WIP: Redesign `cabal {upload,haddock,check,sdist}` to provide a better Cabal/Hackage UX

[hvr]

This ticket is here to remind me to write down a new workflow design involving the commands

• cabal sdist
• cabal check
• cabal haddock
• cabal upload

and their interactions to make it more convenient for users, as well as improve quality of Hackage uploads a bit.

The basic gist is that cabal upload shall provide a convenient way to perform (more or less) the following sequence of commands (and sdist/check/haddock should be augmented consistently):

• cabal sdist
• unpack the just generated tarball $SRCTAR in a temp folder, and chdir(2) to it
• echo 'packages: .' > cabal.project
• cabal new-build
• cabal new-test
• cabal new-benchmark
• cabal new-haddock --for-hackage
• cabal upload $OLDPWD/dist/$SRCTAR
• cabal upload -d dist/$DOCTAR

This all without sacrificing control over the individual phases if the user needs it.

/cc @glguy who suggested something like this to me

[ezyang]

Sure why not. I don't upload sdists all that often so I can't assess if this fills a need.

[ezyang]

@hvr when are you aiming this for? I guess not 2.0? How about 2.2?

[hvr]

@ezyang yeah, 2.2 is more realistic; it'd be useful to have more pieces working (new-test/new-haddock) before tackling this one; and also to combine this with tge switch to new-build as default