I tried to do this with

    commit 0a12d92a
    Author: Simon Peyton Jones <simonpj@microsoft.com>
    Date:   Wed Dec 13 12:53:26 2017 +0000

    Further improvements to well-kinded types

    The typechecker has the invariant that every type should be well-kinded
    as it stands, without zonking.  See Note [The well-kinded type invariant]
    in TcType.

    That invariant was not being upheld, which led to Trac #14174.  I fixed
    part of it, but T14174a showed that there was more.  This patch finishes
    the job.

But I didn't get it quite right as Trac #14873 showed.

This patch fixes the problem; although I am still a bit unhappy.
(See "A worry" in the HsApp case of tc_infer_hs_type.)