[GHC] #10249: GHCi leaky abstraction: error message mentions `ghciStepIO`

[GHC]

#10249: GHCi leaky abstraction: error message mentions `ghciStepIO`
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:  thomie
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  GHCi              |              Version:  7.10.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Incorrect         |            Test Case:
  warning at compile-time            |  ghci/scripts/T10249
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1527,
       Wiki Page:                    |  Phab:D1528
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"71c0cc1531c3e548e47f435432ed31cb79512607/ghc"
 71c0cc15/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="71c0cc1531c3e548e47f435432ed31cb79512607"
 GHCi should not defer typed holes

 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 improves
 the error message for T10248 (it doesn't mention ghciStepIO anymore).
 This is a partial fix for #10249, and a complete fix for #11130.

 Depends on D1526

 Reviewers: simonpj, austin, bgamari

 Reviewed By: simonpj

 Subscribers: simonpj

 Differential Revision: https://phabricator.haskell.org/D1527

 GHC Trac Issues: #10249, #11130
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10249#comment:7>
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