Specify include directories via environment variable

flake.nix

@@ -23,6 +23,10 @@
           targets = [ "x86_64-unknown-linux-gnu" ];
         }
       ));
+      addLibcIncludeDir =
+        ''
+          export C_INCLUDE_PATH="${pkgs.stdenv.cc.libc.dev}/include''${C_INCLUDE_PATH:+:$C_INCLUDE_PATH}"
+        '';
       haskell = (import inputs.nix-haskell { inherit system inputs; } {
         name = "garnet";
         src = ./.;
@@ -44,6 +48,7 @@
               libs = [ pkgs.llvmPackages.libclang ];
             };
             packages.garnet.components.library = {
+              preBuild = addLibcIncludeDir;
               preConfigure = ''
                 mkdir -p rust/target/debug
                 ln -s ${garnet-rs}/include/garnet_rs.h rust/target/debug/garnet_rs.h
@@ -70,6 +75,7 @@
           };
           withHoogle = false;
           withHaddock = true;
+          shellHook = addLibcIncludeDir;
         };
       });
       garnet-rs = crane.buildPackage {

lib/GarnetRs/Raw.hs

@@ -30,17 +30,9 @@ import Language.Haskell.TH
 import System.Process
 
 do
-    systemDirs <- -- TODO bit of a hack
-        map (Dir . T.unpack . T.strip)
-            . concatMap (takeWhile (maybe False ((== ' ') . fst) . T.uncons) . dropWhile T.null . T.lines)
-            . drop 1
-            . T.splitOn "search starts here:"
-            . T.pack
-            . thd3
-            <$> runIO (readProcessWithExitCode "cpp" ["-v"] "")
     withHsBindgen
         def
-            { clang = def{extraIncludeDirs = Pkg "rust/target/debug" : systemDirs}
+            { clang = def{extraIncludeDirs = [Pkg "rust/target/debug"]}
             , fieldNamingStrategy = OmitFieldPrefixes
             }
         def