Bug 1403342 - default to -j none and do not optimize_target_tasks for try; r=ahal

With this in place, all `-j`obs will not run by default on try.  This will omit
such jobs in most try pushes even if files-changed matches. This is
unfortunate, but better than running them unconditionally.  Fuzzy selections,
and later `just try it` pushes, are the ultimate solution here.

With this change, a push with no try syntax or try_task_config.json will schedule
no tasks at all.

MozReview-Commit-ID: FGjqlDW1FT6

--HG--
extra : rebase_source : 727ceafb1b6d24f83c0c7382b6a877ecb65863ab

taskcluster/docs/try.rst

@@ -13,7 +13,8 @@ integration branches are at SCM level 3.
 Scheduling a Task on Try
 ------------------------
 
-There are two methods for scheduling a task on try.
+There are three methods for scheduling a task on try: legacy try option syntax,
+try task config, and an empty try.
 
 Try Option Syntax
 :::::::::::::::::
@@ -132,6 +133,14 @@ It looks like this:
 
 See the `existing templates`_ for examples.
 
+Empty Try
+:::::::::
+
+If there is no try syntax or ``try_task_config.json``, the ``try_mode``
+parameter is None and no tasks are selected to run.  The resulting push will
+only have a decision task, but one with an "add jobs" action that can be used
+to add the desired jobs to the try push.
+
 .. _tryselect: https://dxr.mozilla.org/mozilla-central/source/tools/tryselect
 .. _JSON-e: https://taskcluster.github.io/json-e/
 .. _taskgraph module: https://dxr.mozilla.org/mozilla-central/source/taskcluster/taskgraph/templates

taskcluster/taskgraph/decision.py

@@ -215,11 +215,7 @@ def get_decision_parameters(options):
         else:
             parameters['try_options'] = None
 
-        if parameters['try_mode'] == 'try_option_syntax':
-            # Try option syntax is imprecise, so optimize away tasks even if they
-            # are selected by the syntax.
-            parameters['optimize_target_tasks'] = True
-        elif parameters['try_mode'] == 'try_task_config':
+        if parameters['try_mode']:
             # The user has explicitly requested a set of jobs, so run them all
             # regardless of optimization.  Their dependencies can be optimized,
             # though.

taskcluster/taskgraph/target_tasks.py

@@ -110,11 +110,9 @@ def target_tasks_try(full_task_graph, parameters):
     elif try_mode == 'try_option_syntax':
         return _try_option_syntax(full_task_graph, parameters)
     else:
-        # With no try mode, we would like to schedule everything (following
-        # run_on_projects) and let optimization trim it down.  But optimization
-        # isn't yet up to the task, so instead we use try_option_syntax with
-        # an empty message (which basically just schedules `-j`objs)
-        return _try_option_syntax(full_task_graph, parameters)
+        # With no try mode, we schedule nothing, allowing the user to add tasks
+        # later via treeherder.
+        return []
 
 
 @_target_task('default')

taskcluster/taskgraph/test/test_target_tasks.py

@@ -84,16 +84,17 @@ class TestTargetTasks(unittest.TestCase):
         finally:
             try_option_syntax.TryOptionSyntax = orig_TryOptionSyntax
 
-    def test_just_try_it(self):
-        "try_mode = None runs try optoin syntax with no options"
+    def test_empty_try(self):
+        "try_mode = None runs nothing"
         tg = self.make_task_graph()
         method = target_tasks.get_method('try_tasks')
-        with self.fake_TryOptionSyntax():
-            params = {
-                'try_mode': None,
-                'message': '',
-            }
-            self.assertEqual(method(tg, params), ['b'])
+        params = {
+            'try_mode': None,
+            'project': 'try',
+            'message': '',
+        }
+        # only runs the task with run_on_projects: try
+        self.assertEqual(method(tg, params), [])
 
     def test_try_option_syntax(self):
         "try_mode = try_option_syntax uses TryOptionSyntax"

taskcluster/taskgraph/test/test_try_option_syntax.py

@@ -69,7 +69,7 @@ class TestTryOptionSyntax(unittest.TestCase):
         tos = TryOptionSyntax(parameters, graph_with_jobs)
         # equilvant to "try:"..
         self.assertEqual(tos.build_types, [])
-        self.assertEqual(tos.jobs, None)
+        self.assertEqual(tos.jobs, [])
 
     def test_apostrophe_in_message(self):
         "apostrophe does not break parsing"

taskcluster/taskgraph/try_option_syntax.py

@@ -323,7 +323,9 @@ class TryOptionSyntax(object):
         self.include_nightly = options['include_nightly']
 
     def parse_jobs(self, jobs_arg):
-        if not jobs_arg or jobs_arg == ['all']:
+        if not jobs_arg or jobs_arg == ['none']:
+            return []  # default is `-j none`
+        if jobs_arg == ['all']:
             return None
         expanded = []
         for job in jobs_arg:
@@ -597,23 +599,17 @@ class TryOptionSyntax(object):
             else:
                 return False
 
-        job_try_name = attr('job_try_name')
-        if job_try_name:
+        if attr('job_try_name'):
             # Beware the subtle distinction between [] and None for self.jobs and self.platforms.
             # They will be [] if there was no try syntax, and None if try syntax was detected but
             # they remained unspecified.
-            if self.jobs:
-                return job_try_name in self.jobs
-            elif not self.jobs and 'build' in task.dependencies:
-                # We exclude tasks with build dependencies from the default set of jobs because
-                # they will schedule their builds even if they end up optimized away. This means
-                # to run these tasks on try, they'll need to be explicitly specified by -j until
-                # we find a better solution (see bug 1372510).
-                return False
-            elif not self.jobs and attr('build_platform'):
-                if self.platforms is None or attr('build_platform') in self.platforms:
-                    return True
-                return False
+            if self.jobs is not None:
+                return attr('job_try_name') in self.jobs
+
+            # User specified `-j all`
+            if self.platforms is not None and attr('build_platform') not in self.platforms:
+                return False  # honor -p for jobs governed by a platform
+            # "all" means "everything with `try` in run_on_projects"
             return check_run_on_projects()
         elif attr('kind') == 'test':
             return match_test(self.unittests, 'unittest_try_name') \