How to link to Haskell static runtime with cabal and stack without hard coding ghc version? - haskell

Question

I have a project which exports a shared static library and I use the following part in my project.cabal file
executable libsxp.so
main-is: Somefile.hs
default-language: Haskell2010
ghc-options: -shared -dynamic -fPIC -lHSrts-ghc7.10.2
The version of GHC is controlled using Stack, so is there a way wherein I can either get and append the version to make -lHSrts-ghc{version} or is there some config for it? I tried setting
stack build --ghc-options='-O0 -lHSrts-ghc7.10.2'
but it doesn't seem to pick it.
Also to clarify, cabal install is called by Stack and not by me.

Answer 1

Does that cabal file work? If so, then it should be sufficient to do something like this:
executable libsxp.so
ghc-options: -shared -dynamic -fPIC
if impl (ghc >= 7.10.2 && < 7.10.3)
ghc-options: -lHSrts-ghc7.10.2
else if impl (ghc >= 7.10.3 && < 7.10.4)
ghc-options: -lHSrts-ghc7.10.3
else if ...
BTW, why does your executable end in .so? I've never seen that in an executable clause.
Are you sure you're using 7.10.2 and not 7.10.3? Try stack exec -- ghc --version

Answer 2

The general principle is described in this answer: https://stackoverflow.com/a/6034881/1663197
Using the configure style in Cabal, you can write a little configure
script that substitutes a variable for the output of the sdl-config
command. The values will then be replaced in a $foo.buildinfo.in file,
yielding a $foo.buildinfo file, that Cabal will include in the build
process.
First you need to switch your cabal build-type to Configure in project.cabal. Configure style is described in cabal users guide. For build type Configure the contents of Setup.hs must be:
import Distribution.Simple
main = defaultMainWithHooks autoconfUserHooks
In case of handling GHC runtime version you can have a variable #GHC_VERSION# corresponding to it in a project.buildinfo.in file:
ghc-options: -lHSrts-ghc#GHC_VERSION#
Finally you write a configure bash script that gets GHC version as mgsloan suggested and generates project.buildinfo file by substitution of #GHC_VERSION# varibale in project.buildinfo.in file:
GHC_VERSION=$(stack exec -- ghc-pkg field ghc version --simple-output)
sed 's,#GHC_VERSION#,'"$GHC_VERSION"',' project.buildinfo.in > project.buildinfo
This way when build is started it will first execute configure script, then read project.buildinfo file and merge with project.cabal.
Also it may be worth to populate extra-source-files with configure and
project.buildinfo.in; extra-tmp-files with project.buildinfo in project.cabal.
A more sophisticated solution may be inspired by this answer: https://stackoverflow.com/a/2940799/1663197