pythonPackages.xgboost: fix build

The setup.py of `python-package` contains some path resolution magic to
find `libxgboost.so` which is needed for the python API.

Unfortunately the code is incompatible with Nix as it isn't compatible
with the store-based structure for each package and tries to express the
location of the shared object with relative paths.

The detection in `setup.py` and `xgboost/libpath.py` has been either
removed entirely or patched to link to the proper store path of the
`libxgboost` build input.

See https://hydra.nixos.org/build/77702715 for further reference.

pkgs/development/python-modules/xgboost/default.nix

@@ -3,30 +3,28 @@
 , nose
 , scipy
 , xgboost
+, substituteAll
 }:
 
 buildPythonPackage rec {
   pname = "xgboost";
   inherit (xgboost) version src meta;
 
+  patches = [
+    (substituteAll {
+      src = ./lib-path-for-python.patch;
+      libpath = "${xgboost}/lib";
+    })
+  ];
+
+  postPatch = "cd python-package";
+
   propagatedBuildInputs = [ scipy ];
+  buildInputs = [ xgboost ];
   checkInputs = [ nose ];
 
-  postPatch = let
-    libname = "libxgboost.${stdenv.hostPlatform.extensions.sharedLibrary}";
-
-  in ''
-    cd python-package
-
-    sed "s/CURRENT_DIR = os.path.dirname(__file__)/CURRENT_DIR = os.path.abspath(os.path.dirname(__file__))/g" -i setup.py
-    sed "/^LIB_PATH.*/a LIB_PATH = [os.path.relpath(LIB_PATH[0], CURRENT_DIR)]" -i setup.py
-    cat <<EOF >xgboost/libpath.py
-    def find_lib_path():
-      return ["${xgboost}/lib/${libname}"]
-    EOF
-  '';
-
-  postInstall = ''
-    rm -rf $out/xgboost
+  checkPhase = ''
+    ln -sf ../demo .
+    nosetests ../tests/python
   '';
 }