Indeed, this was a mistake and I put up a MR last night to hopefully fix it. https://gitlab.haskell.org/ghc/ghc/merge_requests/416 Cheers, Matt On Thu, Feb 21, 2019 at 8:40 AM Simon Peyton Jones wrote:

Ben, Matthew

I believe that ‘master’ fails validate. See Trac #16346.

The question is: how did it get past CI?

The bug would only show up if -dcore-lint was on for libraries.

Simon