[GHC] #14108: GHCi doesn't remember let-less function declarations with -fobject-code

[GHC]

#14108: GHCi doesn't remember let-less function declarations with -fobject-code
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  GHCi              |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 I believe I've identified the culprit. It turns out that the binding for
 `foo2` is discarded entirely during desugaring—in particular, the function
 [http://git.haskell.org/ghc.git/blob/c6462ab02882779d7e33f2cac00cd89a9ac192f1:/compiler/deSugar/Desugar.hs#l280
 addExportFlagsAndRules] is to blame. Normally, the `HscTarget` argument is
 `HscInterpreted`, on which `targetRetainsAllBindings` returns `True`,
 causing `addExportFlagsAndRules` to set the `foo2` `Id` as exported.

 However, when the `HscTarget` argument is, say, `HscAsm` (which can happen
 when `-fobject-code` is enabled), then `targetRetainsAllBindings` returns
 `False`. As a result, `addExportFlagsAndRules` checks if the `foo2` `Id`
 is contained in either the `keep_alive` or `exported` sets—but in GHCi,
 both of those are always empty, so `foo2` isn't marked as exported,
 causing the desugarer to discard it later. Bummer.

 This makes me believe that we should alter `addExportFlagsAndRules` so
 that it always marks local bindings as exported when we're in an
 interactive module (i.e., in GHCi). I'll experiment with this approach.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14108#comment:1>
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