[commit: ghc] master: A tiny bit more tc tracing (086b483)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/086b4836c4b279d5ae0e330719e1a679dd16392e/ghc

>---------------------------------------------------------------

commit 086b4836c4b279d5ae0e330719e1a679dd16392e
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Fri Nov 25 11:43:10 2016 +0000

    A tiny bit more tc tracing


>---------------------------------------------------------------

086b4836c4b279d5ae0e330719e1a679dd16392e
 compiler/typecheck/TcUnify.hs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/compiler/typecheck/TcUnify.hs b/compiler/typecheck/TcUnify.hs
index 12502c6..fa7c517 100644
--- a/compiler/typecheck/TcUnify.hs
+++ b/compiler/typecheck/TcUnify.hs
@@ -684,7 +684,10 @@ tc_sub_type_ds :: CtOrigin    -- used when calling uType
 -- Here is where the work actually happens!
 -- Precondition: ty_expected is deeply skolemised
 tc_sub_type_ds eq_orig inst_orig ctxt ty_actual ty_expected
-  = go ty_actual ty_expected
+  = do { traceTc "tc_sub_type_ds" $
+         vcat [ text "ty_actual   =" <+> ppr ty_actual
+              , text "ty_expected =" <+> ppr ty_expected ]
+       ; go ty_actual ty_expected }
   where
     go ty_a ty_e | Just ty_a' <- coreView ty_a = go ty_a' ty_e
                  | Just ty_e' <- coreView ty_e = go ty_a  ty_e'