Fix mb.py swarming retcode

Fixes mb.py always exiting with 0 when running tests on swarming even if
the task failed. This was caused by the switch to the Go version of the
swarming tools, which no longer exit with the task's exit code.

Instead, we need to tell the swarming tool to output JSON and extract
the exit code from that.

Change-Id: If47cbee20e6abf5a1328eb6af1080475fd1d897e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2649346
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Auto-Submit: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#847288}

tools/mb/mb.py

@@ -694,18 +694,26 @@ class MetaBuildWrapper(object):
         return ret
       task_json = self.ReadFile(json_file)
       task_id = json.loads(task_json)["tasks"][0]['task_id']
+      collect_output = self.PathJoin(json_dir, 'collect_output.json')
+      cmd = [
+          self.PathJoin('tools', 'luci-go', 'swarming'),
+          'collect',
+          '-server',
+          swarming_server,
+          '-task-output-stdout=console',
+          '-task-summary-json',
+          collect_output,
+          task_id,
+      ]
+      ret, _, _ = self.Run(cmd, force_verbose=True, buffer_output=False)
+      if ret != 0:
+        return ret
+      collect_json = json.loads(self.ReadFile(collect_output))
+      # The exit_code field is not included if the task was successful.
+      ret = collect_json.get(task_id, {}).get('results', {}).get('exit_code', 0)
     finally:
       if json_dir:
         self.RemoveDirectory(json_dir)
-    cmd = [
-        self.PathJoin('tools', 'luci-go', 'swarming'),
-        'collect',
-        '-server',
-        swarming_server,
-        '-task-output-stdout=console',
-        task_id,
-    ]
-    ret, _, _ = self.Run(cmd, force_verbose=True, buffer_output=False)
     return ret
 
   def _RunLocallyIsolated(self, build_dir, target):

tools/mb/mb_unittest.py

@@ -724,9 +724,11 @@ class UnitTest(unittest.TestCase):
     }
 
     task_json = json.dumps({'tasks': [{'task_id': '00000'}]})
+    collect_json = json.dumps({'00000': {'results': {}}})
 
     mbw = self.fake_mbw(files=files)
     mbw.files[mbw.PathJoin(mbw.TempDir(), 'task.json')] = task_json
+    mbw.files[mbw.PathJoin(mbw.TempDir(), 'collect_output.json')] = collect_json
     original_impl = mbw.ToSrcRelPath
 
     def to_src_rel_path_stub(path):
@@ -740,10 +742,57 @@ class UnitTest(unittest.TestCase):
                 'base_unittests'], mbw=mbw, ret=0)
     mbw = self.fake_mbw(files=files)
     mbw.files[mbw.PathJoin(mbw.TempDir(), 'task.json')] = task_json
+    mbw.files[mbw.PathJoin(mbw.TempDir(), 'collect_output.json')] = collect_json
     mbw.ToSrcRelPath = to_src_rel_path_stub
     self.check(['run', '-s', '-c', 'debug_goma', '-d', 'os', 'Win7',
                 '//out/Default', 'base_unittests'], mbw=mbw, ret=0)
 
+  def test_run_swarmed_task_failure(self):
+    files = {
+        '/fake_src/testing/buildbot/gn_isolate_map.pyl':
+        ("{'base_unittests': {"
+         "  'label': '//base:base_unittests',"
+         "  'type': 'console_test_launcher',"
+         "}}\n"),
+        '/fake_src/out/Default/base_unittests.runtime_deps':
+        ("base_unittests\n"),
+        '/fake_src/out/Default/base_unittests.archive.json':
+        ("{\"base_unittests\":\"fake_hash\"}"),
+        '/fake_src/third_party/depot_tools/cipd_manifest.txt':
+        ("# vpython\n"
+         "/some/vpython/pkg  git_revision:deadbeef\n"),
+    }
+
+    task_json = json.dumps({'tasks': [{'task_id': '00000'}]})
+    collect_json = json.dumps({'00000': {'results': {'exit_code': 1}}})
+
+    mbw = self.fake_mbw(files=files)
+    mbw.files[mbw.PathJoin(mbw.TempDir(), 'task.json')] = task_json
+    mbw.files[mbw.PathJoin(mbw.TempDir(), 'collect_output.json')] = collect_json
+    original_impl = mbw.ToSrcRelPath
+
+    def to_src_rel_path_stub(path):
+      if path.endswith('base_unittests.archive.json'):
+        return 'base_unittests.archive.json'
+      return original_impl(path)
+
+    mbw.ToSrcRelPath = to_src_rel_path_stub
+
+    self.check(
+        ['run', '-s', '-c', 'debug_goma', '//out/Default', 'base_unittests'],
+        mbw=mbw,
+        ret=1)
+    mbw = self.fake_mbw(files=files)
+    mbw.files[mbw.PathJoin(mbw.TempDir(), 'task.json')] = task_json
+    mbw.files[mbw.PathJoin(mbw.TempDir(), 'collect_output.json')] = collect_json
+    mbw.ToSrcRelPath = to_src_rel_path_stub
+    self.check([
+        'run', '-s', '-c', 'debug_goma', '-d', 'os', 'Win7', '//out/Default',
+        'base_unittests'
+    ],
+               mbw=mbw,
+               ret=1)
+
   def test_lookup(self):
     self.check(['lookup', '-c', 'debug_goma'], ret=0,
                out=('\n'