Make requirements on codegen products optional.

src/python/pants/backend/jvm/tasks/coursier_resolve.py

@@ -661,8 +661,10 @@ def product_types(cls):
   @classmethod
   def prepare(cls, options, round_manager):
     super(CoursierResolve, cls).prepare(options, round_manager)
-    round_manager.require_data('java')
-    round_manager.require_data('scala')
+    # Codegen may inject extra resolvable deps, so make sure we have a product dependency
+    # on relevant codegen tasks, if any.
+    round_manager.optional_data('java')
+    round_manager.optional_data('scala')
 
   @classmethod
   def register_options(cls, register):

src/python/pants/backend/jvm/tasks/ivy_resolve.py

@@ -69,8 +69,10 @@ def product_types(cls):
   @classmethod
   def prepare(cls, options, round_manager):
     super(IvyResolve, cls).prepare(options, round_manager)
-    round_manager.require_data('java')
-    round_manager.require_data('scala')
+    # Codegen may inject extra resolvable deps, so make sure we have a product dependency
+    # on relevant codegen tasks, if any.
+    round_manager.optional_data('java')
+    round_manager.optional_data('scala')
 
   def __init__(self, *args, **kwargs):
     super(IvyResolve, self).__init__(*args, **kwargs)

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

@@ -40,7 +40,7 @@ def product_types(cls):
   @classmethod
   def prepare(cls, options, round_manager):
     round_manager.require_data(PythonInterpreter)
-    round_manager.require_data('python')  # For codegen.
+    round_manager.optional_data('python')  # For codegen.
 
   def execute(self):
     targets = self._collect_source_targets()

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

@@ -51,8 +51,9 @@ def cache_target_dirs(self):
 
   @classmethod
   def prepare(cls, options, round_manager):
+    # See comment below for why we don't use the GatherSources.PYTHON_SOURCES product.
     round_manager.require_data(PythonInterpreter)
-    round_manager.require_data('python')  # For codegen.
+    round_manager.optional_data('python')  # For codegen.
     round_manager.optional_product(PythonRequirementLibrary)  # For local dists.
 
   @staticmethod

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

@@ -45,6 +45,9 @@ def _python_native_code_settings(self):
   def prepare(cls, options, round_manager):
     round_manager.require_data(PythonInterpreter)
     round_manager.optional_product(PythonRequirementLibrary)  # For local dists.
+    # Codegen may inject extra resolvable deps, so make sure we have a product dependency
+    # on relevant codegen tasks, if any.
+    round_manager.optional_data('python')
 
   def resolve_requirements(self, interpreter, req_libs):
     """Requirements resolution for PEX files.

src/python/pants/goal/run_tracker.py

@@ -163,6 +163,8 @@ def initialize(self):
       raise AssertionError('RunTracker.initialize must not be called multiple times.')
 
     # Initialize the run.
+
+    # Select a globally unique ID for the run, that sorts by time.
     millis = int((self._run_timestamp * 1000) % 1000)
     run_id = 'pants_run_{}_{}_{}'.format(
       time.strftime('%Y_%m_%d_%H_%M_%S', time.localtime(self._run_timestamp)),

src/python/pants/task/task.py

@@ -535,7 +535,7 @@ def check_artifact_cache(self, vts):
   def do_check_artifact_cache(self, vts, post_process_cached_vts=None):
     """Checks the artifact cache for the specified list of VersionedTargetSets.
 
-    Returns a pair (cached, uncached) of VersionedTargets that were
+    Returns a tuple (cached, uncached, uncached_causes) of VersionedTargets that were
     satisfied/unsatisfied from the cache.
     """
     if not vts: