Bug 1318200 - Filter Stylo platforms when Servo isn't available; r=dustin

Stylo automation doesn't work unless Servo is present in the source
directory. This commit introduces a "check_servo" filter that prunes
tasks requiring Servo. Currently, this is implemented as a test against
platforms that are unique to Servo.

The use of relative path checking to find the topsrcdir is a bit
unfortunate. But we use this pattern elsewhere in this code.

MozReview-Commit-ID: IRtd53tudJW

--HG--
extra : rebase_source : 8c4742c13878d762fe7970eedfa5937fdaebe8c4

taskcluster/taskgraph/decision.py

@@ -131,6 +131,7 @@ def get_decision_parameters(options):
     # Define default filter list, as most configurations shouldn't need
     # custom filters.
     parameters['filters'] = [
+        'check_servo',
         'target_tasks_method',
     ]
 

taskcluster/taskgraph/filter_tasks.py

@@ -4,10 +4,16 @@
 
 from __future__ import absolute_import, unicode_literals
 
+import logging
+import os
+
 from . import (
     target_tasks,
 )
 
+logger = logging.getLogger(__name__)
+
+GECKO = os.path.realpath(os.path.join(os.path.dirname(__file__), '..', '..'))
 
 filter_task_functions = {}
 
@@ -30,3 +36,24 @@ def filter_target_tasks(graph, parameters):
     attr = parameters.get('target_tasks_method', 'all_tasks')
     fn = target_tasks.get_method(attr)
     return fn(graph, parameters)
+
+
+@filter_task('check_servo')
+def filter_servo(graph, parameters):
+    """Filters out tasks requiring Servo if Servo isn't present."""
+    if os.path.exists(os.path.join(GECKO, 'servo')):
+        return graph.tasks.keys()
+
+    logger.info('servo/ directory not present; removing tasks requiring it')
+
+    SERVO_PLATFORMS = {
+        'linux64-stylo',
+    }
+
+    def fltr(task):
+        if task.attributes.get('build_platform') in SERVO_PLATFORMS:
+            return False
+
+        return True
+
+    return [l for l, t in graph.tasks.iteritems() if fltr(t)]

taskcluster/taskgraph/test/test_filters.py

@@ -0,0 +1,53 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from __future__ import absolute_import, unicode_literals
+
+import os
+import shutil
+import tempfile
+import unittest
+
+from mozunit import main
+
+from .. import filter_tasks
+from ..graph import (
+    Graph,
+)
+from ..taskgraph import (
+    TaskGraph,
+)
+from .util import (
+    TestTask,
+)
+
+
+class TestServoFilter(unittest.TestCase):
+    def setUp(self):
+        self._tmpdir = tempfile.mkdtemp()
+        filter_tasks.GECKO = self._tmpdir
+
+    def tearDown(self):
+        shutil.rmtree(self._tmpdir)
+
+    def test_basic(self):
+        graph = TaskGraph(tasks={
+            'a': TestTask(kind='build', label='a',
+                          attributes={'build_platform': 'linux64'}),
+            'b': TestTask(kind='build', label='b',
+                          attributes={'build_platform': 'linux64-stylo'}),
+            'c': TestTask(kind='desktop-test', label='c', attributes={}),
+        }, graph=Graph(nodes={'a', 'b', 'c'}, edges=set()))
+
+        # Missing servo/ directory should prune tasks requiring Servo.
+        self.assertEqual(set(filter_tasks.filter_servo(graph, {})), {'a', 'c'})
+
+        # Servo tasks should be retained if servo/ present.
+        os.mkdir(os.path.join(self._tmpdir, 'servo'))
+        self.assertEqual(set(filter_tasks.filter_servo(graph, {})),
+                         {'a', 'b', 'c'})
+
+
+if __name__ == '__main__':
+    main()