[Hackage] #466: datadir does not follow prefix on windows (for libs)

[Hackage]

#466: datadir does not follow prefix on windows (for libs)
----------------------------+-----------------------------------------------
  Reporter:  duncan         |        Owner:           
      Type:  defect         |       Status:  new      
  Priority:  normal         |    Milestone:  Cabal-1.8
 Component:  Cabal library  |      Version:  1.6.0.1  
  Severity:  normal         |   Resolution:           
  Keywords:                 |   Difficulty:  normal   
Ghcversion:  6.8.3          |     Platform:  Windows  
----------------------------+-----------------------------------------------
Changes (by duncan):

  * difficulty:  easy (<4 hours) => normal
  * summary:  libdir does not follow prefix on windows => datadir does not
              follow prefix on windows (for libs)

Old description:

> On Windows, for some reason, the `--libdir` is set independently of the
> `--prefix`. This is actually quite annoying because it's not discoverable
> and when you do discover it you've got to set the libdir along with the
> prefix on the command line or in the config file.
>
> Apparently there was some reason why it is done this way. We should find
> out what that reason is and determine if it is valid and if so if there
> is any way to make it work in a less annoying way.
>
> If we think it will not break anything then changing the default is
> trivial.

New description:

 On Windows the `--datadir` is set independently of the `--prefix` (at
 least for libraries). This is actually quite annoying because it's not
 discoverable and when you do discover it you've got to set the datadir
 along with the prefix on the command line or in the config file.

 The problem is to do with relocatable packages and data files.

 Suppose you have a library that has data files. For a hypothetical example
 how about some Unicode library that uses data files of character traits.
 Now we want to use that library in a program and we want to have that
 program be relocatable. That means that at runtime the library needs to be
 able to locate its data files. But the place where the library was
 installed is completely independent of where the .exe is being run from.

 One way to make this appear to work is for the library data directory to
 not really be relocatable, then it looks like we can relocate the .exe and
 have it still work. Of course the .exe is not very re-locatable, in
 particular it cannot be relocated to another machine. This is often the
 use case for relocatable packages on Windows.

 Perhaps another solution would be to place the burden of finding the data
 files on the executable, or at least on the process of preparing the
 relocatable executable. If we made the process of generating a relocatable
 package more explicit we could include in that process checking for
 dependent library packages that use data files. We could then inform the
 packager and/or copy/link the necessary data files into a place where the
 library code will be able to find them relative to the executable. See
 #469.

Comment:

 I was remembering this wrong, it's the datadir not the libdir. Updated the
 description.

 Filed ticket #469 for better support for relocatable packages.

-- 
Ticket URL: <http://hackage.haskell.org/trac/hackage/ticket/466#comment:1>
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