 2009-02-01 at 01:33 -0800, Valentyn Kamyshenko wrote:
>> Hello all,
>>
>> when I tried to install plugins package with cabal, I've got the
>> following error:
>>
>> # sudo cabal install plugins --global
>> Resolving dependencies...
>> cabal: dependencies conflict: ghc-6.10.1 requires process ==1.0.1.1
>> however
>> process-1.0.1.1 was excluded because ghc-6.10.1 requires process
>> ==1.0.1.0
>
> For the most part I refer you to:
>
> http://haskell.org/pipermail/haskell-cafe/2009-January/054523.html
>
> However the difference is that you've got this problem only within the
> global package db rather than due to overlap in the global and user
> package db.
>
>> It looks like both versions of process package are currently  
>> required:
>
> It looks like you installed process-1.0.1.1 and then rebuilt almost
> every other package against it. Of course you cannot rebuild the ghc
> package but you did rebuild some of its dependencies which is why it  
> now
> depends on multiple versions of the process package.
>
> Generally rebuilding a package without also rebuilding the packages  
> that
> depend on it is a bit dodgy (it can lead to linker errors or  
> segfaults).
> Unfortunately cabal-install does not prevent you from shooting  
> yourself
> in the foot in these circumstances.
>
>> Any suggestions?
>
> Aim for a situation where you only have one version of the various  
> core
> packages. If you do not need to install packages globally then
> installing them per-user means you at least cannot break the global
> packages.
>
> Duncan
>