C compiler selection in cabal package - haskell

Question

I decided to add some flags to control the way that C source file is compiled (i.e. something like use-clang, use-intel etc.).
C-Sources: c_lib/tiger.c
Include-Dirs: c_lib
Install-Includes: tiger.h
if flag(debug)
GHC-Options: -debug -Wall -fno-warn-orphans
CPP-Options: -DDEBUG
CC-Options: -DDEBUG -g
else
GHC-Options: -Wall -fno-warn-orphans
Question is: which options in descritpion file need to be modified to change C compiler? I did found only CC-Options.

Answer 1

There is no straightforward way, but it is possible.
Assuming that you are using Distribution.Simple, you basically need to add a user hook to the build stage.
All of the following changes need to appear in Setup.hs:
Change main to use a build hook, something like:
main :: IO ()
main = defaultMainWithHooks simpleUserHooks { buildHook = myBuildHook }
Next you need a build hook. It will likely look something like the following:
myBuildHook pkg_descr local_bld_info user_hooks bld_flags =
do
let lib = fromJust (library pkg_descr)
lib_bi = libBuildInfo lib
custom_bi = customFieldsBI lib_bi
cpp_name = fromJust (lookup "x-cc-name" custom_bi)
c_srcs = cSources lib_bi
cc_opts = ccOptions lib_bi
inc_dirs = includeDirs lib_bi
lib_dirs = extraLibDirs lib_bi
bld_dir = buildDir local_bld_info
-- Compile C/C++ sources
putStrLn "invoking my compile phase"
objs <- mapM (compileCxx cpp_name cc_opts inc_dirs bld_dir) c_srcs
-- Remove C/C++ source code from the hooked build (don't change libs)
let lib_bi' = lib_bi { cSources = [] }
lib' = lib { libBuildInfo = lib_bi' }
pkg_descr' = pkg_descr { library = Just lib' }
-- The following line invokes the standard build behaviour
putStrLn "Invoke default build hook"
bh <- buildHook simpleUserHooks pkg_descr' local_bld_info user_hooks bld_flags
return bh
The code above probably needs unpacking a bit. The let clauses are basically about unpacking the required data fields from the structures passed to the build hook. Notice that you can create custom stanzas in your foo.cabal. I have provided the code to support a stanza something like:
x-cc-name: icc
As a means to specify your compiler. Having extracted all of the source files, you map over them using a function to compile a single file (NB: this is sub-optimal in some cases, e.g. those compilers which can efficiently compile multiple source files to produce a single object output and benefit from large scale optimizations, but we'll leave that aside for now).
Last of all, as we've now compiled the C/C++ code, remove it from the build structures before you pass everything on to the default build hook.
Sorry that this is more of a 'HOWTO' than a canned answer, but it should help you to get going.
I should mention that the code is untested. I have adapted it from some work I have been doing on the wxHaskell build system, so I know the idea works fine. The Cabal API is actually pretty well documented - it suffers mainly from being somewhat unstable around some of these areas.

Answer 2

There really doesn't seem to be any way to specify this in a .cabal file; the only thing we seem to have at the moment that would be even remotely useful here is --with-<prog>=path.
I suggest you try filing a ticket against Cabal on the trac.

Answer 3

4.10.1. Replacing the program for one or more phases
-pgmc cmd
        Use cmd as the C compiler.
This works for ghc --make, but I'm not sure how to get Cabal to apply this to the C file compilation.