cabal install passes --disable-benchmarks to setups built with Cabal lib versions that don't know that flag

[creswick]

This bit me because I do all my work in sandboxes, so the system-installed version of Cabal was 1.12 (which came with ghc-7.2.x, I think 1.14 is needed for --disable-benchmarks).

cabal-installing Cabal-1.14.0 to my user-package db "fixed" the problem, because that cabal was then visible when building setup.hs; however, that's an unfortunate (and non-obvious) requirement. Explicitly specifying the build-dependencies for setup.hs would help with this, and other similar build failures enormously.

I think cabal-install makes the (implicit?) assumption that whatever version of Cabal it was built with is available when it is building setup.hs. That's not a safe assumption any longer -- it would help enormously if we could actually control the environment that setup.hs is built in; as it has /nothing/ to do with the dependencies of the actual program that you're trying to compile.

[refold]

The same probably applies to --disable-tests.