Make use_system_mesa switch work: make symlinks

Make use_system_mesa switch work: make symlinks
for nacl untrusted build.

BUG=161389
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=178028

[Mark Mentovai, 2013-01-18 17:38:45]

https://codereview.chromium.org/11862016/diff/1/third_party/khronos/khronos.gyp
File third_party/khronos/khronos.gyp (right):

https://codereview.chromium.org/11862016/diff/1/third_party/khronos/khronos.g...
third_party/khronos/khronos.gyp:57:
'<(khronos_headers_symlink_target)/.dummy_gles2',
What’s your theory here? You just want to run this ln -s on each and every
build?

https://codereview.chromium.org/11862016/diff/1/third_party/khronos/khronos.g...
third_party/khronos/khronos.gyp:60: 'ln', '-s',
What happens when you run this command more than once (like on a rebuild)?
Something like “ln: File exists”?

[Paweł Hajdan Jr., 2013-01-18 18:36:43]

https://codereview.chromium.org/11862016/diff/1/third_party/khronos/khronos.gyp
File third_party/khronos/khronos.gyp (right):

https://codereview.chromium.org/11862016/diff/1/third_party/khronos/khronos.g...
third_party/khronos/khronos.gyp:57:
'<(khronos_headers_symlink_target)/.dummy_gles2',
On 2013/01/18 17:38:45, Mark Mentovai wrote:
> What’s your theory here? You just want to run this ln -s on each and every
> build?

I can't have empty 'outputs', and the real output is a directory. I'm not sure
what to do with this.

https://codereview.chromium.org/11862016/diff/1/third_party/khronos/khronos.g...
third_party/khronos/khronos.gyp:60: 'ln', '-s',
On 2013/01/18 17:38:45, Mark Mentovai wrote:
> What happens when you run this command more than once (like on a rebuild)?
> Something like “ln: File exists”?

That could be "solved" with 'ln -sf', but if there is a solution that doesn't
run this on every build unconditionally, that would be great. Is there one, is
there a better way?

[Mark Mentovai, 2013-01-18 18:54:35]

The best I can come up with is to have the .gyp file itself be the input, and
have the output be some file next to the directory that gets touched at the same
time that you make the symlink.

You’d still need to use ln -sf.

[Paweł Hajdan Jr., 2013-01-18 20:46:01]

On 2013/01/18 18:54:35, Mark Mentovai wrote:
> The best I can come up with is to have the .gyp file itself be the input,

Done.

> and have the output be some file next to the directory that gets touched at
the same
> time that you make the symlink.

Looks like I'd need to add a special .py script to touch a file and make a
symlink in a single action, right? I'm not sure if it's worth it, since when
distros build from source it's usually with a clean output directory, and a
one-time build.

If you think this should be done, I can do that, and it seems pretty easy.

> You’d still need to use ln -sf.

Done.

[Mark Mentovai, 2013-01-18 20:48:48]

I think it’s worth it to avoid resymlinking each time. That’s bad for builds and
it sets a bad precedent. You can put the symlink+touch script somewhere in build
or something and then recycle it if this problem comes up elsewhere.

[Paweł Hajdan Jr., 2013-01-18 23:51:30]

Done. PTAL.

[Mark Mentovai, 2013-01-19 16:03:33]

LGTM