[GHC] #13948: GHC incorrectly suggests a data constructor is in scope in 8.2

[GHC]

#13948: GHC incorrectly suggests a data constructor is in scope in 8.2
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1-rc2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Poor/confusing
  Unknown/Multiple                   |  error message
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #13568
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 After commit 343cb32d0983f576d344a2d04a35c3fd6eecf2c5 (the fix for
 #13568), which debuted in GHC 8.2, GHC thinks that out-of-scope
 identifiers are actually in-scope!

 {{{#!hs
 module Bug where

 f :: T
 f = undefined
 }}}

 In GHC 8.2.1-rc3, the error message is:

 {{{
 $ /opt/ghc/8.2.1/bin/ghc Bug.hs
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )

 Bug.hs:3:6: error:
     Not in scope: type constructor or class ‘T’
     A data constructor of that name is in scope; did you mean DataKinds?
   |
 3 | f :: T
   |      ^
 }}}

 Compare this to GHC 8.0.2, which gives a more sensible error message:

 {{{
 $ /opt/ghc/8.0.2/bin/ghc Bug.hs
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )

 Bug.hs:3:6: error: Not in scope: type constructor or class ‘T’
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13948>
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