Simplify pytest configuration.

+ Use `--rootdir` to set the rootdir ahead of time and use the buildroot
  for sensible RHS paths in `-v` output (previously we only had sensible
  LHS paths via the `NodeRenamerPlugin`). This option was introduced
  relatively recently in 3.5.0:
    https://docs.pytest.org/en/latest/changelog.html#pytest-3-5-0-2018-03-21
    pytest-dev/pytest#1642
+ Control the `.pytest_cachedir` location with `-o` and move it into the
  task workdir (defaults to the `--rootdir` otherwise).
+ Simplify `pytest.ini` nullification by pointing to os.devnull instead
  of embedding an empty `pytest.ini` in the pytest pex.

src/python/pants/backend/python/tasks/pytest/plugin.py

@@ -73,11 +73,6 @@ def is_conftest(itm):
 
 def pytest_addoption(parser):
   group = parser.getgroup('pants', 'Pants testing support')
-  group.addoption('--pants-rootdir-comm-path',
-                  dest='rootdir_comm_path',
-                  action='store',
-                  metavar='PATH',
-                  help='Path to a file to write the pytest rootdir to.')
   group.addoption('--pants-sources-map-path',
                   dest='sources_map_path',
                   action='store',
@@ -105,9 +100,6 @@ def pytest_configure(config):
     return
 
   rootdir = str(config.rootdir)
-  rootdir_comm_path = config.getoption('rootdir_comm_path')
-  with open(rootdir_comm_path, 'w') as fp:
-    fp.write(rootdir)
 
   sources_map_path = config.getoption('sources_map_path')
   with open(sources_map_path) as fp:

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

@@ -4,7 +4,6 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
-import os
 from builtins import object
 
 import pkg_resources
@@ -72,14 +71,6 @@ def interpreter(self):
       """
       return self._interpreter
 
-    @property
-    def config_path(self):
-      """Return the absolute path of the `pytest.ini` config file in this pytest binary.
-
-      :rtype: str
-      """
-      return os.path.join(self._pex.path(), 'pytest.ini')
-
   @classmethod
   def implementation_version(cls):
     return super(PytestPrep, cls).implementation_version() + [('PytestPrep', 2)]
@@ -98,7 +89,6 @@ def _module_resource(cls, module_name, resource_relpath):
                          content=pkg_resources.resource_string(__name__, resource_relpath))
 
   def extra_files(self):
-    yield self.ExtraFile.empty('pytest.ini')
     yield self._module_resource(self.PytestBinary.pytest_plugin_module, 'pytest/plugin.py')
     yield self._module_resource(self.PytestBinary.coverage_plugin_module, 'coverage/plugin.py')
 

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

@@ -80,7 +80,7 @@ class PytestResult(TestResult):
     # This is returned by pytest when no tests are collected (EXIT_NOTESTSCOLLECTED).
     # We already short-circuit test runs with no test _targets_ to return 0 emulated exit codes and
     # we should do the same for cases when there are test targets but tests themselves have been
-    # de-selected out of band via `py.test -k`.
+    # de-selected out of band via `pytest -k`.
     5
   )
 
@@ -378,34 +378,33 @@ def _pants_pytest_plugin_args(self, sources_map):
     # uses all arguments that look like paths to compute its rootdir, and we want
     # it to pick the buildroot.
     with temporary_dir(root_dir=self.workdir) as comm_dir:
-      rootdir_comm_path = os.path.join(comm_dir, 'pytest_rootdir.path')
-
-      def get_pytest_rootdir():
-        with open(rootdir_comm_path, 'r') as fp:
-          return fp.read()
-
       sources_map_path = os.path.join(comm_dir, 'sources_map.json')
       mode = 'w' if PY3 else 'wb'
       with open(sources_map_path, mode) as fp:
         json.dump(sources_map, fp)
 
       renaming_args = [
-        '--pants-rootdir-comm-path', rootdir_comm_path,
         '--pants-sources-map-path', sources_map_path
       ]
 
-      yield renaming_args + self._get_sharding_args(), get_pytest_rootdir
+      yield renaming_args + self._get_sharding_args()
 
   @contextmanager
   def _test_runner(self, workdirs, test_targets, sources_map):
     pytest_binary = self.context.products.get_data(PytestPrep.PytestBinary)
-    with self._pants_pytest_plugin_args(sources_map) as (plugin_args, get_pytest_rootdir):
+    with self._pants_pytest_plugin_args(sources_map) as plugin_args:
       with self._maybe_emit_coverage_data(workdirs,
                                           test_targets,
                                           pytest_binary.pex) as coverage_args:
-        yield (pytest_binary,
-               ['-p', pytest_binary.pytest_plugin_module] + plugin_args + coverage_args,
-               get_pytest_rootdir)
+        pytest_rootdir = get_buildroot()
+        yield (
+          pytest_binary,
+          [
+            '--rootdir', pytest_rootdir,
+            '-p', pytest_binary.pytest_plugin_module
+          ] + plugin_args + coverage_args,
+          pytest_rootdir
+        )
 
   def _constrain_pytest_interpreter_search_path(self):
     """Return an environment for invoking a pex which ensures the use of the selected interpreter.
@@ -427,11 +426,11 @@ def _do_run_tests_with_args(self, pex, args):
     try:
       env = dict(os.environ)
 
-      # Ensure we don't leak source files or undeclared 3rdparty requirements into the py.test PEX
+      # Ensure we don't leak source files or undeclared 3rdparty requirements into the pytest PEX
       # environment.
       pythonpath = env.pop('PYTHONPATH', None)
       if pythonpath:
-        self.context.log.warn('scrubbed PYTHONPATH={} from py.test environment'.format(pythonpath))
+        self.context.log.warn('scrubbed PYTHONPATH={} from pytest environment'.format(pythonpath))
       # But allow this back door for users who do want to force something onto the test pythonpath,
       # e.g., modules required during a debugging session.
       extra_pythonpath = self.get_options().extra_pythonpath
@@ -502,9 +501,9 @@ def _get_failed_targets_from_junitxml(self, junitxml, targets, pytest_rootdir):
           test_failed = testcase.getElementsByTagName('failure')
           test_errored = testcase.getElementsByTagName('error')
           if test_failed or test_errored:
-            # The file attribute is always relative to the py.test rootdir.
+            # The file attribute is always relative to the pytest rootdir.
             pytest_relpath = testcase.getAttribute('file')
-            relsrc = os.path.join(buildroot_relpath, pytest_relpath)
+            relsrc = os.path.normpath(os.path.join(buildroot_relpath, pytest_relpath))
             failed_target = relsrc_to_target.get(relsrc)
             if failed_target:
               failed_targets.add(failed_target)
@@ -521,7 +520,7 @@ def _get_target_from_test(self, test_info, targets, pytest_rootdir):
     relsrc_to_target = self._map_relsrc_to_targets(targets)
     buildroot_relpath = os.path.relpath(pytest_rootdir, get_buildroot())
     pytest_relpath = test_info['file']
-    relsrc = os.path.join(buildroot_relpath, pytest_relpath)
+    relsrc = os.path.normpath(os.path.join(buildroot_relpath, pytest_relpath))
     return relsrc_to_target.get(relsrc)
 
   @contextmanager
@@ -610,7 +609,7 @@ def _run_pytest(self, fail_fast, test_targets, workdirs):
 
     with self._test_runner(workdirs, test_targets, sources_map) as (pytest_binary,
                                                                     test_args,
-                                                                    get_pytest_rootdir):
+                                                                    pytest_rootdir):
       # Validate that the user didn't provide any passthru args that conflict
       # with those we must set ourselves.
       for arg in self.get_passthru_args():
@@ -622,7 +621,8 @@ def _run_pytest(self, fail_fast, test_targets, workdirs):
       # N.B. the `--confcutdir` here instructs pytest to stop scanning for conftest.py files at the
       # top of the buildroot. This prevents conftest.py files from outside (e.g. in users home dirs)
       # from leaking into pants test runs. See: https://github.com/pantsbuild/pants/issues/2726
-      args = ['-c', pytest_binary.config_path,
+      args = ['-c', os.devnull,  # Force an empty pytest.ini
+              '-o' 'cache_dir={}'.format(os.path.join(self.workdir, '.pytest_cache')),
               '--junitxml', junitxml_path,
               '--confcutdir', get_buildroot(),
               '--continue-on-collection-errors']
@@ -654,7 +654,6 @@ def _run_pytest(self, fail_fast, test_targets, workdirs):
       if not os.path.exists(junitxml_path):
         return result
 
-      pytest_rootdir = get_pytest_rootdir()
       failed_targets = self._get_failed_targets_from_junitxml(junitxml_path,
                                                               test_targets,
                                                               pytest_rootdir)