[Haskell-cafe] 1-to-many preprocessor in stack/Cabal builds

[Edward Z. Yang]

OK.

If there is a simple patch which can help support your use case better,
we'd be happy to take it. However, I don't think a design like this is
the right long term plan. The correct long term plan, I think, is to do
something like ToolCabal <https://github.com/TiborIntelSoft/ToolCabal>
and make it so that you can just plug in custom build rules of your own,
which can include preprocessor processing.  This will also fix some of
our other problems, such as the fact that we repeatedly preprocess
executables even when it's not necessary
<https://github.com/haskell/cabal/issues/2432>

I'm hoping to take a crack at this at some point; hopefully your
boilerplate will tide you until then.

Edward

Excerpts from Andrey Sverdlichenko's message of 2016-03-07 10:45:56 -0800:
> Hi Edward,
> 
> I can do with current Cabal, it is just a lot of boilerplate and
> inconvenience.
> What I would like to have as an ideal solution for my problem is a
> preprocessor interface similar to PPSuffixHandler, but with extra
> capabilities.
> It should receive one file as an input, but be able to generate multiple
> modules with the names of its own choosing. And I want the resulting
> modules to be added to all build steps automatically. So it should looks
> approximately like this:
> 
> data SmartPreProcessor = SmartPreProcessor {
>     platformIndependent :: Bool,
>     runPreProcessor :: (FilePath, FilePath) -- Location of the source file
> relative to a base dir
>                     -> Verbosity            -- verbosity
>                     -> FilePath             -- output base dir
>                     -> IO [FilePath]        -- output sources files. Should
> exit if the preprocessor fails
> }
> 
> There may be design objections to such preprocessor, but again, this is an
> ideal solution to my problem.
> 
> On Sun, Mar 6, 2016 at 11:55 PM Edward Z. Yang <ezyang at mit.edu> wrote:
> 
> > Hello Andrey,
> >
> > I do not know what the right way to sovle your problem is, but if it is
> > indeed the case that this cannot be done with Cabal, speaking as a Cabal
> > developer, we definitely should try to fix this.  A bug report
> > would be much appreciated.
> >
> > > So, I have buildHook, copyHook and regHook replaced with wrappers which
> > > change PackageDescription parameter and call original function. Library
> > is
> > > built and installed, but somewhere between build and copy actions there
> > is
> > > still a message "Warning: modules not listed in foo.cabal for library
> > > component (add to other-modules)". I can't identify where it comes from.
> >
> > I'm pretty sure this message comes from Stack; src/Stack/Types/Package.hs.
> >
> > Cheers,
> > Edward
> >