[GHC] #14227: Add -fdefer-ffi-errors flag

[GHC]

#14227: Add -fdefer-ffi-errors flag
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        Reporter:  tysonzero         |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 > The easiest solution to the problem seems to me to be a `-fdefer-ffi-
 errors` flag which replaces any unsupported ffi declaration with a runtime
 error call that gives a similar error message to the one currently given
 at compile time.

 An interesting idea. I believe this wouldn't be too hard to implement; the
 relevant code can be found in `TcForeign.checkCConv`.


 > I would also like a `-fdefer-ffi-errors-no-warn` flag to avoid my
 tooling complaining / emitting a bunch of warnings that don't actually
 help me much.

 I think I would probably instead spell this `-Wno-deferred-ffi-errors` or
 similar.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14227#comment:1>
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