Allow sysroot to be overridden via GN arguments when using target toolchain.

Allow sysroot to be overridden via GN arguments when using target toolchain.

The GYP flow allows 'sysroot' to be overridden via GYP_DEFINES, which is needed
in some scenarios such as building for Chrome OS. This CL declares
'target_sysroot' as a GN argument, which can be used to override the default
sysroot when compiling using the target toolchain via the GN flow.

BUG=427726
TEST=Verify that sysroot is overridden via `gn gen --args='target_sysroot=...' ...`

Committed: https://crrev.com/4a8f241213d5618a152bc00cc4eaeb556b63d765
Cr-Commit-Position: refs/heads/master@{#301868}

[Ben Chan, 2014-10-28 23:11:47]

benchan@chromium.org changed reviewers:
+ brettw@chromium.org, cmasone@chromium.org, jamesr@chromium.org,
vapier@chromium.org

[Ben Chan, 2014-10-28 23:11:48]

If there is a better approach, please let me know. I'm not sure if it's a good
idea to allow sysroot to be overridden.

[vapier, 2014-10-28 23:15:34]

imo, sysroot should be fully controllable by the end user.  these random paths
we have hardcoded might work in our internal build envs, but they make no sense
for end peeps trying to build things.

i would lgtm, this but i've never looked at a .gn file before, so i'll just lgtm
the concept :).

[brettw, 2014-10-29 01:37:43]

I'm not sure this patch is quite right in the presence of cross-compiles. The
sysroot variable currently defines the current toolchain's sysroot. If you set
the variable, it will get defined for all toolchains, which is almost surely not
what you want.

How about at the top define a "target_sysroot" variable and set it to empty,
documenting that this is the sysroot applied to the target toolchain, empty
means use the default.

Then do:

if (current_toolchain == default_toolchain) {
  sysroot = target_sysroot
} else ... everything else in that file ...

[Ben Chan, 2014-10-29 07:14:35]

Patchset #2 (id:20001) has been deleted

[Ben Chan, 2014-10-29 07:16:27]

On 2014/10/29 01:37:43, brettw wrote:
> I'm not sure this patch is quite right in the presence of cross-compiles. The
> sysroot variable currently defines the current toolchain's sysroot. If you set
> the variable, it will get defined for all toolchains, which is almost surely
not
> what you want.
> 
> How about at the top define a "target_sysroot" variable and set it to empty,
> documenting that this is the sysroot applied to the target toolchain, empty
> means use the default.
> 
> Then do:
> 
> if (current_toolchain == default_toolchain) {
>   sysroot = target_sysroot
> } else ... everything else in that file ...

sgtm, I will drop the other CL. PTAL

[brettw, 2014-10-29 16:44:38]

lgtm

[Ben Chan, 2014-10-29 16:50:02]

The CQ bit was checked by benchan@chromium.org

[commit-bot: I haz the power, 2014-10-29 16:50:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/683063005/40001

[commit-bot: I haz the power, 2014-10-29 17:37:03]

Committed patchset #2 (id:40001)

[commit-bot: I haz the power, 2014-10-29 17:37:36]

Patchset 2 (id:??) landed as
https://crrev.com/4a8f241213d5618a152bc00cc4eaeb556b63d765
Cr-Commit-Position: refs/heads/master@{#301868}