Finish fix for #14880.

The real change that fixes the ticket is described in
Note [Naughty quantification candidates] in TcMType.

Fixing this required reworking candidateQTyVarsOfType, the function
that extracts free variables as candidates for quantification.
One consequence is that we now must be more careful when quantifying:
any skolems around must be quantified manually, and quantifyTyVars
will now only quantify over metavariables. This makes good sense,
as skolems are generally user-written and are listed in the AST.

As a bonus, we now have more control over the ordering of such
skolems.

Along the way, this commit fixes #15711 and refines the fix
to #14552 (by accepted a program that was previously rejected,
as we can now accept that program by zapping variables to Any).

This commit also does a fair amount of rejiggering kind inference
of datatypes. Notably, we now can skip the generalization step
in kcTyClGroup for types with CUSKs, because we get the
kind right the first time. This commit also thus fixes #15743 and
 #15592, which both concern datatype kind generalisation.
(#15591 is also very relevant.) For this aspect of the commit, see
Note [Required, Specified, and Inferred in types] in TcTyClsDecls.

Test cases: dependent/should_fail/T14880{,-2},
            dependent/should_fail/T15743[cd]
            dependent/should_compile/T15743{,e}
            ghci/scripts/T15743b
            polykinds/T15592
            dependent/should_fail/T15591[bc]
            ghci/scripts/T15591

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/deSugar/DsBinds.hs b/compiler/deSugar/DsBinds.hs
index f2ff5dd623..447fea4871 100644
--- a/compiler/deSugar/DsBinds.hs
+++ b/compiler/deSugar/DsBinds.hs
@@ -862,7 +862,7 @@ decomposeRuleLhs dflags orig_bndrs orig_lhs
         -- Add extra tyvar binders: Note [Free tyvars in rule LHS]
         -- and extra dict binders: Note [Free dictionaries in rule LHS]
    mk_extra_bndrs fn_id args
-     = toposortTyVars unbound_tvs ++ unbound_dicts
+     = scopedSort unbound_tvs ++ unbound_dicts
      where
        unbound_tvs   = [ v | v <- unbound_vars, isTyVar v ]
        unbound_dicts = [ mkLocalId (localiseName (idName d)) (idType d)