[GHC] #15832: returnIO/bindIO destroys runtime explicit stack information in some cases

[GHC]

#15832: returnIO/bindIO destroys runtime explicit stack information in some cases
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        Reporter:  infinity0         |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by infinity0):

 OK, but then how do I get a proper "evaluated by" stack trace? From
 [https://github.com/ghc/ghc/blob/f877d9cc99dd1ba0c038e70527031e9ba0934cd3/rts/Profiling.c#L929
 here] it seems that only CAF stacks can be traversed to the "evaluated by"
 stacks. Stacks that don't come from a CAF, can't be traversed further to
 see what caused the evaluation of an error/bottom value.

 In both cases, I am creating an `X` with a bottom inside it. This is a
 decently common pattern used in Haskell, the intent is that I never
 evaluate the bottom. However, programmers make mistakes and it's nice to
 be able to get a stack trace showing me what was trying to evaluate the
 bottom.

 In the good case, I can see both (a) the stack that created the bottom
 value and (b) the stack that caused the evaluation of bottom. In the bad
 case, I can only see (a) and I can't see (b), making things very hard to
 debug.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15832#comment:5>
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