[GHC] #14106: Out of scope errors appear after type errors caused by them

[GHC]

#14106: Out of scope errors appear after type errors caused by them
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           Reporter:  EyalLotem      |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Poor/confusing
  Unknown/Multiple                   |  error message
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Example:

   import Control.Lens (_Just, (&))
   main = Just 5 & _Just .~ 100 & print

 .~ is out of scope, the error output:

 ghc-error.hs:2:17-21: error: …
     • Couldn't match type ‘Maybe’ with ‘p0 a0’
       Expected type: Maybe (f0 b0) -> p0 (Maybe a0) (f0 (Maybe b0))
         Actual type: p0 a0 (f0 b0) -> p0 (Maybe a0) (f0 (Maybe b0))
     • In the second argument of ‘(&)’, namely ‘_Just’
       In the first argument of ‘(.~)’, namely ‘Just 5 & _Just’
       In the expression: (.~) Just 5 & _Just 100 & print
 ghc-error.hs:2:23-24: error: …
     • Variable not in scope:
         (.~) :: p0 (Maybe a0) (f0 (Maybe b0)) -> IO () -> t
     • Perhaps you meant ‘.’ (imported from Prelude)
       Perhaps you want to add ‘.~’ to the import list in the import of
       ‘Control.Lens’ (/home/eyal/devel/test/ghc-error.hs:1:1-32).
 Compilation failed.

 In larger examples, the out of scope error can be buried deep down.

 In the case of operators - the fixity is unknown so it can even cause the
 parse to go wrong - and very weird type errors to result from that.

 Out of scope errors should be put BEFORE any type errors that might be
 caused by them.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14106>
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