clang update script: Verify that VERSION is correct.

tools/clang/scripts/update.py

Index: tools/clang/scripts/update.py
diff --git a/tools/clang/scripts/update.py b/tools/clang/scripts/update.py
index 5cdfbae506b8ffb0b69a313f85991c81478adfc7..d24349c944fdfe27ec72364dc971535ac6b99414 100755
--- a/tools/clang/scripts/update.py
+++ b/tools/clang/scripts/update.py
@@ -373,6 +373,24 @@ def CopyDiaDllTo(target_dir):
   CopyFile(dia_dll, target_dir)
 
 
+def VeryifyVersionOfBuiltClangMatchesVERSION():
+  """Checks that `clang --version` outputs VERSION.  If this fails, VERSION
+  in this file is out-of-date and needs to be updated (possibly in an
+  `if use_head_revision:` block in main() first)."""
+  clang = os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')
+  if sys.platform == 'win32':
+    # TODO: Parse `clang-cl /?` output for built clang's version and check that
+    # to check the binary we're actually shipping? But clang-cl.exe is just
+    # a copy of clang.exe, so this does check the same thing.
+    clang += '.exe'

[hans, 2016/08/08 18:54:00]

Yeah, I think checking clang is good enough.

If we *really* wanted to, we could do "clang-cl.exe --driver-mode=gcc", which we
could pass --version too and it will behave just like clang.exe. But that also
seems like a lot of hoops to jump through.

+  version_out = subprocess.check_output([clang, '--version'])
+  version_out = re.match(r'clang version (\S+)', version_out).group(1)

[hans, 2016/08/08 18:54:00]

Sorry, I should have mentioned this the first time: Perhaps \S might be too
broad? Could we check for [0-9.]+ instead?

[Nico, 2016/08/08 19:00:31]

Does it matter if we compare to VERSION later? If it always matches too much
we'll find out then. But I can make it [0-9.] too if you think it' s important.

[hans, 2016/08/08 19:27:32]

I figured if for whatever reason clang starts printing "4.0.0-trunk" instead of
just "4.0.0" or whatever, that would unnecessarily break this test. Sure we'd
catch it, but it would be annoying.

[Nico, 2016/08/08 20:26:20]

Hm, I think I'd prefer if this turned red in that case (maybe the headers are
now in include/clang/4.0.0-trunk too) so we'd catch if this changes in
surprising ways.

But I also think it's less important than the time we're going to spend arguing
about this, so done :-)

+  if version_out != VERSION:
+    print ('unexpected clang version %s (not %s), update VERSION in update.py'
+           % (version_out, VERSION))
+    sys.exit(1)
+
+
 def UpdateClang(args):
   print 'Updating Clang to %s...' % PACKAGE_VERSION
 
@@ -648,7 +666,7 @@ def UpdateClang(args):
   elif sys.platform.startswith('linux'):
     RunCommand(['strip', os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')])
 
-  # TODO(thakis): Check that `clang --version` matches VERSION.
+  VeryifyVersionOfBuiltClangMatchesVERSION()
 
   # Do an out-of-tree build of compiler-rt.
   # On Windows, this is used to get the 32-bit ASan run-time.