Re: [GHC] #14916: Missing checks when deriving special classes

25 Mar 2018

      #14916: Missing checks when deriving special classes
-------------------------------------+-------------------------------------
        Reporter:  kosmikus          |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.4.2
       Component:  Compiler (Type    |              Version:  8.2.2
  checker)                           |
      Resolution:  fixed             |             Keywords:  Deriving
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4501
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * status:  patch => closed
 * resolution:   => fixed
 * milestone:   => 8.4.2

Old description:
...
For the following program
{{{
{-# LANGUAGE DeriveAnyClass #-}
module T where
import Data.Coerce
import Data.Typeable
data A = MkA deriving ((~) A)
data B = MkB deriving (Coercible B)
}}}
the deriving clause for `A` is accepted without complaints, and the
deriving clause for `B` fails with the following error:
{{{
T.hs:8:24: error:
    Top-level bindings for unlifted types aren't allowed:
  |
8 | data B = MkB deriving (Coercible B)
  |                        ^^^^^^^^^^^
}}}
Corresponding standalone deriving instances trigger errors
saying "Manual instances of this class are not permitted".
Probably similar error messages should be triggered here.
New description:

 For the following program
 {{{#!hs
 {-# LANGUAGE DeriveAnyClass #-}
 module T where

 import Data.Coerce
 import Data.Typeable

 data A = MkA deriving ((~) A)
 data B = MkB deriving (Coercible B)
 }}}
 the deriving clause for `A` is accepted without complaints, and the
 deriving clause for `B` fails with the following error:
 {{{
 T.hs:8:24: error:
     Top-level bindings for unlifted types aren't allowed:
   |
 8 | data B = MkB deriving (Coercible B)
   |                        ^^^^^^^^^^^
 }}}

 Corresponding standalone deriving instances trigger errors
 saying "Manual instances of this class are not permitted".
 Probably similar error messages should be triggered here.

--

Comment:

 Merged to `ghc-8.4`.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14916#comment:4
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