[Py3] Make build.py python3 compatible

Couple of fixes here include:
- change `file` to `open`
- add `universal_newlines=True` to subprocess calls, since the output is
later compared to a string
- change buffer to line buffer, this is the only "breaking" change that
might cause a different behavior.

For the buffer behavior, unbuffered output is only allowed in binary
mode, but we are always printing strings. So the compromise here is to
use line buffering (we could also omit it).

Bug: v8:9871,chromium:941669
Change-Id: I5c1e69da022d13f4234921fe5fe717d53c96f058
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2252867
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Cr-Commit-Position: refs/heads/master@{#781911}

tools/clang/scripts/build.py

@@ -14,6 +14,7 @@ from __future__ import print_function
 
 import argparse
 import glob
+import io
 import json
 import os
 import pipes
@@ -215,7 +216,7 @@ def CreateChromeToolsShim():
   tool detection logic munges them in a weird way."""
   assert not any(i in os.path.basename(CHROME_TOOLS_SHIM_DIR) for i in '-_')
   os.mkdir(CHROME_TOOLS_SHIM_DIR)
-  with file(os.path.join(CHROME_TOOLS_SHIM_DIR, 'CMakeLists.txt'), 'w') as f:
+  with open(os.path.join(CHROME_TOOLS_SHIM_DIR, 'CMakeLists.txt'), 'w') as f:
     f.write('# Automatically generated by tools/clang/scripts/update.py. ' +
             'Do not edit.\n')
     f.write('# Since tools/clang is located in another directory, use the \n')
@@ -326,7 +327,8 @@ def VerifyVersionOfBuiltClangMatchesVERSION():
   clang = os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')
   if sys.platform == 'win32':
     clang += '-cl.exe'
-  version_out = subprocess.check_output([clang, '--version'])
+  version_out = subprocess.check_output([clang, '--version'],
+                                        universal_newlines=True)
   version_out = re.match(r'clang version ([0-9.]+)', version_out).group(1)
   if version_out != RELEASE_VERSION:
     print(('unexpected clang version %s (not %s), '
@@ -339,9 +341,11 @@ def CopyLibstdcpp(args, build_dir):
   if not args.gcc_toolchain:
     return
   # Find libstdc++.so.6
-  libstdcpp = subprocess.check_output(
-      [os.path.join(args.gcc_toolchain, 'bin', 'g++'),
-       '-print-file-name=libstdc++.so.6']).rstrip()
+  libstdcpp = subprocess.check_output([
+      os.path.join(args.gcc_toolchain, 'bin', 'g++'),
+      '-print-file-name=libstdc++.so.6'
+  ],
+                                      universal_newlines=True).rstrip()
 
   # Copy libstdc++.so.6 into the build dir so that the built binaries can find
   # it. Binaries get their rpath set to $origin/../lib/. For clang, lld,
@@ -431,7 +435,16 @@ def main():
 
 
   # Don't buffer stdout, so that print statements are immediately flushed.
-  sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)
+  # LLVM tests print output without newlines, so with buffering they won't be
+  # immediately printed.
+  major, _, _, _, _ = sys.version_info
+  if major == 3:
+    # Python3 only allows unbuffered output for binary streams. This
+    # workaround comes from https://stackoverflow.com/a/181654/4052492.
+    sys.stdout = io.TextIOWrapper(open(sys.stdout.fileno(), 'wb', 0),
+                                  write_through=True)
+  else:
+    sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)
 
   # The gnuwin package also includes curl, which is needed to interact with the
   # github API below.