On Ubuntu 14.04 (ghc 7.6.3), "cabal install darcs-2.10.3" fails as
follows (after purging ~/.cabal), but it works with 2.10.2.

  Linking /tmp/darcs-2.10.3-10113/darcs-2.10.3/dist/setup/setup ...
  /usr/lib/ghc/unix-2.6.0.1/libHSunix-2.6.0.1.a(execvpe.o): In function `pPrPr_disableITimers':
  (.text+0x300): multiple definition of `pPrPr_disableITimers'
  /home/dlove/.cabal/lib/unix-2.7.1.0/ghc-7.6.3/libHSunix-2.7.1.0.a(ghcrts.o):ghcrts.c:(.text+0x0): first defined here
  collect2: error: ld returned 1 exit status
  Failed to install darcs-2.10.3
  cabal: Error: some packages failed to install:
  darcs-2.10.3 failed during the configure step. The exception was:
  ExitFailure 1

I don't know what other info might be relevant.

Thanks Dave,

I reproduced the bug on a machine with Ubuntu 14.04 (after deleting
.cabal and .ghc).

I found this, seems like we are not alone in the universe:

https://stackoverflow.com/questions/30687926/should-ghc-be-linking-different-versions-of-the-same-libraries

So, the useful piece of data here is that Darcs 2.10.2 compiles. Then
I guess a workaround for this problem would be to add some condition
on the GHC version in the darcs.cabal , something like:

if GHC < 7.10)
 then
    that-package < X
 else
    that-package < Y

(with X < Y)

But I haven't managed to make it work yet :-(

A cheap trick for the moment would be to compile the code of
darcs-2.10.3 with the darcs.cabal from darcs-2.10.2 .

Guillaume

Dave, did you also purge ~/.ghc ? That's where your installed 
packages would live that could be messing up your install.

I suspect that passing --constraint 'unix<2.7' , or using a sandbox 
(start with 'cabal sandbox init' in some throwaway directory) would 
also help. With cabal sandbox you would need to copy the resulting 
binary out of .cabal-sandbox/bin to somewhere on your PATH.

Sorry, I missed that Guillaume did try purging .ghc - that's quite 
surprising. Does a sandbox help for you?

Ganesh Sittampalam <bugs@darcs.net> writes:

> Ganesh Sittampalam <ganesh@earth.li> added the comment:
>
> Dave, did you also purge ~/.ghc ? That's where your installed 
> packages would live that could be messing up your install.

Yes, I did, sorry.

> I suspect that passing --constraint 'unix<2.7' ,

That produces

  cabal: The following packages are likely to be broken by the reinstalls:
  process-1.1.0.2
  haskell98-2.0.0.2
  ghc-7.6.3
  Cabal-1.16.0
  bin-package-db-0.0.0.0
  directory-1.2.0.1
  hpc-0.6.0.0
  Use --force-reinstalls if you want to install anyway.

> or using a sandbox 
> (start with 'cabal sandbox init' in some throwaway directory) would 
> also help. With cabal sandbox you would need to copy the resulting 
> binary out of .cabal-sandbox/bin to somewhere on your PATH.

cabal doesn't have a sandbox command.  I guess that means it's too old.
Sorry I don't know much about this stuff.

I'll try reverting to the old .cabal tomorrow.  Thanks.

I investigated if it was worth it asking Ubuntu people to backport a
new version of ghc so that Trusty (14.04) has unix 2.7.0.1 , but
apparently, it will *not* happen.

unix 2.7.0.1 appears only in Ubuntu Wily (15.04) with ghc 7.8 ( see
http://packages.ubuntu.com/wily/amd64/ghc/filelist ).

How about using stack to install a newer ghc in your working copy?

Guillaume Hoffmann <guillaumh@gmail.com> writes:

> I investigated if it was worth it asking Ubuntu people to backport a
> new version of ghc so that Trusty (14.04) has unix 2.7.0.1 , but
> apparently, it will *not* happen.
>
> unix 2.7.0.1 appears only in Ubuntu Wily (15.04) with ghc 7.8 ( see
> http://packages.ubuntu.com/wily/amd64/ghc/filelist ).
>
> How about using stack to install a newer ghc in your working copy?

Actually, it's not the compiler version.  The build works on Debian
stable, which has the same ghc 7.6.3.  I'll see if I can figure out what
the difference is from my limited knowledge of this stuff.

[I tried "cabal install stack", which couldn't resolve dependencies.]

On 08/02/2016 21:00, Dave Love wrote:
> 
> Ganesh Sittampalam <bugs@darcs.net> writes:
> 
> >> I suspect that passing --constraint 'unix<2.7' ,
> 
> That produces
> 
>   cabal: The following packages are likely to be broken by the reinstalls:
>   process-1.1.0.2
>   haskell98-2.0.0.2
>   ghc-7.6.3
>   Cabal-1.16.0
>   bin-package-db-0.0.0.0
>   directory-1.2.0.1
>   hpc-0.6.0.0
>   Use --force-reinstalls if you want to install anyway.

Hmm, that's strange. Can you provide the output of "ghc-pkg list" ?
Also, look at the version of "unix" it lists and pass that in a
constraint instead of 'unix<2.7', e.g. --constraint 'unix==2.6.0.1'. If
it lists multiple versions then pick the first.

If this still happens and you're not doing this as root, it should be
safe enough to try --force-reinstalls.

>> or using a sandbox 
>> (start with 'cabal sandbox init' in some throwaway directory) would 
>> also help. With cabal sandbox you would need to copy the resulting 
>> binary out of .cabal-sandbox/bin to somewhere on your PATH.

> cabal doesn't have a sandbox command.  I guess that means it's too old.
> Sorry I don't know much about this stuff.

You could try cabal install cabal-install to get a new one, but there's
always the risk that'll cause more hassle.I don't know if that wouldn't
have the same problem.

Cheers,

Ganesh

It turns out that "cabal install" in the unpacked 2.10.3 source
directory works.  It's just "cabal install darcs-2.10.3" that doesn't.