[GHC] #12875: GHC fails to link all StaticPointers-defining modules of a library in an executable

[GHC]

#12875: GHC fails to link all StaticPointers-defining modules of a library in an
executable
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        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  StaticPointers
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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@@ -7,0 +7,1 @@
+

New description:

 Consider that you have a package called `lib` which exposes these modules,
 {{{#!hs
 module ALib.Types where

 data AThing = AThing String
             deriving (Show)


 {-# LANGUAGE StaticPointers #-}
 module ALib.Things where

 import GHC.StaticPtr
 import ALib.Types

 thing1 :: StaticPtr AThing
 thing1 = static (AThing "hello")
 }}}


 Now consider that you have a server which reads a `StaticKey` of
 `StaticPtr AThing` and shows it,
 {{{#!hs
 import ALib.Types

 main :: IO ()
 main = do
     key <- readFingerprint <$> getContents :: IO StaticKey
     Just thing <- unsafeLookupStaticPtr key :: IO (Maybe (StaticPtr
 AThing))
     print $ deRefStaticPtr thing
 }}}

 Naturally this executable will link against `lib`. However, this
 executable as-written will fail if given the key of `ALib.Things.thing1`.
 Fixing this requires that the executable explicitly import and use a
 definition from `ALib.Things`.

 The problem appears to be that the linker elides the `ALib.Things` object
 from the final executable unless it refers to a symbol. Note that things
 also work fine if the server executable is dynamically linked.

--

Comment (by bgamari):

 See https://github.com/bgamari/T12875-repro for a functional example of
 this.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12875#comment:1>
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