[GHC] #13838: -Wdeferred-type-errors on a program with main not of type IO () yields "main thread exited (uncaught exception)"

[GHC]

#13838: -Wdeferred-type-errors on a program with main not of type IO () yields
"main thread exited (uncaught exception)"
-------------------------------------+-------------------------------------
        Reporter:  harry             |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13292            |  Differential Rev(s):  Phab:D4708
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"49e423e9940a9122a4a417cfc7580b9984fb49eb/ghc"
 49e423e9/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="49e423e9940a9122a4a417cfc7580b9984fb49eb"
 Put the `ev_binds` of main function inside `runMainIO`

 This ensures that the deferred type error can be emitted correctly.

 For `main` function in `Main` module, we have

     :Main.main = GHC.TopHandler.runMainIO main

 When the type of `main` is not `IO t` and the
 `-fdefer-type-errors` is enabled, the `ev_binds`
 of `main` function will contain deferred type
 errors.

 Previously, the `ev_binds` are bound to `runMainIO main`,
 rather than `main`, the type error exception at runtime
 cannot be handled properly. See Trac #13838.

 This patch fix that.

 Test Plan: make test TEST="T13838"

 Reviewers: bgamari

 Reviewed By: bgamari

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #13838

 Differential Revision: https://phabricator.haskell.org/D4708
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13838#comment:6>
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