[commit: ghc] ghc-8.0: TyCoRep: Restore compatibility with 7.10.1 (56a9f93)

[git at git.haskell.org]

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

On branch  : ghc-8.0
Link       : http://ghc.haskell.org/trac/ghc/changeset/56a9f936357be739fefde111f918531661bede4a/ghc

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

commit 56a9f936357be739fefde111f918531661bede4a
Author: Ben Gamari <bgamari.foss at gmail.com>
Date:   Thu Jan 21 11:19:23 2016 +0100

    TyCoRep: Restore compatibility with 7.10.1
    
    Sadly CallStack wasn't present in 7.10.1, breaking the build when
    bootstrapping from this version.
    
    This patch essentially disables CallStack support for stage1 builds with
    7.10.*. This doesn't seem so unreasonable though as stage2 will still
    work.
    
    Test Plan: Validate with 7.10.1
    
    Reviewers: gridaphobe, jstolarek, austin
    
    Reviewed By: jstolarek
    
    Subscribers: thomie, jstolarek
    
    Differential Revision: https://phabricator.haskell.org/D1812
    
    GHC Trac Issues: #11472
    
    (cherry picked from commit ede055eb230ac33da276f1416678f99e32e83da2)


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

56a9f936357be739fefde111f918531661bede4a
 compiler/types/TyCoRep.hs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/compiler/types/TyCoRep.hs b/compiler/types/TyCoRep.hs
index bd5745a..1522464 100644
--- a/compiler/types/TyCoRep.hs
+++ b/compiler/types/TyCoRep.hs
@@ -151,7 +151,9 @@ import UniqFM
 import qualified Data.Data as Data hiding ( TyCon )
 import Data.List
 import Data.IORef ( IORef )   -- for CoercionHole
+#if MIN_VERSION_GLASGOW_HASKELL(7,10,2,0)
 import GHC.Stack (CallStack)
+#endif
 
 {-
 %************************************************************************
@@ -1816,7 +1818,13 @@ isValidTCvSubst (TCvSubst in_scope tenv cenv) =
 -- | Substitute within a 'Type'
 -- The substitution has to satisfy the invariants described in
 -- Note [Generating the in-scope set for a substitution].
-substTy :: (?callStack :: CallStack) => TCvSubst -> Type  -> Type
+
+substTy ::
+-- CallStack wasn't present in GHC 7.10.1, disable callstacks in stage 1
+#if MIN_VERSION_GLASGOW_HASKELL(7,10,2,0)
+    (?callStack :: CallStack) =>
+#endif
+    TCvSubst -> Type  -> Type
 substTy subst@(TCvSubst in_scope tenv cenv) ty
   | isEmptyTCvSubst subst = ty
   | otherwise = ASSERT2( isValidTCvSubst subst,