Don't special-case python dists in resolve_requirements(). (#5483)

Since we now synthesize PythonRequirementLibrary targets for
each local dist, there's no need to handle them specially.

Also ensures that we always create a requirements product, even
for an empty set of requirements, so that downstream tasks
don't have to check for this case.  Removes a test that actually
verified that the opposite was true, for some reason...

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

@@ -5,7 +5,7 @@
 from __future__ import (absolute_import, division, generators, nested_scopes, print_function,
                         unicode_literals, with_statement)
 
-from pants.backend.python.tasks.pex_build_util import has_python_requirements, is_local_python_dist
+from pants.backend.python.tasks.pex_build_util import has_python_requirements
 from pants.backend.python.tasks.resolve_requirements_task_base import ResolveRequirementsTaskBase
 
 
@@ -18,8 +18,5 @@ def product_types(cls):
     return [cls.REQUIREMENTS_PEX]
 
   def execute(self):
-    req_libs = self.context.targets(has_python_requirements)
-    dist_tgts = self.context.targets(is_local_python_dist)
-    if req_libs or dist_tgts:
-      pex = self.resolve_requirements(req_libs, dist_tgts)
-      self.context.products.register_data(self.REQUIREMENTS_PEX, pex)
+    pex = self.resolve_requirements(self.context.targets(has_python_requirements))
+    self.context.products.register_data(self.REQUIREMENTS_PEX, pex)

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

@@ -33,17 +33,13 @@ def prepare(cls, options, round_manager):
     round_manager.require_data(PythonInterpreter)
     round_manager.optional_product(PythonRequirementLibrary)  # For local dists.
 
-  def resolve_requirements(self, req_libs, local_dist_targets=None):
+  def resolve_requirements(self, req_libs):
     """Requirements resolution for PEX files.
 
     :param req_libs: A list of :class:`PythonRequirementLibrary` targets to resolve.
-    :param local_dist_targets: A list of :class:`PythonDistribution` targets to resolve.
     :returns: a PEX containing target requirements and any specified python dist targets.
     """
-    tgts = req_libs
-    if local_dist_targets:
-      tgts = req_libs + local_dist_targets
-    with self.invalidated(tgts) as invalidation_check:
+    with self.invalidated(req_libs) as invalidation_check:
       # If there are no relevant targets, we still go through the motions of resolving
       # an empty set of requirements, to prevent downstream tasks from having to check
       # for this special case.

tests/python/pants_test/backend/python/tasks/test_resolve_requirements.py

@@ -26,11 +26,6 @@ class ResolveRequirementsTest(TaskTestBase):
   def task_type(cls):
     return ResolveRequirements
 
-  def test_resolve_no_targets(self):
-    empty_tgt = self.make_target(spec=':empty')
-    pex = self._resolve_requirements([empty_tgt])
-    self.assertTrue(pex is None)
-
   def test_resolve_simple_requirements(self):
     noreqs_tgt = self._fake_target('noreqs', [])
     ansicolors_tgt = self._fake_target('ansicolors', ['ansicolors==1.0.2'])