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    Put the `ev_binds` of main function inside `runMainIO` · 49e423e9
    Tao He authored
    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
    49e423e9