On Sat, Sep 11, 2010 at 21:43, Daniel Fischer
On Saturday 11 September 2010 20:38:21, Paolo Giarrusso wrote:
Hi, after Andrew Coppin's odissey [1], I also had a few problem with cabal, which stopped installing new packages. Details will follow; meanwhile, here are some questions prompted by what happened:
- when recompiling a package with ABI changes, does cabal always update dependent packages? It seems "not always"
cabal will not automatically update packages which depend on an updated package. Since it doesn't keep a record of packages depending on foo, it would have to check all installed packages on every update to do that.
ghc-pkg has such a dependency database, and cabal used it to correctly recompile other packages broken by an upgrade, but not the Cabal library, which resulted in linking errors for Setup.hs and impossibility of further upgrades.
- it didn't update itself, nor refuse the breaking upgrade, and the ABI breakage caused linker errors on Setup.hs. Luckily, cabal was already linked so I could always use it for queries. - can cabal extract and check dependencies as specified in the .hi files?
No.
I had a broken dependency which I could see with "grep" but not otherwise.
ghc-pkg check?
I tried that, but it didn't notice any breakage. As far as I understand, a package won't depend on packages which were hidden during its build, and all available packages will be recorded as dependencies in the ghc-pkg DB. Yet, for some reason this did not work.
- is there a "specification" of which are the "core" packages?
"core" as in *do not update*?
Yep, as in the output of "cabal upgrade" ("Note that it is generally not recommended to upgrade core packages."), and in the Cabal FAQ I linked. Note that cabal install --help gives no warning, which makes a huge difference - I need to try "cabal upgrade" to learn what I shouldn't try to install.
Basically, what comes with GHC shouldn't be updated. Though I heard updating Cabal was okay.
I did update Cabal here to the latest version, while still using GHC 6.10.4 (I'll upgrade that later). My experience suggests that the answer is probably "ghc and cabal dependencies", and that cabal should have special handling for this case, as suggested in the other mail: recompile core dependencies, any broken package, and only _then_ reinstall everything together - in my case, its choices broke package upgrade - I was installing just pandoc. I could have done something not so good before, but the final damage was cabal's choice.
Not sure if this is more useful as a bug report or as discussion, or if I just misused cabal and it's the only perfect software in the world; still I wanted to share my experience.
It's not perfect, and its guards against users breaking their package dbs aren't strong enough yet. But I wouldn't want to go back to a Haskell without it.
Agreed on both - I want my criticism to be constructive, even if I might have phrased it not perfectly. And when I admitted that maybe cabal was perfect, and maybe I used it badly, it might have sounded as ironic, but I did mean it, even if I tried my best to check that it wasn't the case. -- Paolo Giarrusso - Ph.D. Student http://www.informatik.uni-marburg.de/~pgiarrusso/