Use implicit CallStacks for ASSERT when available

This aids with debugging, since all you have to do to get more
stack frames is add a constraint `(?callStack :: CallStack) =>`.

Old output:
```
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.1.20160107 for x86_64-unknown-linux):
        ASSERT failed!
  file compiler/types/TyCoRep.hs line 1800
  InScope []
  [Xuv :-> n_av5[sk]]
  []
```

New output:
```
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.1.20160107 for x86_64-unknown-linux):
        ASSERT failed!
  CallStack (from ImplicitParams):
  assertPprPanic, called at compiler/types/TyCoRep.hs:1800:95 in
ghc:TyCoRep
  InScope []
  [Xuv :-> n_av5[sk]]
  []
```

Test Plan:
harbormaster
manual testing

Reviewers: austin, gridaphobe, bgamari

Reviewed By: gridaphobe, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1751

1 files changed, 11 insertions, 2 deletions

diff --git a/compiler/utils/Outputable.hs b/compiler/utils/Outputable.hs
index c3bdf5eb79..35a59c6409 100644
--- a/compiler/utils/Outputable.hs
+++ b/compiler/utils/Outputable.hs
@@ -1096,15 +1096,24 @@ warnPprTrace True   file  line  msg x
   where
     heading = hsep [text "WARNING: file", text file <> comma, text "line", int line]
 
+-- | Panic with an assertation failure, recording the given file and
+-- line number. Should typically be accessed with the ASSERT family of macros
+#if __GLASGOW_HASKELL__ > 710
+assertPprPanic :: (?callStack :: CallStack) => String -> Int -> SDoc -> a
+assertPprPanic _file _line msg
+  = pprPanic "ASSERT failed!" doc
+  where
+    doc = sep [ text (prettyCallStack ?callStack)
+              , msg ]
+#else
 assertPprPanic :: String -> Int -> SDoc -> a
--- ^ Panic with an assertation failure, recording the given file and line number.
--- Should typically be accessed with the ASSERT family of macros
 assertPprPanic file line msg
   = pprPanic "ASSERT failed!" doc
   where
     doc = sep [ hsep [ text "file", text file
                      , text "line", int line ]
               , msg ]
+#endif
 
 pprDebugAndThen :: DynFlags -> (String -> a) -> SDoc -> SDoc -> a
 pprDebugAndThen dflags cont heading pretty_msg