[libcxx] Improve error message when an invalid directory is provided as use_system_cx...

llvm-svn: 347435

diff --git a/libcxx/utils/libcxx/test/config.py b/libcxx/utils/libcxx/test/config.py
index 7467511..abd4b76 100644 (file)
--- a/libcxx/utils/libcxx/test/config.py
+++ b/libcxx/utils/libcxx/test/config.py
@@ -307,7 +307,7 @@ class Configuration(object):
         elif self.use_system_cxx_lib == 'false':
             self.use_system_cxx_lib = False
         elif self.use_system_cxx_lib:
-            assert os.path.isdir(self.use_system_cxx_lib)
+            assert os.path.isdir(self.use_system_cxx_lib), "the specified use_system_cxx_lib parameter (%s) is not a valid directory" % self.use_system_cxx_lib
         self.lit_config.note(
             "inferred use_system_cxx_lib as: %r" % self.use_system_cxx_lib)