[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:  new
        Priority:  normal            |            Milestone:
       Component:  Template Haskell  |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Windows           |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11223            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 The original issue turns out to be simply due to the fact that `inline-c`
 depends on `Win32` (via `directory`), and your program's cabal file states
 a dependency on your local version `Win32a`. `Win32` defines functions
 like `rgb` as wrappers around Windows API macros and your clone `Win32a`
 also defines functions with the same names. So you do have duplicate
 definitions for symbols. The issue doesn't have anything to do with
 `inline-c` besides the fact that it is causing the real `Win32` to be
 linked in.

 The issue is that, unlike symbols that come from Haskell functions, we
 don't mangle the symbols defined in C source files with the package
 identifier. I think there is a ticket about changing this, but for now
 it's a known limitation that you have to ensure that symbol names in C
 files you link in globally unique.

 Using the symbol name `rgb` in `Win32` is really not very good, as it is
 fairly likely to collide with someone else's symbol, and we should change
 that. In the `unix` package, we use symbol names like `__hsunix_ptsname`.
 However using a more GHC-specific symbol name would not help here, since
 you copied the `Win32` source into your own package.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11748#comment:14>
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