bug 1517909 - format build telemetry time correctly when seconds has no fractional component. r=nalexander

It turns out that Python's `datetime.isoformat` method will leave off the
fractional component of seconds if it would be all zeroes, but the voluptuous
`Datetime` validator wants it to be present, so it's possible to hit an error
if you run mach at exactly an integer second.

This patch switches from `isoformat` to `strftime` with an explicit format
string instead.

Differential Revision: https://phabricator.services.mozilla.com/D15981

--HG--
extra : moz-landing-system : lando

python/mach/mach/test/test_telemetry.py

@@ -154,5 +154,12 @@ def test_registrar_dispatch(run_mach):
     assert d['command'] == 'python'
 
 
+def test_zero_microseconds(run_mach):
+    data = run_mach('python', '--exec-file',
+                    os.path.join(os.path.dirname(__file__), 'zero_microseconds.py'))
+    d = data[0]
+    assert d['command'] == 'python'
+
+
 if __name__ == '__main__':
     mozunit.main()

python/mach/mach/test/zero_microseconds.py

@@ -0,0 +1,14 @@
+# This code is loaded via `mach python --exec-file`, so it runs in the scope of
+# the `mach python` command.
+old = self._mach_context.post_dispatch_handler  # noqa: F821
+
+
+def handler(context, handler, instance, result,
+            start_time, end_time, depth, args):
+    global old
+    # Round off sub-second precision.
+    old(context, handler, instance, result,
+        int(start_time), end_time, depth, args)
+
+
+self._mach_context.post_dispatch_handler = handler  # noqa: F821

python/mozbuild/mozbuild/telemetry.py

@@ -258,8 +258,8 @@ def gather_telemetry(command='', success=False, start_time=None, end_time=None,
     '''
     data = {
         'client_id': get_client_id(mach_context.state_dir),
-        # Simplest way to get an rfc3339 datetime string, AFAICT.
-        'time': datetime.utcfromtimestamp(start_time).isoformat(b'T') + 'Z',
+        # Get an rfc3339 datetime string.
+        'time': datetime.utcfromtimestamp(start_time).strftime('%Y-%m-%dT%H:%M:%S.%fZ'),
         'command': command,
         'argv': filter_args(command, sys.argv, paths),
         'success': success,