[GHC] #10303: Make it easier to print stack traces when debugging GHC itself

[GHC]

#10303: Make it easier to print stack traces when debugging GHC itself
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              Reporter:  goldfire    |             Owner:
                  Type:  task        |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.1
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
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 As suggested in [http://mail.haskell.org/pipermail/ghc-
 devs/2015-February/008271.html the mailing list], GHC should have better
 support for printing its own stack trace when profiling is enabled.

 This ticket is to track progress toward this goal.

 There are a few moving parts:

 * Just having `pprTrace` use `traceStack` is a bad idea, because a
 profiled compiler will spew lots and lots and lots of output. Instead, I
 propose a new `pprTraceStack :: String -> SDoc -> a -> a`.

 * Currently, `ASSERT` will print a stack trace, but it's sometimes the
 wrong one. `ASSERT` throws an error; if this error is caught and re-
 thrown, the stack trace is at the re-throw. Instead, it should be at the
 origin.

 * Is it worth adding a new mode in `build.mk` that enables profiling,
 `DEBUG`, and `-fprof-auto`, just to get good stack traces?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10303>
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