HEADS UP: Running cabal install with the latest GHC

[Edward Z. Yang]

They would be:

    2b50d0a Fix regression for V09 test library handling.
    d3a696a Disable reinstalls with distinct package keys for now.
    1d33c8f Add $pkgkey template variable, and use it for install paths.
    41610a0 Implement package keys, distinguishing packages built with different deps/flags

Unfortunately, these patches fuzz a bit without this next patch:

    62450f9 Implement "reexported-modules" field, towards fixing GHC bug #8407.

When you include that patch, there is only one piece of fuzz from
41610a0.

One important caveat is that these patches do rearrange some of the API,
so you wouldn't be able to build GHC 7.8 against these patches.  So
maybe we don't want to.

If we had a way of releasing experimental, non-default picked up
versions, that would be nice (i.e. Cabal 1.21). No warranty, but
easy enough for GHC devs to say 'cabal install Cabal-1.21
cabal-install-1.21' or something.

Edward

Excerpts from Johan Tibell's message of 2014-08-08 22:02:25 +0100:
> I'm not again putting out another release, but I'd prefer to make it on top
> of 1.20 if possible. Making a 1.22 release takes much more work (RC time,
> etc). Which are the patches in question. Can they easily be cherry-picked
> onto the 1.20 branch? Are there any risk of breakages?
> 
> On Fri, Aug 8, 2014 at 2:00 PM, Edward Z. Yang <ezyang at mit.edu> wrote:
> 
> > Hey all,
> >
> > SPJ pointed out to me today that if you try to run:
> >
> >     cabal install --with-ghc=/path/to/inplace/bin/ghc-stage2
> >
> > with the latest GHC HEAD, this probably will not actually work, because
> > your system installed version of Cabal is probably too old to deal with
> > the new package key stuff in HEAD.  So, how do you get a version
> > of cabal-install (and Cabal) which is new enough to do what you need
> > it to?
> >
> > The trick is to compile Cabal using your /old/ GHC. Step-by-step, this
> > involves cd'ing into libraries/Cabal/Cabal and running `cabal install`
> > (or install it in a sandbox, if you like) and then cd'ing to
> > libraries/Cabal/cabal-install and cabal install'ing that.
> >
> > Cabal devs, is cutting a new release of Cabal and cabal-install in the
> > near future possible? In that case, users can just cabal update; cabal
> > install cabal-install and get a version of Cabal which will work for
> > them.
> >
> > Cheers,
> > Edward
> > _______________________________________________
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> > cabal-devel at haskell.org
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> >