[Haskell-cafe] Cabal and autogenerated files

[Duncan Coutts]

On Fri, 2009-11-13 at 15:24 +0000, Jeremy O'Donoghue wrote:

> > So I take it that these modules are generated "from nothing" rather than
> > something like happy/alex pre-processors where the .hs files are
> > generated from .y/.x files. Cabal supports the latter fairly well and
> > you can add custom pre-processors in this style. It doesn't really
> > support generating modules out of thin-air in the build step (though it
> > does this internally for the Paths_pkgname module).
> 
> They don't come from nothing as they are derived from a C header file
> and an Eiffel interface (for historical reasons).

Ok, but not files in a 1:1 correspondence with the modules you generate.
It's more like a bunch of files used to generate another bunch of files,
with no simple naming convention to relate the two.

> It sounds as though the custom preprocessor approach is closest to what
> we have/need.

Cabal's simple notion of preprocessor really only covers the case where
you've got:

Foo/Bar.hs generated from Foo/Bar.some-other-extension

The pre-processors are registered by the extension and the Cabal
pre-processing step decides what pre-processors to run by looking for
files with known extensions.

> We have a custom config hook containing the following:
> 
> myConfHook :: (Either GenericPackageDescription PackageDescription,
> HookedBuildInfo) -> ConfigFlags -> IO LocalBuildInfo
> myConfHook (pkg0, pbi) flags = do
>     createDirectoryIfMissing True wxcoreDirectory
>     system $ "wxdirect -t --wxc " ++ sourceDirectory ++ " -o " ++
>     wxcoreDirectory ++ " " ++ wxcoreIncludeFile
>     system $ "wxdirect -i --wxc " ++ sourceDirectory ++ " -o " ++
>     wxcoreDirectory ++ " " ++ wxcoreIncludeFile
>     system $ "wxdirect -c --wxc " ++ sourceDirectory ++ " -o " ++
>     wxcoreDirectory ++ " " ++ wxcoreIncludeFile
>     system $ "wxdirect -d --wxc " ++ sourceDirectory ++ " -o " ++
>     wxcoreDirectory ++ " " ++ intercalate " " eiffelFiles
> 
> In this case, wxcoreDirectory resolves to
> "dist/build/autogen/Graphics/UI/WXCore".
> 
> The calls to wxdirect generate a number of haskell files as output
> (currently in dist/build/autogen).
> 
> Regards
> Jeremy