Wishful thinking: Please allow cabal to solve the attached challenge

[nomeata]

Hi,

in Debian, we use cabal-install with rather extreme command lines to ensure that our package set selection is consistent. For that, we use --constraint foo (== 1.2.3) flags, which works rather well, even with 300 packages.

But I’d also like cabal to help me to find out what upgrades are required to upgrade a specific package. For that, I figured I can use --preference foo (== 1.2.3) --constraint foo (>= 1.2.3) for all our package selection, and --constraint bar (>= 1.2.4) for the package we want to upgrade.

I’ll attach a tarball with a custom cabal config, 00-index.tar.gz (with Debian-specific patches) and a script with a 91k command line (change the paths in the command line and the config file to match yours).

It is a consistent package selection with the exception of scientific, which I want to upgrade. I believe the upgrade is not actually possible (something involving attoparsec and leksah), but I’d like cabal to tell me. Unfortunately, cabal doesn’t finish in a reasonable time yet.

BTW, I can also provide such self-contained examples of large, but consistent package sets, in case you like to have more large example to benchmark and profile.

[nomeata]

Guess github doesn’t allow file attachments. You can pull the tarball at https://people.debian.org/~nomeata/cabal-challenge.tar.gz

[23Skidoo]

/cc @kosmikus

[kosmikus]

Yes, I'd like this, too.

[grayjay]

Cabal can find the conflict relatively quickly now with --reorder-goals (12 seconds on my machine). I'm assuming that this example used GHC-7.6, because 7.4.2 and 7.8.4 both fail with conflicts with base. The error with 7.6.3 is:

Resolving dependencies...
cabal: Could not resolve dependencies:
trying: pandoc-1.12.4.2 (user goal)
next goal: scientific (user goal)
rejecting: scientific-0.3.3.0, scientific-0.3.2.2, scientific-0.3.2.1,
scientific-0.3.2.0, scientific-0.3.1.0, scientific-0.3.0.2,
scientific-0.3.0.1, scientific-0.3.0.0 (conflict: pandoc => scientific>=0.2 &&
<0.3)
rejecting: scientific-0.2.0.2, scientific-0.2.0.1, scientific-0.2.0.0,
scientific-0.1.0.1, scientific-0.1.0.0, scientific-0.0.0.2,
scientific-0.0.0.1, scientific-0.0.0.0 (constraint from command line flag
requires (>=0.3))
Dependency tree exhaustively searched.

I also tried running the command on a package that can be upgraded. I removed the constraint on scientific and upgraded tasty-hunit instead, with the constraint >= 0.5. I also had to comment out the fix for #3199, which adds setup dependencies on Cabal-1.24, since that version isn't in the index. Cabal ran in about 50 seconds and chose to upgrade tasty-hunit, tasty, and tasty-rerun to their latest versions. It also added two new packages, regex-tdfa-rc and unbounded-delays. I don't know how often this works, though. Please reopen if you find examples of packages that aren't handled well.

[kosmikus]

@grayjay What about --count-conflicts on this one?

[grayjay]

I didn't think to try --count-conflicts after it worked with master. --count-conflicts without --reorder-goals takes 26 seconds to upgrade tasty-hunit, and 13 seconds to fail to upgrade scientific. The solver ended up with a larger top-level conflict set for scientific: aeson, attoparsec, conduit, leksah, leksah-server, scientific. The conflict set with just --reorder-goals was pandoc, scientific.

[kosmikus]

Thanks.