nix package: add wrapper from nixpkgs#clang-tools

packaging/nix/default.nix

@@ -4,13 +4,20 @@
   pkg-config,
   installShellFiles,
   libclang,
+  clang,
+  llvmPackages,
   libllvm,
   yaml-cpp,
+  enableLibcxx ? false,
 }:
 stdenv.mkDerivation {
   name = "clang-uml";
   src = ../..;
 
+  # variables for substituteAll
+  unwrapped = llvmPackages.clang-unwrapped;
+  clang = if enableLibcxx then llvmPackages.libcxxClang else llvmPackages.clang;
+
   nativeBuildInputs = [
     cmake
     pkg-config
@@ -18,12 +25,14 @@ stdenv.mkDerivation {
   ];
 
   buildInputs = [
+    clang
     libclang
     libllvm
     yaml-cpp
   ];
 
   postInstall = ''
+    substituteAll ${./wrapper} $out/bin/clang-uml-wrapped
     installShellCompletion --bash $src/packaging/autocomplete/clang-uml
     installShellCompletion --zsh $src/packaging/autocomplete/_clang-uml
   '';

packaging/nix/wrapper

@@ -0,0 +1,31 @@
+#!/bin/sh
+# This file is copied from https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/tools/clang-tools/wrapper
+# The clang-tools wrapper is commonly used together with the clang package on
+# nix, because without the wrapper, clang tools fail to find stdlib includes on
+# nix.
+
+buildcpath() {
+  local path after
+  while (( $# )); do
+    case $1 in
+        -isystem)
+            shift
+            path=$path${path:+':'}$1
+            ;;
+        -idirafter)
+            shift
+            after=$after${after:+':'}$1
+            ;;
+    esac
+    shift
+  done
+  echo $path${after:+':'}$after
+}
+
+export CPATH=${CPATH}${CPATH:+':'}$(buildcpath ${NIX_CFLAGS_COMPILE} \
+                                               $(<@clang@/nix-support/libc-cflags)):@clang@/resource-root/include
+export CPLUS_INCLUDE_PATH=${CPLUS_INCLUDE_PATH}${CPLUS_INCLUDE_PATH:+':'}$(buildcpath ${NIX_CFLAGS_COMPILE} \
+                                                                                      $(<@clang@/nix-support/libcxx-cxxflags) \
+                                                                                      $(<@clang@/nix-support/libc-cflags)):@clang@/resource-root/include
+
+exec -a "$0" @unwrapped@/bin/$(basename $0) "$@"