Can't build current HEAD

[Jan Stolarek]

I am unable to build current HEAD. I'm getting a build error in Outputable module:

compiler/utils/Outputable.hs:1046:28:
    Not in scope: type constructor or class ‘CallStack’

compiler/utils/Outputable.hs:1047:23: Not in scope: ‘showCallStack’

The most likely culprit is 80d7ce8038a100f6797a89755c893c6f67f18a30, which added this:

#if __GLASGOW_HASKELL__ >= 710
pprSTrace :: (?location :: CallStack) => SDoc -> a -> a                                                                                  
pprSTrace = pprTrace (showCallStack ?location)
#else
pprSTrace :: SDoc -> a -> a
pprSTrace = pprTrace "no callstack info"
#endif

The most interesting thing is that if I change the definition of pprSTrace in the first branch of 
#if to be identical to the definition in the second branch, then I get warnings that GHC.Stack 
and GHC.Exception imports are redundant. Any ideas what might be going on here? I'm compiling 
using GHC 7.10.1. This happens in a clean build tree.

Janek

---
Politechnika Łódzka
Lodz University of Technology

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