[GHC] #9265: Extend PackageId to include version dependency information

[GHC]

#9265: Extend PackageId to include version dependency information
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        Reporter:  ezyang            |            Owner:  ezyang
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Package system    |          Version:  7.9
      Resolution:                    |         Keywords:  backpack
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by rwbarton):

 > We do not have to deal with conflicting "instances" in GHC's package
 resolver: multiple instances can be simultaneously loaded and used in a
 single compiled program. This is because PackageIds are baked into the
 exported linker symbols, so different versions will have different names
 and can peacefully coexist.

 What about packages that statically link against C libraries? Will we
 automatically mangle those C symbol names with the package version hash
 also?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9265#comment:2>
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