Rebase and upgrade to pex 1.6.3.

3rdparty/python/requirements.txt

@@ -17,7 +17,7 @@ more-itertools<6.0.0 ; python_version<'3'
 packaging==16.8
 parameterized==0.6.1
 pathspec==0.5.9
-pex==1.6.2
+pex==1.6.3
 psutil==5.4.8
 pycodestyle==2.4.0
 pyflakes==2.0.0

src/python/pants/backend/python/interpreter_cache.py

@@ -184,5 +184,5 @@ def _purge_interpreter(self, interpreter_dir):
     except Exception as e:
       logger.warn(
         'Caught exception {!r} during interpreter purge. Please run `./pants clean-all`!'
-          .format(e)
+        .format(e)
       )

src/python/pants/backend/python/tasks/select_interpreter.py

@@ -15,7 +15,6 @@
 from pants.backend.python.interpreter_cache import PythonInterpreterCache
 from pants.backend.python.targets.python_requirement_library import PythonRequirementLibrary
 from pants.backend.python.targets.python_target import PythonTarget
-from pants.base.exceptions import TaskError
 from pants.base.fingerprint_strategy import DefaultFingerprintHashingMixin, FingerprintStrategy
 from pants.invalidation.cache_manager import VersionedTargetSet
 from pants.task.task import Task

src/python/pants/bin/pants_loader.py

@@ -12,6 +12,8 @@
 from builtins import object
 from textwrap import dedent
 
+from pex.pex_warnings import PEXWarning
+
 
 class PantsLoader(object):
   """Loads and executes entrypoints."""
@@ -46,7 +48,7 @@ def setup_warnings():
 
     # If we're running from a pex, suppress pex warnings about transitive dependencies that do not
     # properly declare dependencies on setuptools to support their namespace packages.
-    warnings.filterwarnings('ignore', category=UserWarning, module='pex')
+    warnings.filterwarnings('ignore', category=PEXWarning, module='pex')
 
     # TODO: Future has a pending PR to fix deprecation warnings at https://github.com/PythonCharmers/python-future/pull/421.
     # Remove this filter once that gets merged.