Yet more work on TcSimplify.simplifyInfer

The proximate cause for this patch is Trac #13482, which pointed out
further subtle interactions between
   - Inferring the most general type of a function
   - A partial type signature for that function

That led me into /further/ changes to the shiny new stuff in
TcSimplify.simplifyInfer, decideQuantification, decideMonoTyVars,
and related functions.

Happily, I was able to make some of it quite a bit simpler,
notably the bit about promoting free tyvars.  I'm happy with
the result.

Moreover I fixed Trac #13524 at the same time.  Happy days.

1 files changed, 22 insertions, 0 deletions

diff --git a/testsuite/tests/partial-sigs/should_compile/T13482.hs b/testsuite/tests/partial-sigs/should_compile/T13482.hs
new file mode 100644
index 0000000000..3af3a74231
--- /dev/null
+++ b/testsuite/tests/partial-sigs/should_compile/T13482.hs
@@ -0,0 +1,22 @@
+{-# LANGUAGE PartialTypeSignatures #-}
+{-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE KindSignatures #-}
+
+module T12382 where
+
+minimal1_noksig :: forall m. ( _ ) => Int -> Bool
+minimal1_noksig _ = (mempty :: m) == (mempty :: m)
+
+minimal1 :: forall (m :: *). _ => Bool
+minimal1 = (mempty :: m) == (mempty :: m)
+
+minimal2 :: forall m. (Eq m, _) => Bool
+minimal2 = (mempty :: m) == (mempty :: m)
+
+minimal3 :: forall m. (Monoid m, _) => Bool
+minimal3 = (mempty :: m) == (mempty :: m)
+
+minimal4 :: forall m. (Monoid m, Eq m) => Bool
+minimal4 = (mempty :: m) == (mempty :: m)
+