gclient: Fix gclient Python 3 errors and add to presubmit tests.

Bug: 984182
Change-Id: I06e88f56aebf31c0c1ca495e6cbf03b6698b3676
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1790603Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

gclient.py

@@ -241,13 +241,14 @@ class Hook(object):
 
     cmd = [arg for arg in self._action]
 
-    if cmd[0] == 'python' and six.PY2:
+    if cmd[0] == 'python':
       # If the hook specified "python" as the first item, the action is a
       # Python script. Run it by starting a new copy of the same interpreter if
       # we're running on Python 2.
-      # On Python 3 we simply execute 'python'.
-      cmd[0] = sys.executable
-    elif cmd[0] == 'vpython' and _detect_host_os() == 'win':
+      # When using vpython3, "python" refers to the Python 3 executable used by
+      # vpython3, so use "vpython" instead.
+      cmd[0] = sys.executable if six.PY2 else 'vpython'
+    if cmd[0] == 'vpython' and _detect_host_os() == 'win':
       cmd[0] += '.bat'
 
     try:
@@ -2707,7 +2708,7 @@ def CMDsync(parser, args):
           'url': str(d.url) if d.url else None,
           'was_processed': d.should_process,
       }
-    with open(options.output_json, 'wb') as f:
+    with open(options.output_json, 'w') as f:
       json.dump({'solutions': slns}, f)
   return ret
 
@@ -2862,7 +2863,7 @@ def CMDgetdep(parser, args):
   if client is not None:
     builtin_vars = client.get_builtin_vars()
   else:
-    logging.warn(
+    logging.warning(
         'Couldn\'t find a valid gclient config. Will attempt to parse the DEPS '
         'file without support for built-in variables.')
     builtin_vars = None
@@ -2922,7 +2923,7 @@ def CMDsetdep(parser, args):
   if client is not None:
     builtin_vars = client.get_builtin_vars()
   else:
-    logging.warn(
+    logging.warning(
         'Couldn\'t find a valid gclient config. Will attempt to parse the DEPS '
         'file without support for built-in variables.')
     builtin_vars = None

testing_support/fake_cipd.py

@@ -37,7 +37,7 @@ def main():
     new_content = parse_cipd(args.root, f.readlines())
 
   # Install new packages
-  for path, packages in new_content.iteritems():
+  for path, packages in new_content.items():
     if not os.path.exists(path):
       os.makedirs(path)
     with open(os.path.join(path, '_cipd'), 'w') as f:

tests/gclient_smoketest.py

-#!/usr/bin/env python
+#!/usr/bin/env vpython3
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
@@ -734,13 +734,7 @@ class GClientSmokeGIT(GClientSmokeBase):
         ('running', self.root_dir),                 # pre-deps hook
         ('running', self.root_dir),                 # pre-deps hook (fails)
     ]
-    executable = sys.executable
-    # On Python 3 we always execute hooks with 'python', so we cannot use
-    # sys.executable.
-    if sys.version_info.major == 3:
-      executable = subprocess.check_output(
-          ['python', '-c', 'import sys; print(sys.executable)'])
-      executable = executable.decode('utf-8').strip()
+    executable = sys.executable if sys.version_info.major == 2 else 'vpython'
     expected_stderr = ("Error: Command '%s -c import sys; "
                        "sys.exit(1)' returned non-zero exit status 1 in %s\n"
                        % (executable, self.root_dir))