clang: Instead of having update.sh clobber out/, add a define with the current revision.

clang: Instead of having update.sh clobber out/, add a define with the current revision.

When clang is turned on or off, or when clang is updated, all .o files and all
precompiled headers need to be rebuilt. This is currently done by having the
update script remove the out/ directory. This has issues:
* It fails to catch build directories with different names (e.g. out_android)
* It removes other build artifacts (like resources) that don't need rebuilding
* It doesn't happen when turning clang off (i.e. moving clang -> gcc).

Instead, let common.gypi add a define with the current clang revision to each
source file. This way, the clang revision is on each compile's command line
and the build system's commandline tracking can take care of the rebuilding.

BUG=nativeclient:3840
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=269427

[hans, 2014-05-08 20:11:20]

https://codereview.chromium.org/268363020/diff/1/build/common.gypi
File build/common.gypi (right):

https://codereview.chromium.org/268363020/diff/1/build/common.gypi#newcode2325
build/common.gypi:2325: 'defines':
['CR_CLANG_REVISION=<!(<(DEPTH)/tools/clang/scripts/update.sh
--print-revision)'],
Could we just shell out to clang and ask it which version it is?

[Nico, 2014-05-08 20:17:28]

Thanks!

https://codereview.chromium.org/268363020/diff/1/build/common.gypi
File build/common.gypi (right):

https://codereview.chromium.org/268363020/diff/1/build/common.gypi#newcode2325
build/common.gypi:2325: 'defines':
['CR_CLANG_REVISION=<!(<(DEPTH)/tools/clang/scripts/update.sh
--print-revision)'],
On 2014/05/08 20:11:21, hans wrote:
> Could we just shell out to clang and ask it which version it is?

Since --version prints 3 lines, it'd require some sed'ing, and I don't like sed
calls in gyp files, so I'd have to write a script for that. So this seems
simpler. (Also, once everything is on update.py, this could use pymod_do_main).

[hans, 2014-05-08 20:29:20]

On 2014/05/08 20:17:28, Nico wrote:
> Thanks!
> 
> https://codereview.chromium.org/268363020/diff/1/build/common.gypi
> File build/common.gypi (right):
> 
> https://codereview.chromium.org/268363020/diff/1/build/common.gypi#newcode2325
> build/common.gypi:2325: 'defines':
> ['CR_CLANG_REVISION=<!(<(DEPTH)/tools/clang/scripts/update.sh
> --print-revision)'],
> On 2014/05/08 20:11:21, hans wrote:
> > Could we just shell out to clang and ask it which version it is?
> 
> Since --version prints 3 lines, it'd require some sed'ing, and I don't like
sed
> calls in gyp files, so I'd have to write a script for that. So this seems
> simpler. (Also, once everything is on update.py, this could use
pymod_do_main).

I just figured it would reflect the dependency on the compiler version in a more
straight-forward way. For example, I will often be using a clang that didn't
come from the update script, and on Windows we don't have a pinned clang
version.

But I agree "clang --version" isn't appropriate.

Actually, if there was a convenient way to get the hash of clang, we could use
that. But this could be a future improvement :)

lgtm

[piman, 2014-05-08 20:44:37]

LGTM, thanks!!

[Nico, 2014-05-08 21:01:51]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2014-05-08 21:07:43]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/thakis@chromium.org/268363020/20001

[commit-bot: I haz the power, 2014-05-09 22:01:32]

Change committed as 269427