[GHC] #11130: GHCi should not defer typed holes

25 Nov 2015

      #11130: GHCi should not defer typed holes
-------------------------------------+-------------------------------------
           Reporter:  thomie         |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.0.1
          Component:  GHCi           |           Version:  7.10.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Incorrect
  Unknown/Multiple                   |  warning at compile-time
          Test Case:                 |        Blocked By:
  ghci/scripts/T10248                |
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 In the function `tcUserStmt` in compiler/typecheck/TcRnDriver.hs, before
 going over the different ways ('plans') to lift an expression typed at the
 prompt into the GHCi monad, `Opt_DeferTypeErrors` is disabled. Here is the
 accompanying comment:
 {{{
          -- Ensure that type errors don't get deferred when type checking
 the
          -- naked expression. Deferring type errors here is unhelpful
 because the
          -- expression gets evaluated right away anyway. It also would
 potentially
          -- emit redundant type-error warnings, one from each plan.
          ; plan <- unsetGOptM Opt_DeferTypeErrors $
 }}}

 Since `Opt_DeferTypeErrors` implies `Opt_DeferTypedHoles`,
 `Opt_DeferTypedHoles` should be disabled here as well. This will improve
 the error message for T10248.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11130
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler