Allow building with Cabal-3.0 (GHC 8.8)

[RyanGlScott]

Various minor tweaks are needed to fix the build the custom Setup script with Cabal-3.0:

• configCompilerAux no longer exists in Cabal-3.0. The Setup script imports it but never uses it, so this import can simply be deleted.

• The following types/functions have been deprecated:

  • ProgramConfiguration in favor of ProgramDb
  • rawSystemProgramConf in favor of runDbProgram
  • die in favor of die'

  Incredibly, all of these are available back to Cabal-1.10 with the exception of die', which I define a shim for with CPP.

[RyanGlScott]

The large remaining hurdle to getting cabal-install-3.0 (which GHC 8.8 requires) to work with the current Travis configuration. Since cabal-install-3.0 uses new-build by default, this command now fails:

$ cabal install --only-dependencies --enable-tests --enable-benchmarks --dry -v > installplan.txt
CallStack (from HasCallStack):
  die', called at ./Distribution/Client/CmdInstall.hs:233:5 in main:Distribution.Client.CmdInstall
cabal: --enable-tests was specified, but tests can't be enabled in a remote
package

I can think of two possible ways to work around this:

1. Require cabal-install-2.4.0.0 as the minimum and use cabal v1-install everywhere in .travis.yml
2. Tweak .travis.yml to use cabal v1-install on newer versions of cabal only by using bash tricks (something like if [ $CABALVER -ge 2400 ] ; then CABALV1="cabal v1-"; else CABALV1="cabal " fi)

[RyanGlScott]

A third option would be:

3. Convert .travis.yml over to use new-build everywhere.

This option would also require raising the minimum version of cabal-install used on Travis.

[RyanGlScott]

I've implemented each of options (1)-(3) above to see how each one would work:

1. https://github.com/RyanGlScott/lhs2tex/commit/88d482fb839da1eaca74e42610d607785ea97e0c
2. https://github.com/RyanGlScott/lhs2tex/commit/5db39bee67c52f17f15d9d8d6433178859d80432
3. https://github.com/RyanGlScott/lhs2tex/commit/6be23fd9d05d4a2773a7559b0325d7b95eb8343d

Which approach would you prefer to use?

[RyanGlScott]

Ping @kosmikus

[kosmikus]

@RyanGlScott Thanks, and sorry for the delay. I've merged your option 3.

[RyanGlScott]

Thanks! Could you release these changes to Hackage as well?

[RyanGlScott]

Ping.