[LIT] Make util.executeCommand python3 friendly

[EricWF]

Summary

The parameter input to subprocess.Popen.communicate(...) must be an object of type bytes . This is strictly enforced in python3. This patch (1) allows to_bytes to be safely called redundantly. (2) Explicitly convert input within executeCommand. This allows for usages like executeCommand(['clang++', '-'], input='int main() {}\n').

[dim]

LGTM, though I am not a python 3 expert, by any means. :)

[EricWF]

Accepting. There hasn't been a lot of interest and this seems fine for post-commit review.

utils/lit/lit/util.py

 import errno
 import itertools
 import math
 import os
 import platform
 import signal
 import subprocess
 import sys
 import threading
 
 def to_bytes(str):
     # Encode to UTF-8 to get binary data.
+    if isinstance(str, bytes):
+        return str
     return str.encode('utf-8')
 
 def to_string(bytes):
     if isinstance(bytes, str):
         return bytes
     return to_bytes(bytes)
 
 def convert_string(bytes):
"""
         Returns a tuple (out, err, exitCode) where
         * ``out`` (str) is the standard output of running the command
         * ``err`` (str) is the standard error of running the command
         * ``exitCode`` (int) is the exitCode of running the command
 
         If the timeout is hit an ``ExecuteCommandTimeoutException``
         is raised.
     """
+    if input is not None:
+        input = to_bytes(input)
     p = subprocess.Popen(command, cwd=cwd,
                          stdin=subprocess.PIPE,
                          stdout=subprocess.PIPE,
                          stderr=subprocess.PIPE,
                          env=env, close_fds=kUseCloseFDs)
     timerObject = None
     # FIXME: Because of the way nested function scopes work in Python 2.x we
     # need to use a reference to a mutable object rather than a plain