test: make round-trip-syntax-test Python 3 friendly

Make the `round-trip-syntax-test` tool Python 3 friendly by tweaking the
open modes and using `reduce` from `functools` as it has been removed in
Python 3.

Author: compnerd

utils/round-trip-syntax-test

@@ -4,6 +4,7 @@ from __future__ import print_function, unicode_literals
 
 import argparse
 import difflib
+from functools import reduce
 import logging
 import os
 import subprocess
@@ -17,7 +18,8 @@ class RoundTripTask(object):
     def __init__(self, input_filename, action, swift_syntax_test,
                  skip_bad_syntax):
         assert action == '-round-trip-parse' or action == '-round-trip-lex'
-        assert type(input_filename) == unicode
+        if sys.version_info[0] < 3:
+            assert type(input_filename) == unicode
         assert type(swift_syntax_test) == str
 
         assert os.path.isfile(input_filename), \
@@ -51,9 +53,9 @@ class RoundTripTask(object):
         self.output_file.close()
         self.stderr_file.close()
 
-        with open(self.output_file.name, 'r') as stdout_in:
+        with open(self.output_file.name, 'rb') as stdout_in:
             self.stdout = stdout_in.read()
-        with open(self.stderr_file.name, 'r') as stderr_in:
+        with open(self.stderr_file.name, 'rb') as stderr_in:
             self.stderr = stderr_in.read()
 
         os.remove(self.output_file.name)
@@ -75,7 +77,7 @@ class RoundTripTask(object):
                 raise RuntimeError()
 
         contents = ''.join(map(lambda l: l.decode('utf-8', errors='replace'),
-                               open(self.input_filename).readlines()))
+                               open(self.input_filename, 'rb').readlines()))
         stdout_contents = self.stdout.decode('utf-8', errors='replace')
 
         if contents == stdout_contents:
@@ -92,7 +94,7 @@ def swift_files_in_dir(d):
     swift_files = []
     for root, dirs, files in os.walk(d):
         for basename in files:
-            if not basename.decode('utf-8').endswith('.swift'):
+            if not basename.endswith('.swift'):
                 continue
             abs_file = os.path.abspath(os.path.join(root, basename))
             swift_files.append(abs_file)
@@ -149,7 +151,8 @@ This driver invokes swift-syntax-test using -round-trip-lex and
     all_input_files = [filename for dir_listing in dir_listings
                        for filename in dir_listing]
     all_input_files += args.individual_input_files
-    all_input_files = [f.decode('utf-8') for f in all_input_files]
+    if sys.version_info[0] < 3:
+        all_input_files = [f.decode('utf-8') for f in all_input_files]
 
     if len(all_input_files) == 0:
         logging.error('No input files!')