[GHC] #14643: Partial type signatures in spliced TH declarations behave unexpectedly

[GHC]

#14643: Partial type signatures in spliced TH declarations behave unexpectedly
-------------------------------------+-------------------------------------
           Reporter:  mnislaih       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Minimal example:
 {{{#!hs
 {-# LANGUAGE PartialTypeSignatures #-}
 {-# LANGUAGE TemplateHaskell #-}
 module Minimal where

 id [d|
     f :: (Monad m, _) => [m a] -> m [a]
     f' :: (Monad m, _) => [m a] -> m [a]
     f = f'
     f' [] = return []
     f' (x:xx) = f xx
   |]
 }}}

 {{{
 [1 of 1] Compiling Minimal          ( /Users/pepe/Dropbox/code/debug-
 hoed/test/minimal.hs, interpreted )

 /Users/pepe/Dropbox/code/debug-hoed/test/minimal.hs:5:1: warning:
 [-Wpartial-type-signatures]
     • Found type wildcard ‘_’ standing for ‘()’
     • In the type signature:
         f :: (Monad m_a7NN, _) => [m_a7NN a_a7NO] -> m_a7NN [a_a7NO]
   |
 5 | id [d|
   | ^^^^^^...

 /Users/pepe/Dropbox/code/debug-hoed/test/minimal.hs:5:1: warning:
 [-Wpartial-type-signatures]
     • Found type wildcard ‘_’ standing for ‘()’
     • In the type signature:
         f' :: (Monad m_a7NL, _) => [m_a7NL a_a7NM] -> m_a7NL [a_a7NM]
   |
 5 | id [d|
   | ^^^^^^...
 Ok, one module loaded.
  :browse
 f :: (Monad m, Monad m) => [m a] -> m [a]
 f' :: (Monad m, Monad m) => [m a] -> m [a]
 }}}

 Notice the duplicate Monad m constraint.

 Things get even more weird if the type signatures are declared together:
 {{{#!hs
 id [d|
     f, f' :: (Monad m, _) => [m a] -> m [a]
     f = f'
     f' [] = return []
     f' (x:xx) = f xx
      |]
 }}}
 {{{
 [1 of 1] Compiling Minimal          ( /Users/pepe/Dropbox/code/debug-
 hoed/test/minimal.hs, interpreted )

 /Users/pepe/Dropbox/code/debug-hoed/test/minimal.hs:5:1: warning:
 [-Wpartial-type-signatures]
     • Found type wildcard ‘_’ standing for ‘()’
     • In the type signature:
         f :: (Monad m_a88E, _) => [m_a88E a_a88F] -> m_a88E [a_a88F]
   |
 5 | id [d|
   | ^^^^^^...

 /Users/pepe/Dropbox/code/debug-hoed/test/minimal.hs:5:1: warning:
 [-Wpartial-type-signatures]
     • Found type wildcard ‘_’ standing for ‘()’
     • In the type signature:
         f' :: (Monad m_a88E, _) => [m_a88E a_a88F] -> m_a88E [a_a88F]
   |
 5 | id [d|
   | ^^^^^^...
 Ok, one module loaded.
  :browse
 f ::
   (Monad ghc-prim-0.5.1.1:GHC.Types.Any, Monad m) =>
   [ghc-prim-0.5.1.1:GHC.Types.Any ghc-prim-0.5.1.1:GHC.Types.Any]
   -> ghc-prim-0.5.1.1:GHC.Types.Any [ghc-prim-0.5.1.1:GHC.Types.Any]
 f' ::
   (Monad ghc-prim-0.5.1.1:GHC.Types.Any, Monad m) => [m a] -> m [a]
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14643>
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