[rllib] Allow development without needing to compile Ray (#3623)

* wip

* lint

* wip

* wip

* rename

* wip

* Cleaner handling of cli prompt

python/ray/rllib/setup-rllib-dev.py

@@ -0,0 +1,38 @@
+#!/usr/bin/env python
+"""This script allows you to develop RLlib without needing to compile Ray."""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import click
+import os
+import subprocess
+
+import ray
+
+if __name__ == "__main__":
+    rllib_home = os.path.abspath(os.path.join(ray.__file__, "../rllib"))
+    local_home = os.path.abspath(os.path.dirname(__file__))
+    assert os.path.isdir(rllib_home), rllib_home
+    assert os.path.isdir(local_home), local_home
+    click.confirm(
+        "This will replace:\n  {}\nwith a symlink to:\n  {}".format(
+            rllib_home, local_home),
+        abort=True)
+    if os.access(os.path.dirname(rllib_home), os.W_OK):
+        subprocess.check_call(["rm", "-rf", rllib_home])
+        subprocess.check_call(["ln", "-s", local_home, rllib_home])
+    else:
+        print("You don't have write permission to {}, using sudo:".format(
+            rllib_home))
+        subprocess.check_call(["sudo", "rm", "-rf", rllib_home])
+        subprocess.check_call(["sudo", "ln", "-s", local_home, rllib_home])
+    print("Created links.\n\nIf you run into issues initializing Ray, please "
+          "ensure that your local repo and the installed Ray is in sync "
+          "(pip install -U the latest wheels at "
+          "https://ray.readthedocs.io/en/latest/installation.html, "
+          "and ensure you are up-to-date on the master branch on git).\n\n"
+          "Note that you may need to delete the rllib symlink when pip "
+          "installing new Ray versions to prevent pip from overwriting files "
+          "in your git repo.")