Use `cabal install --enable-tests --dependencies-only --dry-run` instead of `cabal freeze`?

[danclien]

Doing cabal install --enable-tests --dependencies-only --dry-run in a clean sandbox gives similar results to using cabal freeze. This would help resolve/avoid the following issues:

• 1 – Unexpected constraints difference

  • May be not relevant if not using cabal freeze
  • I'm assuming cabal install --enable-tests --dry-run would match cabal sandbox hc-pkg list. I haven't confirmed though.

• 36 – Pass flags to cabal freeze to ensure all targets are included

  • Skips using cabal freeze altogether and grabs the testing dependencies correctly

• 41 – Improve Stackage support

  • Avoids issues with cabal freeze not respecting constraints
  • Should work with Stackage with a cabal.config file located in the app directory
• https://github.com/haskell/cabal/issues/1908 – Self-constraint generated by 'freeze'
  • Avoids requiring Cabal 1.22
  • Cabal 1.22 with ghc-mod is broken without GHC 7.10
  • GHC 7.10 is not fully supported by Stackage yet
  • Added in response to @mietek's comment below

I grabbed the output of both on one of our internal projects, and the output can be seen here. Output from cabal freeze was altered using sed to make differences easier to notice.

Major differences:

• cabal freeze includes packages included with GHC. e.g. The ones listed in /app/ghc/lib/ghc-7.8.4/package.conf.d
• cabal freeze has a cleaner, more consistent output format
  • cabal install --enable-tests --dry-run indicated when there a newer version
  • e.g. blaze-builder-0.3.3.4 (latest: 0.4.0.1)

[mietek]

Thank you. This is a model feature request. Much appreciated.

[mietek]

Getting rid of cabal freeze would also avoid https://github.com/haskell/cabal/issues/1908, which is still an issue for cabal-install versions prior to 1.22.0.0, and requires a workaround.

[mietek]

Another benefit is, the GHC version would not be automatically over-constrained.

Currently, since cabal freeze includes a version constraint for the base package, the GHC version is constrained down to the point release; e.g. base-4.7.0.2 constrains GHC to 7.8.4, and not just 7.8.

As a consequence, declaring HALCYON_GHC_VERSION in a magic file should be allowed.

[mietek]

Replacing cabal freeze would also allow using cabal-install versions prior to 1.20.0.0.

[thorinii]

What's needed to do this? Are we waiting for an update to cabal, or is it parsing a different format, or...?

[mietek]

@thorinii: In a word, time — to design, and to implement.

[mietek]

Perhaps it’d be worth to consider supporting separate sets of version constraints for different GHC versions. Perhaps even separate .halcyon/$GHC_VERSION directories.

[mietek]

I’m sorry. This project is no longer maintained.