[GHC] #12691: Refine the behaviour of -dno-debug-output and -dtrace-level

[GHC]

#12691: Refine the behaviour of -dno-debug-output and -dtrace-level
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           Reporter:  mpickering     |             Owner:
               Type:  task           |            Status:  new
           Priority:  low            |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 It wasn't clear to me what these flags should do and what they should turn
 off.

 From the user guide.

  `-dno-debug-output`:: Suppress any unsolicited debugging output. When GHC
 has been built with the  DEBUG option it occasionally emits debug output
 of interest to developers. The extra output can confuse the testing
 framework and cause bogus test failures, so this flag is provided to turn
 it off.

  `-dtrace-level`:: Not present

 `-dno-debug-output` currently suppresses the output of `-ddump-tc-trace`
 which is certainly not "unsolicited". It should be used, and is,  in
 `Outputable` to suppress the output of `pprTrace`.

 `dtrace-level` is used in a few places but always as if was a boolean
 flag. I don't really see what the point of it is. The only commit which
 mentions it is "8cdb98b9909561671ab4e61c90ebb12504478e4d" and I can't find
 the origin of the flag. I think we should just remove it.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12691>
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