[commit: ghc] wip/type-app: Wibble to TypeEqOrigin for better errors (25aa251)

[git at git.haskell.org]

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

On branch  : wip/type-app
Link       : http://ghc.haskell.org/trac/ghc/changeset/25aa2519b7ffed668bd1a22e80830865d8b4f840/ghc

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

commit 25aa2519b7ffed668bd1a22e80830865d8b4f840
Author: Richard Eisenberg <eir at cis.upenn.edu>
Date:   Wed Aug 5 08:36:00 2015 -0400

    Wibble to TypeEqOrigin for better errors


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

25aa2519b7ffed668bd1a22e80830865d8b4f840
 compiler/typecheck/TcUnify.hs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/compiler/typecheck/TcUnify.hs b/compiler/typecheck/TcUnify.hs
index 7bee699..7dbe72e 100644
--- a/compiler/typecheck/TcUnify.hs
+++ b/compiler/typecheck/TcUnify.hs
@@ -726,7 +726,9 @@ tc_sub_type_ds eq_orig inst_orig ctxt ty_actual ty_expected
      -- typecheck/should_compile/T4284.
                  |  otherwise
                  -> do { (wrap, rho_a) <- deeplyInstantiate inst_orig ty_actual
-                       ; cow <- uType eq_orig rho_a ty_expected
+                       ; cow <- unifyType rho_a ty_expected
+                            -- NB: unifyType, not uType. We want to refresh
+                            -- the TypeEqOrigin to use the inst'ed type
                        ; return (coToHsWrapper cow <.> wrap) } }
 
     go (FunTy act_arg act_res) (FunTy exp_arg exp_res)