[Haskell-cafe] Deprecating STM invariant mechanism

tl;dr. Do you use Control.Monad.STM.always? If so say so on this [1] proposal otherwise the interface may be removed. Hello everyone, GHC's STM subsystem has long had the ability to run user-specified invariant checks when committing transactions, embodied by the Control.Monad.STM.always and alwaysSucceeds functions. However, if Hackage is any indication this feature has seen very little use of the past ten years. In fact, it has very likely been quite broken (#14310) for this entire duration. Consequently, I suggest that we begin deprecating the mechanism. See the deprecation Proposal [1] for full details. Please leave a comment if you object. Cheers, - Ben [1] https://github.com/ghc-proposals/ghc-proposals/pull/77