[GHC] #16171: "ApplicativeDo" disables -Wunused-do-binds?

[GHC]

#16171: "ApplicativeDo" disables -Wunused-do-binds?
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        Reporter:  eschnett          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.2
      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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Description changed by eschnett:

Old description:

> In the code below, the return value of {{{forkIO}}} is ignored. The
> compiler fails to not warn about this. When I disable the
> {{{ApplicativeDo}}} extension, the warning appears as expected.
>
> {{{
> {-# OPTIONS_GHC -Wall #-}
> {-# LANGUAGE ApplicativeDo #-}
>
> module Example (main) where
>
> import Control.Concurrent
>
> main :: IO ()
> main = do x <- return ()
>           forkIO (putStrLn "hello")
>           putStrLn $ "world" ++ show x
> }}}

New description:

 In the code below, the return value of {{{forkIO}}} is ignored. The
 compiler does not warn about this. When I disable the {{{ApplicativeDo}}}
 extension, the warning appears as expected.

 {{{
 {-# OPTIONS_GHC -Wall #-}
 {-# LANGUAGE ApplicativeDo #-}

 module Example (main) where

 import Control.Concurrent

 main :: IO ()
 main = do x <- return ()
           forkIO (putStrLn "hello")
           putStrLn $ "world" ++ show x
 }}}

--

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16171#comment:1>
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