[tune] Prevent leak of magic keys in trial config (#9903)

Co-authored-by: Kai Fricke <kai@anyscale.com>
Co-authored-by: Richard Liaw <rliaw@berkeley.edu>

python/ray/tune/experiment.py

@@ -1,6 +1,7 @@
 import copy
 import logging
 import os
+from typing import Sequence
 
 from ray.tune.error import TuneError
 from ray.tune.function_runner import detect_checkpoint_function
@@ -45,6 +46,31 @@ def _raise_on_durable(trainable_name, sync_to_driver, upload_dir):
                 "`upload_dir` must be provided.")
 
 
+def _validate_log_to_file(log_to_file):
+    """Validate ``tune.run``'s ``log_to_file`` parameter. Return
+    validated relative stdout and stderr filenames."""
+    if not log_to_file:
+        stdout_file = stderr_file = None
+    elif isinstance(log_to_file, bool) and log_to_file:
+        stdout_file = "stdout"
+        stderr_file = "stderr"
+    elif isinstance(log_to_file, str):
+        stdout_file = stderr_file = log_to_file
+    elif isinstance(log_to_file, Sequence):
+        if len(log_to_file) != 2:
+            raise ValueError(
+                "If you pass a Sequence to `log_to_file` it has to have "
+                "a length of 2 (for stdout and stderr, respectively). The "
+                "Sequence you passed has length {}.".format(len(log_to_file)))
+        stdout_file, stderr_file = log_to_file
+    else:
+        raise ValueError(
+            "You can pass a boolean, a string, or a Sequence of length 2 to "
+            "`log_to_file`, but you passed something else ({}).".format(
+                type(log_to_file)))
+    return stdout_file, stderr_file
+
+
 class Experiment:
     """Tracks experiment specifications.
 
@@ -82,6 +108,7 @@ class Experiment:
                  upload_dir=None,
                  trial_name_creator=None,
                  loggers=None,
+                 log_to_file=False,
                  sync_to_driver=None,
                  checkpoint_freq=0,
                  checkpoint_at_end=False,
@@ -133,6 +160,8 @@ class Experiment:
 
         _raise_on_durable(self._run_identifier, sync_to_driver, upload_dir)
 
+        stdout_file, stderr_file = _validate_log_to_file(log_to_file)
+
         spec = {
             "run": self._run_identifier,
             "stop": stopping_criteria,
@@ -145,6 +174,7 @@ class Experiment:
             "remote_checkpoint_dir": self.remote_checkpoint_dir,
             "trial_name_creator": trial_name_creator,
             "loggers": loggers,
+            "log_to_file": (stdout_file, stderr_file),
             "sync_to_driver": sync_to_driver,
             "checkpoint_freq": checkpoint_freq,
             "checkpoint_at_end": checkpoint_at_end,