Cabal flag to build without `template-haskell`

[andreasabel]

QuickCheck has a cabal flag templatehaskell and with constraints: QuickCheck -templatehaskell one can build it without template-haskell.
Such would be useful for containers as well e.g. when one wants to build the GHC-shipped library pretty.

haskell/pretty$ cabal build --enable-tests -c 'QuickCheck -templatehaskell'
Could not resolve dependencies:
[__0] trying: pretty-1.1.3.6 (user goal)
[__1] trying: pretty:*test
[__2] trying: QuickCheck-2.16.0.0 (dependency of pretty *test)
[__3] trying: splitmix-0.1.3.1 (dependency of QuickCheck)
[__4] trying: containers-0.7/installed-f896 (dependency of QuickCheck)
[__5] trying: template-haskell-2.23.0.0/installed-9d0c (dependency of containers)
[__6] next goal: ghc-boot-th (dependency of template-haskell)
[__6] rejecting: ghc-boot-th-9.12.2/installed-9353 (package is broken, missing dependency pretty-1.1.3.6-1375)
[__6] rejecting: ghc-boot-th; 9.10.2, 9.10.1, 9.8.1, 9.6.6, 9.6.3, 9.6.1, 9.4.1, 9.2.2, 9.2.1, 9.0.1, 8.10.2, 8.10.1, 8.8.3, 8.8.1, 8.6.5, 8.6.4, 8.6.1, 8.4.4, 8.4.3, 8.4.2, 8.4.1, 8.2.2, 8.2.1, 8.0.2, 8.0.1 (conflict: template-haskell => ghc-boot-th==9.12.2/installed-9353)
[__6] fail (backjumping, conflict set: ghc-boot-th, template-haskell)

Downstream issue:

• How to build the testsuite? pretty#68

[meooow25]

I don't see a good reason to add such a configuration. Being a GHC boot library template-haskell should always be available.

The pretty build issue seems to have little to do with containers and looks more like a ghc-boot-th problem.

[andreasabel]

For the record: the dependency on template-haskell was introduced in 0.6.6 and first shipped out with GHC 9.8 (0.6.8).