Refine printing of names in unification mis-match

diff --git a/compiler/typecheck/TcUnify.lhs b/compiler/typecheck/TcUnify.lhs
index 2b42d0b..c7082cd 100644 (file)
--- a/compiler/typecheck/TcUnify.lhs
+++ b/compiler/typecheck/TcUnify.lhs
@@ -1617,16 +1617,23 @@ ppr_extra env (TyConApp tc1 _) (TyConApp tc2 _)
     --    Could not match 'T' does not match 'M.T'
     -- which is not helpful
     do { this_mod <- getModule
-       ; return (env, quotes (ppr tc1) <+> ptext SLIT("is defined in") <+> mk_mod this_mod) }
+       ; return (env, quotes (ppr tc1) <+> ptext SLIT("is defined") <+> mk_mod this_mod) }
   where
-    tc_mod = nameModule (getName tc1)
-    tc_pkg = modulePackageId tc_mod
+    tc_mod  = nameModule (getName tc1)
+    tc_pkg  = modulePackageId tc_mod
+    tc2_pkg = modulePackageId (nameModule (getName tc2))
     mk_mod this_mod 
-       | tc_mod == this_mod = ptext SLIT("this module")
-       | otherwise = ptext SLIT("module") <+> quotes (ppr tc_mod) <+> mk_pkg this_mod
-    mk_pkg this_mod
-       | tc_pkg == modulePackageId this_mod = empty
-       | otherwise = ptext SLIT("from package") <+> quotes (ppr tc_pkg)
+       | tc_mod == this_mod = ptext SLIT("in this module")
+
+       | not home_pkg && tc2_pkg /= tc_pkg = pp_pkg
+               -- Suppress the module name if (a) it's from another package
+               --                             (b) other_ty isn't from that same package
+
+       | otherwise = ptext SLIT("in module") <+> quotes (ppr tc_mod) <+> pp_pkg
+       where
+         home_pkg = tc_pkg == modulePackageId this_mod
+         pp_pkg | home_pkg  = empty
+                | otherwise = ptext SLIT("in package") <+> quotes (ppr tc_pkg)
 
 ppr_extra env ty other_ty = return (env, empty)                -- Normal case