build: add recipe code for new autoroller

scripts/slave/recipe_modules/recipe_autoroller/api.py

+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+from recipe_engine import recipe_api
+
+
+class RecipeAutorollerApi(recipe_api.RecipeApi):
+  def prepare_checkout(self):

[martiniss, 2016/04/07 18:27:59]

Why do we need this exactly?

[Paweł Hajdan Jr., 2016/04/07 20:32:15]

So that this logic is not duplicated between public and internal recipes.

If you have specific suggestion how to structure the code differently, feel free
to share.

[martiniss, 2016/04/07 21:27:12]

I guess my question was more existential; I don't see why we need this checkout
exactly. But we're duplicating what we have already, so it looks fine to me.

+    """Creates a default checkout for the recipe autoroller."""
+    self.m.gclient.set_config('recipes_py')
+    self.m.gclient.checkout()
+    self.m.gclient.runhooks()
+
+  def roll_projects(self, projects):
+    """Attempts to roll each project from the provided list.
+
+    If rolling any of the projects leads to failures, other
+    projects are not affected.
+    """
+    project_data = self.m.luci_config.get_projects()
+    with recipe_api.defer_results():
+      for project in projects:
+        with self.m.step.nest(str(project)):
+          self._roll_project(project_data[project])
+
+  def _roll_project(self, project_data):
+    with self.m.tempfile.temp_dir('roll_%s' % project_data['id']) as workdir:
+      self.m.git.checkout(
+          project_data['repo_url'], dir_path=workdir, submodules=False)
+
+      recipes_cfg_path = workdir.join('infra', 'config', 'recipes.cfg')
+
+      roll_step = self.m.python('roll',
+          self.m.path['checkout'].join('recipes-py', 'recipes.py'),
+          ['--package', recipes_cfg_path, 'autoroll',
+           '--output-json', self.m.json.output()])
+      roll_result = roll_step.json.output
+
+      if roll_result['success']:
+        blame = []
+        for project, commits in roll_result[
+            'picked_roll_details']['commit_infos'].iteritems():
+          blame.append('%s:' % project)
+          for commit in commits:
+            message = commit['message'].splitlines()
+            # TODO(phajdan): truncate long messages.
+            message = message[0] if message else 'n/a'
+            # TODO(phajdan): get clickable links for the commits.
+            blame.append('  %s %s (%s)' % (
+                commit['revision'], message, commit['author']))
+        roll_step.presentation.logs['blame'] = blame
+
+        if roll_result['trivial']:
+          roll_step.presentation.step_text += ' (trivial)'
+        else:
+          roll_step.presentation.status = self.m.step.WARNING
+      else:
+        if (not roll_result['roll_details'] and
+            not roll_result['rejected_candidates_details']):
+          roll_step.presentation.step_text += ' (already at latest revisions)'
+        else:
+          roll_step.presentation.status = self.m.step.FAILURE
+
+      # TODO(phajdan): upload the CL.
+      self.m.git('diff', 'HEAD', cwd=workdir)