HEADS UP: Running cabal install with the latest GHC

[Reid Barton]

On Fri, Aug 8, 2014 at 8:00 AM, 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.
>

Hi all,

The new cabal-install I built last month following the instructions above
started failing with recent GHC HEAD with messages like

 ghc: ghc no longer supports single-file style package databases
(dist/package.conf.inplace) use 'ghc-pkg init' to create the database with
the correct format.

I found that repeating these steps with the latest libraries/Cabal
submodule gave me a cabal-install that, so far, appears to be working with
GHC HEAD. So if your cabal-install has stopped working with HEAD, try
building the latest version as outlined in Edward's email.

Cabal wizards, any gotchas with current Cabal & GHC HEAD I should be aware
of?

Regards,
Reid Barton
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