Allow tasks to opt-in to target filtering (#7283)

Followup to #7275 following [discussion](#7275 (comment)) that the target filter was being applied to tasks that do not support it (e.g. tasks that don't access targets via `get_targets()`)

This adds a class property to `Task` that allows subclasses to effectively opt-in to the new behavior - and sets that flag to `True` for `fmt` and `lint` tasks.

src/python/pants/task/fmt_task_mixin.py

@@ -11,3 +11,4 @@
 class FmtTaskMixin(HasSkipAndTransitiveGoalOptionsMixin):
   """A mixin to combine with code formatting tasks."""
   goal_options_registrar_cls = SkipAndTransitiveGoalOptionsRegistrar
+  target_filtering_enabled = True

src/python/pants/task/lint_task_mixin.py

@@ -11,3 +11,4 @@
 class LintTaskMixin(HasSkipAndTransitiveGoalOptionsMixin):
   """A mixin to combine with lint tasks."""
   goal_options_registrar_cls = SkipAndTransitiveGoalOptionsRegistrar
+  target_filtering_enabled = True

src/python/pants/task/task.py

@@ -30,7 +30,7 @@
 from pants.subsystem.subsystem_client_mixin import SubsystemClientMixin
 from pants.util.dirutil import safe_mkdir, safe_rm_oldest_items_in_dir
 from pants.util.memo import memoized_method, memoized_property
-from pants.util.meta import AbstractClass
+from pants.util.meta import AbstractClass, classproperty
 
 
 class TaskBase(SubsystemClientMixin, Optionable, AbstractClass):
@@ -97,7 +97,8 @@ def _compute_stable_name(cls):
   @classmethod
   def subsystem_dependencies(cls):
     return (super(TaskBase, cls).subsystem_dependencies() +
-            (CacheSetup.scoped(cls), TargetFilter.scoped(cls), BuildInvalidator.Factory, SourceRootConfig))
+            (CacheSetup.scoped(cls), BuildInvalidator.Factory, SourceRootConfig) +
+            ((TargetFilter.scoped(cls),) if cls.target_filtering_enabled else tuple()))
 
   @classmethod
   def product_types(cls):
@@ -223,6 +224,17 @@ def act_transitively(self):
     """
     return True
 
+  @classproperty
+  def target_filtering_enabled(cls):
+    """Whether this task should apply configured filters against targets.
+
+    Tasks can override to enable target filtering (e.g. based on tags) and must
+    access targets via get_targets()
+
+    :API: public
+    """
+    return False
+
   def get_targets(self, predicate=None):
     """Returns the candidate targets this task should act on.
 
@@ -241,8 +253,14 @@ def get_targets(self, predicate=None):
     initial_targets = (self.context.targets(predicate) if self.act_transitively
                        else list(filter(predicate, self.context.target_roots)))
 
-    included_targets = TargetFilter.scoped_instance(self).apply(initial_targets)
-    excluded_targets = set(initial_targets).difference(included_targets)
+    if not self.target_filtering_enabled:
+      return initial_targets
+    else: 
+      return self._filter_targets(initial_targets)
+
+  def _filter_targets(self, targets):
+    included_targets = TargetFilter.scoped_instance(self).apply(targets)
+    excluded_targets = set(targets).difference(included_targets)
 
     if excluded_targets:
       self.context.log.info("{} target(s) excluded".format(len(excluded_targets)))

tests/python/pants_test/build_graph/test_target_filter_subsystem.py

@@ -15,6 +15,7 @@ class TestTargetFilter(TaskTestBase):
 
   class DummyTask(Task):
     options_scope = 'dummy'
+    target_filtering_enabled = True
 
     def execute(self):
       self.context.products.safe_create_data('task_targets', self.get_targets)

tests/python/pants_test/task/test_task.py

@@ -13,6 +13,7 @@
 from pants.base.exceptions import TaskError
 from pants.build_graph.build_file_aliases import BuildFileAliases
 from pants.build_graph.files import Files
+from pants.build_graph.target_filter_subsystem import TargetFilter
 from pants.cache.cache_setup import CacheSetup
 from pants.option.arg_splitter import GLOBAL_SCOPE
 from pants.subsystem.subsystem import Subsystem
@@ -149,6 +150,11 @@ def execute(self):
     pass
 
 
+class TaskWithTargetFiltering(DummyTask):
+  options_scope = 'task-with-target-filtering'
+  target_filtering_enabled = True
+
+
 class TaskTest(TaskTestBase):
 
   _filename = 'f'
@@ -650,3 +656,9 @@ def test_fingerprint_transitive(self):
     fp3 = self._synth_fp(cls=TaskWithTransitiveSubsystemDependencies,
                          options_fingerprintable=option_spec)
     self.assertNotEqual(fp1, fp3)
+
+  def test_target_filtering_enabled(self):
+    self.assertNotIn(TargetFilter.scoped(DummyTask),
+                     DummyTask.subsystem_dependencies())
+    self.assertIn(TargetFilter.scoped(TaskWithTargetFiltering), 
+                  TaskWithTargetFiltering.subsystem_dependencies())