Tighten PytestRun coverage plugin.

src/python/pants/backend/python/__init__.py

@@ -1 +0,0 @@
-__import__('pkg_resources').declare_namespace(__name__)

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

@@ -1 +0,0 @@
-__import__('pkg_resources').declare_namespace(__name__)

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

@@ -15,20 +15,18 @@
 from coverage.python import PythonFileReporter
 
 
-class MyFileTracer(FileTracer):
+class SimpleFileTracer(FileTracer):
   def __init__(self, filename):
-    super(MyFileTracer, self).__init__()
+    super(SimpleFileTracer, self).__init__()
     self._filename = filename
 
   def source_filename(self):
     return self._filename
 
 
-class MyFileReporter(PythonFileReporter):
-  """A python file reporter that knows how to map Pants PEX chroots back to repo source code."""
-
+class SimpleFileReporter(PythonFileReporter):
   def __init__(self, morf, relpath):
-    super(MyFileReporter, self).__init__(morf, coverage=None)
+    super(SimpleFileReporter, self).__init__(morf, coverage=None)
     self._relpath = relpath
 
   def relative_filename(self):
@@ -50,11 +48,11 @@ def no_branch_lines(self):
                                       join_regex(DEFAULT_PARTIAL_ALWAYS[:]))
 
 
-class MyPlugin(CoveragePlugin):
+class ChrootRemappingPlugin(CoveragePlugin):
   """A plugin that knows how to map Pants PEX chroots back to repo source code when reporting."""
 
   def __init__(self, buildroot, src_chroot_path, src_to_target_base):
-    super(MyPlugin, self).__init__()
+    super(ChrootRemappingPlugin, self).__init__()
     self._buildroot = buildroot
     self._src_chroot_path = src_chroot_path
     self._src_to_target_base = src_to_target_base
@@ -68,14 +66,15 @@ def find_executable_files(self, top):
             yield os.path.join(root, f)
 
   def file_tracer(self, filename):
+    # Don't trace third party libraries or the standard lib, just user code in the src chroot.
     if filename.startswith(self._src_chroot_path):
       src = os.path.relpath(filename, self._src_chroot_path)
       if src in self._src_to_target_base:
-        return MyFileTracer(filename)
+        return SimpleFileTracer(filename)
 
   def file_reporter(self, filename):
     mapped_relpath = self._map_relpath(filename)
-    return MyFileReporter(filename, mapped_relpath or filename)
+    return SimpleFileReporter(filename, mapped_relpath)
 
   def _map_relpath(self, filename):
     src = os.path.relpath(filename, self._src_chroot_path)
@@ -92,4 +91,4 @@ def coverage_init(reg, options):
   buildroot = options['buildroot']
   src_chroot_path = options['src_chroot_path']
   src_to_target_base = json.loads(options['src_to_target_base'])
-  reg.add_file_tracer(MyPlugin(buildroot, src_chroot_path, src_to_target_base))
+  reg.add_file_tracer(ChrootRemappingPlugin(buildroot, src_chroot_path, src_to_target_base))

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

@@ -20,6 +20,8 @@ class PytestPrep(PythonExecutionTaskBase):
   class PytestBinary(object):
     """A `py.test` PEX binary with an embedded default (empty) `pytest.ini` config file."""
 
+    _COVERAGE_PLUGIN_MODULE_NAME = '__{}__'.format(__name__.replace('.', '_'))
+
     def __init__(self, pex):
       self._pex = pex
 
@@ -39,9 +41,17 @@ def config_path(self):
       """
       return os.path.join(self._pex.path(), 'pytest.ini')
 
+    @classmethod
+    def coverage_plugin_module(cls):
+      """Return the name of the coverage plugin module embedded in this py.test binary.
+
+      :rtype: str
+      """
+      return cls._COVERAGE_PLUGIN_MODULE_NAME
+
   @classmethod
   def implementation_version(cls):
-    return super(PytestPrep, cls).implementation_version() + [('PytestPrep', 1)]
+    return super(PytestPrep, cls).implementation_version() + [('PytestPrep', 2)]
 
   @classmethod
   def product_types(cls):
@@ -56,10 +66,7 @@ def extra_requirements(self):
 
   def extra_files(self):
     yield self.ExtraFile.empty('pytest.ini')
-
-    enclosing_dir = os.path.dirname(__name__.replace('.', os.sep))
-    plugin_path = os.path.join(enclosing_dir, 'coverage/plugin.py')
-    yield self.ExtraFile(path=plugin_path,
+    yield self.ExtraFile(path='{}.py'.format(self.PytestBinary.coverage_plugin_module()),
                          content=pkg_resources.resource_string(__name__, 'coverage/plugin.py'))
 
   def execute(self):

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

@@ -186,7 +186,7 @@ def _ensure_section(cp, section):
   def _add_plugin_config(cls, cp, src_chroot_path, src_to_target_base):
     # We use a coverage plugin to map PEX chroot source paths back to their original repo paths for
     # report output.
-    plugin_module = 'pants.backend.python.tasks.coverage.plugin'
+    plugin_module = PytestPrep.PytestBinary.coverage_plugin_module()
     cls._ensure_section(cp, 'run')
     cp.set('run', 'plugins', plugin_module)