[commit: ghc] ghc-generics1: Only output generic instances with -ddump-deriv when there is something to output (f5f2210)

[José Pedro Magalhães]

Repository : ssh://darcs.haskell.org//srv/darcs/ghc

On branch  : ghc-generics1

http://hackage.haskell.org/trac/ghc/changeset/f5f22107e1fcfecdfaab1a8d99af4b1763d3a4cb

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

commit f5f22107e1fcfecdfaab1a8d99af4b1763d3a4cb
Author: Jose Pedro Magalhaes <jpm at cs.uu.nl>
Date:   Sun Apr 22 10:49:00 2012 +0200

    Only output generic instances with -ddump-deriv when there is something to output

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

 compiler/typecheck/TcDeriv.lhs |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs
index 0e2f855..512b21f 100644
--- a/compiler/typecheck/TcDeriv.lhs
+++ b/compiler/typecheck/TcDeriv.lhs
@@ -335,9 +335,10 @@ tcDeriving tycl_decls inst_decls deriv_decls
         ; (inst_info, rn_binds, rn_dus) <-
             renameDeriv is_boot (inst_infos ++ (bagToList extraInstances)) binds
 
-	; dflags <- getDynFlags
-	; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
-	         (ddump_deriving inst_info rn_binds newTyCons famInsts))
+        ; dflags <- getDynFlags
+        ; unless (isEmptyBag inst_info) $
+            liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
+                   (ddump_deriving inst_info rn_binds newTyCons famInsts))
 
         ; let all_tycons = map ATyCon (bagToList newTyCons)
         ; gbl_env <- tcExtendGlobalEnv all_tycons $