[GHC] #15361: Error message displays redundant equality constraint

[GHC]

#15361: Error message displays redundant equality constraint
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.4.3
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14394            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by RyanGlScott):

 We can fix this issue with the following patch:

 {{{#!diff
 diff --git a/compiler/typecheck/TcErrors.hs
 b/compiler/typecheck/TcErrors.hs
 index 95dc152..1098b1f 100644
 --- a/compiler/typecheck/TcErrors.hs
 +++ b/compiler/typecheck/TcErrors.hs
 @@ -1821,7 +1821,7 @@ pp_givens givens
      where
         ppr_given herald (Implic { ic_given = gs, ic_info = skol_info
                                  , ic_env = env })
 -           = hang (herald <+> pprEvVarTheta gs)
 +           = hang (herald <+> pprEvVarTheta (mkMinimalBySCs evVarPred
 gs))
                  2 (sep [ text "bound by" <+> ppr skol_info
                         , text "at" <+> ppr (tcl_loc env) ])

 }}}

 (Where `pp_givens` is the function that prints out the stuff after `from
 the context:`.) Does this sound like a reasonable approach?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15361#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler