[lit] Fix problem in how Python versions open files with different encodings

Summary:
This issue was found when running the clang unit test on Windows. Python 3.x cannot open some of the files that the tests are using with a simple open because of their encoding. Python 2.7+ and Python 3.x both support io.open which allows for an encoding to be specified. 

This change will determine whether two files being compared should be opened (and then compared) as text or binary and whether to use utf-8 or the default encoding before proceeding with a line-by-line comparison.

Patch by Stella Stamenova!

Reviewers: zturner, llvm-commits, rnk, MaggieYi

Reviewed By: zturner

Subscribers: asmith, MatzeB, stella.stamenova, delcypher, llvm-commits

Differential Revision: https://reviews.llvm.org/D43165

llvm-svn: 329012

llvm/utils/lit/lit/TestRunner.py

@@ -2,6 +2,7 @@ from __future__ import absolute_import
 import difflib
 import errno
 import functools
+import io
 import itertools
 import getopt
 import os, signal, subprocess, sys
@@ -386,9 +387,51 @@ def executeBuiltinDiff(cmd, cmd_shenv):
             return path, sorted(child_trees)
 
     def compareTwoFiles(filepaths):
+        compare_bytes = False
+        encoding = None
         filelines = []
         for file in filepaths:
-            with open(file, 'r') as f:
+            try:
+                with open(file, 'r') as f:
+                    filelines.append(f.readlines())
+            except UnicodeDecodeError:
+                try:
+                    with open(file, 'r', encoding="utf-8") as f:
+                        filelines.append(f.readlines())
+                    encoding = "utf-8"
+                except:
+                    compare_bytes = True
+
+        if compare_bytes:
+            return compareTwoBinaryFiles(filepaths)
+        else:
+            return compareTwoTextFiles(filepaths, encoding)
+
+    def compareTwoBinaryFiles(filepaths):
+        filelines = []
+        for file in filepaths:
+            with open(file, 'rb') as f:
+                filelines.append(f.readlines())
+
+        exitCode = 0 
+        if hasattr(difflib, 'diff_bytes'):
+            # python 3.5 or newer
+            diffs = difflib.diff_bytes(difflib.unified_diff, filelines[0], filelines[1], filepaths[0].encode(), filepaths[1].encode())
+            diffs = [diff.decode() for diff in diffs]
+        else:
+            # python 2.7
+            func = difflib.unified_diff if unified_diff else difflib.context_diff
+            diffs = func(filelines[0], filelines[1], filepaths[0], filepaths[1])
+
+        for diff in diffs:
+            stdout.write(diff)
+            exitCode = 1
+        return exitCode
+
+    def compareTwoTextFiles(filepaths, encoding):
+        filelines = []
+        for file in filepaths:
+            with open(file, 'r', encoding=encoding) as f:
                 filelines.append(f.readlines())
 
         exitCode = 0