Commit 49d9b009 authored by Simon Peyton Jones's avatar Simon Peyton Jones

Fix fundep coverage-condition check for poly-kinds

See Note [Closing over kinds in coverage] in FunDeps.
I'd already fixed this bug once, for Trac #8391, but I put the
call to closeOverKinds in the wrong place, so Trac #10109
failed.  (It checks the /liberal/ coverage condition, which

The fix was easy: move the call to the right place!
parent 7b042d5a
......@@ -382,11 +382,12 @@ checkInstCoverage be_liberal clas theta inst_taus
= NotValid msg
where
(ls,rs) = instFD fd tyvars inst_taus
ls_tvs = closeOverKinds (tyVarsOfTypes ls) -- See Note [Closing over kinds in coverage]
ls_tvs = tyVarsOfTypes ls
rs_tvs = tyVarsOfTypes rs
conservative_ok = rs_tvs `subVarSet` ls_tvs
liberal_ok = rs_tvs `subVarSet` oclose theta ls_tvs
conservative_ok = rs_tvs `subVarSet` closeOverKinds ls_tvs
liberal_ok = rs_tvs `subVarSet` closeOverKinds (oclose theta ls_tvs)
-- closeOverKinds: see Note [Closing over kinds in coverage]
msg = vcat [ sep [ ptext (sLit "The")
<+> ppWhen be_liberal (ptext (sLit "liberal"))
......@@ -419,7 +420,7 @@ Example (Trac #8391), using liberal coverage
instance Bar a (Foo a)
In the instance decl, (a:k) does fix (Foo k a), but only if we notice
that (a:k) fixes k.
that (a:k) fixes k. Trac #10109 is another example.
Note [The liberal coverage condition]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
......
{-# LANGUAGE PolyKinds, MultiParamTypeClasses, FunctionalDependencies,
UndecidableInstances, FlexibleInstances #-}
module T10109 where
data Succ a
class Add (a :: k1) (b :: k2) (ab :: k3) | a b -> ab
instance (Add a b ab) => Add (Succ a) b (Succ ab)
......@@ -448,3 +448,4 @@ test('T10156', normal, compile, [''])
test('T10177', normal, compile, [''])
test('T10185', expect_broken(10185), compile, [''])
test('T10195', normal, compile, [''])
test('T10109', normal, compile, [''])
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