Yep, of course. (I sometimes get the feeling that a less good way people do this is by just not documenting the feature :o) Excerpts from Paolo G. Giarrusso's message of 2016-07-17 04:27:14 -0700:
Edward Z. Yang
writes: Excerpts from Herbert Valerio Riedel's message of 2016-07-13 23:40:06 -0700:
I.e. write up a specification/proposal outlining motivation (i.e. what problem does this solve), specify what the changes are exactly (syntax & semantics), what the consequences are, and so on.
Then we inevitably need some criteria to decide whether a proposal is accepted and approved for implementation. This could be formally in the hands of the core library committee together with the Hackage trustees (since we do have quite some experience with .cabal files and care a lot about the Hackage ecosystem).
Why can't we release experimental changes to the Cabal specification? Neither setup-depends nor convenience libraries went through any formal proposal mechanism. If a feature is good people will start using it and we will have to continue supporting it. If a feature is bad/not useful we can yank it from the next release; anyone using an experimental feature like this isn't trying to maximize their Cabal compatibility anyway.
Important nitpick: to do that, experimental features should be marked as experimental and this policy should be made explicit. That'd be kinder to the one user who starts using it without realizing.
I guess that goes without saying (probably in ways I don't realize), but hey :-D