bug#30210: pandoc not reproducible

[Ricardo Wurmus]

> The only file that differs is this:
>
>   
> /gnu/store/8ynsssfjjdjbawndmjlnjlqrh027rl9g-ghc-pandoc-1.17.2-check/lib/ghc-7.10.2/ghc-pandoc-1.17.2.conf.d/package.cache
>   
> /gnu/store/8ynsssfjjdjbawndmjlnjlqrh027rl9g-ghc-pandoc-1.17.2/lib/ghc-7.10.2/ghc-pandoc-1.17.2.conf.d/package.cache

At least they seem to contain the same strings albeit in a different
order.  “diff <(strings a|sort) <(strings b|sort)” shows no
differences.  (Of course there could be other differences than order,
which simply don’t appear to be strings.)

> I wonder if we should expect that other Haskell packages are also
> affected by this.

Other packages also have a “package.cache”, but I don’t think they are
used.  The build system creates a new temporary “package.cache” file for
all Haskell packages, and we have a profile hook that creates such a
file for when Haskell packages are installed to profiles.

Could we maybe just delete “package.cache” after the installation phase?

(Even if we can make our packages appear to be deterministic, will they
really be?  This GHC bug sounds bad for us:
https://ghc.haskell.org/trac/ghc/ticket/4012)

--
Ricardo