On 10-11-28 09:55 AM, Ketil Malde wrote:
Joachim Breitner<[email protected]> writes:
I would not recommend using --global on Debian/Ubuntu-systems, as it
might interfere with packages installed by Debian.
But 'cabal install --global' installs in /usr/local/, does it not?
And official packages (i.e. debs) put stuff in /usr, so these would be
separate.
Metadata is more important than data.
In the case of Debian/Ubuntu's GHC, both 'cabal install --global' and
'apt-get install' records in /var/lib/ghc-6.12.3/package.conf.d
If you cabal install one version and apt-get another version, sure, they
are two different records in the metadata, no immediate problem.
But how about
cabal install --global binary
apt-get install libghc6-binary-dev
They are the same version (at the time of writing, and assume Ubuntu
10.10) and they will fight for the unique throne of "binary-0.5.0.2" in
the metadata.
The immediate problem: they likely have different ABI hashes because
they're built differently. Suppose you
cabal install --global binary
(suppose it becomes binary-0.5.0.2-300339c66a688207241e4643a9e17721)
cabal install --global I-depend-on-binary
apt-get install libghc6-binary-dev
(this is binary-0.5.0.2-32d59ff8fdfc79aa888e82997612374d in Ubuntu
10.10 i386 32-bit)
Now I-depend-on-binary is hosed. It was built against
binary-0.5.0.2-300339c66a688207241e4643a9e17721 but that's usurped.
OK, who would knowingly usurp his/her own binary-0.5.0.2? Of course no
one knowingly does. But everyone does it unknowingly:
cabal install --global maccatcher
(this brings in binary)
apt-get install libghc6-agda-dev
(this brings in libghc6-binary-dev)
Now maccatcher is hosed.
See also my http://www.vex.net/~trebla/haskell/sicp.xhtml
P.S. Deleting "--global" mitigates this problem but causes some other
problem. I will describe it in my article in the future.
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