Can't install packages with my inplace compiler

[Duncan Coutts]

On Tue, 2014-11-04 at 21:04 +0000, Simon Peyton Jones wrote:
> | Yeah, that's too old; and there's not been a release of a Cabal
> | which is new enough to do what you want.
> 
> Wow!  I'm doing the most basic thing: using Cabal to install a package with a specified GHC.
> 
> I'll try what you suggest.

Actually I'd suggest you use the Cabal and cabal-install that are part
of the ghc source tree, rather than Cabal/cabal-install HEAD. The two
are not always the same.

We try to avoid getting into situations where older cabal binaries
cannot use the current ghc, but it does happen sometimes when we make
changes in ghc that are not fully backwards compatible. In this case we
(or rather I) removed ghc's support for single-file style package dbs
and we later discovered that Cabal was in one place still using that
style. It's plausible that we might want to add back some hack to
ghc-pkg to allow older Cabal versions to work with ghc head.

So in this situation we have to use the Cabal library (that you built
with ghc head), to build cabal-install and its dependencies in the old
style, using Setup.hs. That'll also need the dev version of zlib, due to
the AMP things.

> Duncan: would a release be a good plan?

We tend not to make intermediate releases to support ghc head because
when we're making changes to work with ghc head we're not always in a
good spot to make releases for the general public (we tend to be in the
middle of things and not have enough testing feedback). Also, people
using ghc head already have the corresponding version of
Cabal/cabal-install in their source tree which they can install and use.

On the other hand, when we think we're in a reasonable state with Cabal
testing, and ghc is getting into release mode and we have more people
needing to test ghc head, then of course making a release becomes
important.

My point is that when Edward and I were making all these breaking
changes to Cabal/ghc in the packaging area is exactly the wrong time to
make a cabal release. In this situation we just have to tell ghc hackers
to use the Cabal/cabal-install from the ghc tree.

-- 
Duncan Coutts, Haskell Consultant
Well-Typed LLP, http://www.well-typed.com/