[GHC] #11748: GHC runtime linker: fatal error: I found a duplicate definition for symbol

[GHC]

#11748: GHC runtime linker: fatal error: I found a duplicate definition for symbol
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        Reporter:  jeiea             |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
  (Linking)                          |
      Resolution:  duplicate         |             Keywords:
Operating System:  Windows           |         Architecture:  x86_64
 Type of failure:  Compile-time      |  (amd64)
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11223            |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by Phyx-):

 * status:  new => closed
 * resolution:   => duplicate
 * related:   => #11223


Comment:

 Right, looking at it more closely, I think I understand the problem.

 The `Win32` package already provides a function named `rgb`.

 Due to the call `C.include "<Windows.h>"` in `Lib.hs`. The TH seems to be
 producing another function called `rgb` and hence the duplicate symbols
 error.

 GHC 7.x uses the old runtime linker which greedily loads symbols. So even
 though you don't use any symbols from the `Win32` package. Because you're
 linking against it an error is given.

 The second issue is that it's linking against the full `Win32.o` object
 file that cabal produces instead of the `Win32.a` file.

 In any case, you can't solve this in 7.10.3, you need the fix of #11223.

 So this is a combination of things, but I'll mark it as a duplicate since
 for it to work you'll need GHC 8.0.

 Feel free to re-open it if that doesn't solve it.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11748#comment:8>
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