Update infrastructure python code to be compatible with python 2 and python 3 (flutter/engine#39133)

* Compatibility with python2 and python3

* Formatting

* Updated to use a function instead of decoding bytes in multiple places.

* Formatting and whitespace cleanup.

* Fix import statement.

* Linter change for docstring.

* Formatting.

* Remove function from run_tests.py since it is a pain to import.

* Add todo message for python 2 deprecation.

* Updated copyright year.

engine/src/flutter/ci/compatibility_helper.py

@@ -0,0 +1,25 @@
+#!/usr/bin/env python3
+#
+# Copyright 2013 The Flutter Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+#
+# This script contains helper function(s) for supporting both
+# python 2 and python 3 infrastructure code.
+
+ENCODING = 'UTF-8'
+
+
+def byte_str_decode(str_or_bytes):
+  """Returns a string if given either a string or bytes.
+
+    TODO: This function should be removed when the supported python
+    version is only python 3.
+
+    Args:
+        str_or_bytes (string or bytes) we want to convert or return as
+        the possible value changes depending on the version of python
+        used.
+    """
+  return str_or_bytes if isinstance(str_or_bytes,
+                                    str) else str_or_bytes.decode(ENCODING)

engine/src/flutter/ci/firebase_testlab.py

@@ -10,6 +10,7 @@ import re
 import os
 import subprocess
 import sys
+from compatibility_helper import byte_str_decode
 
 if 'STORAGE_BUCKET' not in os.environ:
   print('The GCP storage bucket must be provided as an environment variable.')
@@ -67,6 +68,7 @@ def check_logcat(results_dir):
       'gsutil', 'cat',
       '%s/%s/*/logcat' % (BUCKET, results_dir)
   ])
+  logcat = byte_str_decode(logcat)
   if not logcat:
     sys.exit(1)
 
@@ -82,7 +84,9 @@ def check_timeline(results_dir):
       'gsutil', 'du',
       '%s/%s/*/game_loop_results/results_scenario_0.json' %
       (BUCKET, results_dir)
-  ]).strip()
+  ])
+  gsutil_du = byte_str_decode(gsutil_du)
+  gsutil_du = gsutil_du.strip()
   if gsutil_du == '0':
     print('Failed to produce a timeline.')
     sys.exit(1)
@@ -113,8 +117,9 @@ def main():
     return 1
 
   git_revision = subprocess.check_output(['git', 'rev-parse', 'HEAD'],
-                                         cwd=script_dir).strip()
-
+                                         cwd=script_dir)
+  git_revision = byte_str_decode(git_revision)
+  git_revision = git_revision.strip()
   results = []
   apk = None
   for apk in apks:

engine/src/flutter/ci/scan_flattened_deps.py

@@ -17,6 +17,7 @@ import shutil
 import subprocess
 import sys
 from urllib import request
+from compatibility_helper import byte_str_decode
 
 SCRIPT_DIR = os.path.dirname(sys.argv[0])
 CHECKOUT_ROOT = os.path.realpath(os.path.join(SCRIPT_DIR, '..'))
@@ -206,7 +207,9 @@ def get_common_ancestor_commit(dep, deps_list):
         'git --git-dir ' + temp_dep_dir + '/.git remote show upstream ' +
         "| sed -n \'/HEAD branch/s/.*: //p\'",
         shell=True
-    ).decode().strip()
+    )
+    default_branch = byte_str_decode(default_branch)
+    default_branch = default_branch.strip()
     print(
         'default_branch found: {default_branch}'.format(
             default_branch=default_branch
@@ -223,7 +226,8 @@ def get_common_ancestor_commit(dep, deps_list):
         "--format=\'%(objectname:short)\' refs/heads/upstream",
         shell=True
     )
-    commit = commit.decode().strip()
+    commit = byte_str_decode(commit)
+    commit = commit.strip()
 
     # perform merge-base on most recent default branch commit and pinned mirror commit
     ancestor_commit = subprocess.check_output(
@@ -232,7 +236,8 @@ def get_common_ancestor_commit(dep, deps_list):
         ),
         shell=True
     )
-    ancestor_commit = ancestor_commit.decode().strip()
+    ancestor_commit = byte_str_decode(ancestor_commit)
+    ancestor_commit = ancestor_commit.strip()
     print('Ancestor commit: ' + ancestor_commit)
     return ancestor_commit
   except subprocess.CalledProcessError as error:

engine/src/flutter/testing/run_tests.py

@@ -33,6 +33,7 @@ ROBOTO_FONT_PATH = os.path.join(FONTS_DIR, 'Roboto-Regular.ttf')
 FONT_SUBSET_DIR = os.path.join(BUILDROOT_DIR, 'flutter', 'tools', 'font-subset')
 
 FML_UNITTESTS_FILTER = '--gtest_filter=-*TimeSensitiveTest*'
+ENCODING = 'UTF-8'
 
 
 def print_divider(char='='):
@@ -598,6 +599,11 @@ def ensure_ios_tests_are_built(ios_out_dir):
 def assert_expected_xcode_version():
   """Checks that the user has a version of Xcode installed"""
   version_output = subprocess.check_output(['xcodebuild', '-version'])
+  # TODO ricardoamador: remove this check when python 2 is deprecated.
+  version_output = version_output if isinstance(
+      version_output, str
+  ) else version_output.decode(ENCODING)
+  version_output = version_output.strip()
   match = re.match(r'Xcode (\d+)', version_output)
   message = 'Xcode must be installed to run the iOS embedding unit tests'
   assert match, message