Expand local_dir in Trial init (ray-project#2013)

* Fix the case where Trial logs into wrong paths when `local_dir`
argument starts with tilde (~), by expanding the `local_dir` argument
* Add test case for checking that the tilde gets expanded

python/ray/tune/test/trial_runner_test.py

@@ -161,6 +161,26 @@ def train(config, reporter):
             }
         })
 
+    def testLogdirStartingWithTilde(self):
+        local_dir = '~/ray_results/local_dir'
+
+        def train(config, reporter):
+            cwd = os.getcwd()
+            assert cwd.startswith(os.path.expanduser(local_dir)), cwd
+            assert not cwd.startswith('~'), cwd
+            reporter(timesteps_total=1)
+
+        register_trainable('f1', train)
+        run_experiments({
+            'foo': {
+                'run': 'f1',
+                'local_dir': local_dir,
+                'config': {
+                    'a': 'b'
+                },
+            }
+        })
+
     def testLongFilename(self):
         def train(config, reporter):
             assert "/tmp/logdir/foo" in os.getcwd(), os.getcwd()

python/ray/tune/trial.py

@@ -110,7 +110,7 @@ def __init__(self,
         # Trial config
         self.trainable_name = trainable_name
         self.config = config or {}
-        self.local_dir = local_dir
+        self.local_dir = os.path.expanduser(local_dir)
         self.experiment_tag = experiment_tag
         self.resources = (
             resources