[GHC] #10662: GHC warning shows technical summary of AST instead of the user's code

20 Jul 2015

      #10662: GHC warning shows technical summary of AST instead of the user's code
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              Reporter:  kolmodin    |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:  7.10.2
             Component:  Compiler    |           Version:  7.10.2-rc2
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
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 I got a warning for some code I wrote;

 {{{#!hs
   forkIO (....)
 }}}

 Naturally GHC warns me that I'm throwing away the result, and should write
 like this;

 {{{#!hs
   _ <- forkIO (...)
 }}}

 However, the warning is expressed in a somewhat confusing way, not sure
 this is intentional.

 {{{
 examples/route_guide_client.hs:84:5: Warning:
     A do-notation statement discarded a result of type ‘ThreadId’
     Suppress this warning by saying
       ‘_ <- ($)
               forkIO
               let
                 AbsBinds [] []
                   {Exports: [go <= go
                                <>]
                    Exported types: go :: [L.ByteString] -> IO ()
                                    [LclId, Str=DmdType]
                    Binds: go acc = ...}
               in go []’
     or by using the flag -fno-warn-unused-do-bind

 }}}

 I find it confusing that the warning mentions AbsBinds, exports and types.
 I'd expect a snippet of my code in the warning.

 However, doesn't look like this is a (recent) regression. The same happens
 GHC 7.8.4 and 7.10.1.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10662
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