More accurate reported runtime when pantsd is in use. (#14177)

The `PantsLoader` captures a `start_time` as early as possible, which is then supposed to be propagated all the way to the `pantsd` server via environment variables. But the `RemotePantsRunner` was calculating its own start time, which would miss out on some of the startup costs (options parsing in particular).

[ci skip-rust]
[ci skip-build-wheels]

src/python/pants/bin/daemon_pants_runner.py

@@ -113,6 +113,12 @@ def single_daemonized_run(
             # Capture the client's start time, which we propagate here in order to get an accurate
             # view of total time.
             env_start_time = env.get("PANTSD_RUNTRACKER_CLIENT_START_TIME", None)
+            if not env_start_time:
+                # NB: We warn rather than erroring here because it eases use of non-Pants nailgun
+                # clients for testing.
+                logger.warning(
+                    "No start time was reported by the client! Metrics may be inaccurate."
+                )
             start_time = float(env_start_time) if env_start_time else time.time()
 
             options_bootstrapper = OptionsBootstrapper.create(

src/python/pants/bin/pants_runner.py

@@ -83,7 +83,7 @@ def run(self, start_time: float) -> ExitCode:
             if self._should_run_with_pantsd(global_bootstrap_options):
                 try:
                     remote_runner = RemotePantsRunner(self.args, self.env, options_bootstrapper)
-                    return remote_runner.run()
+                    return remote_runner.run(start_time)
                 except RemotePantsRunner.Fallback as e:
                     logger.warning(f"Client exception: {e!r}, falling back to non-daemon mode")
 

src/python/pants/bin/remote_pants_runner.py

@@ -101,23 +101,24 @@ def __init__(
         :param env: The environment (e.g. os.environ) for this run.
         :param options_bootstrapper: The bootstrap options.
         """
-        self._start_time = time.time()
         self._args = args
         self._env = env
         self._options_bootstrapper = options_bootstrapper
         self._bootstrap_options = options_bootstrapper.bootstrap_options
         self._client = PantsDaemonClient(self._bootstrap_options)
 
-    def run(self) -> ExitCode:
+    def run(self, start_time: float) -> ExitCode:
         """Starts up a pantsd instance if one is not already running, then connects to it via
         nailgun."""
 
         pantsd_handle = self._client.maybe_launch()
         logger.debug(f"Connecting to pantsd on port {pantsd_handle.port}")
 
-        return self._connect_and_execute(pantsd_handle)
+        return self._connect_and_execute(pantsd_handle, start_time)
 
-    def _connect_and_execute(self, pantsd_handle: PantsDaemonClient.Handle) -> ExitCode:
+    def _connect_and_execute(
+        self, pantsd_handle: PantsDaemonClient.Handle, start_time: float
+    ) -> ExitCode:
         global_options = self._bootstrap_options.for_global_scope()
         executor = GlobalOptions.create_py_executor(global_options)
 
@@ -126,7 +127,7 @@ def _connect_and_execute(self, pantsd_handle: PantsDaemonClient.Handle) -> ExitC
         modified_env = {
             **self._env,
             **ng_env,
-            "PANTSD_RUNTRACKER_CLIENT_START_TIME": str(self._start_time),
+            "PANTSD_RUNTRACKER_CLIENT_START_TIME": str(start_time),
             "PANTSD_REQUEST_TIMEOUT_LIMIT": str(
                 global_options.pantsd_timeout_when_multiple_invocations
             ),