Uncouple the cros_custom_toolchain from chromeos.

Uncouple the cros_custom_toolchain from chromeos.

It could equally easily be used to bring your own toolchain.
This frees up open source advocates to try out even more pieces,
even more easily.  This also keeps us from abusing the
distinction of cross compilers in ultimately unwise ways.

BUG=None
TEST=None, on purpose - easy does not mean supported.

[Peter Mayo, 2015-08-13 02:35:16]

petermayo@chromium.org changed reviewers:
+ dpranke@chromium.org

[Dirk Pranke, 2015-08-13 20:25:16]

https://codereview.chromium.org/1287153002/diff/1/build/config/BUILDCONFIG.gn
File build/config/BUILDCONFIG.gn (right):

https://codereview.chromium.org/1287153002/diff/1/build/config/BUILDCONFIG.gn...
build/config/BUILDCONFIG.gn:151: cros_use_custom_toolchain = false
if this is no longer strictly tied to CrOS, should this just be called
'use_custom_toolchain', etc.?

[Peter Mayo, 2015-08-13 21:22:47]

On 2015/08/13 20:25:16, Dirk Pranke wrote:
> https://codereview.chromium.org/1287153002/diff/1/build/config/BUILDCONFIG.gn
> File build/config/BUILDCONFIG.gn (right):
> 
>
https://codereview.chromium.org/1287153002/diff/1/build/config/BUILDCONFIG.gn...
> build/config/BUILDCONFIG.gn:151: cros_use_custom_toolchain = false
> if this is no longer strictly tied to CrOS, should this just be called
> 'use_custom_toolchain', etc.?

I thought about that, but the indirection through the toolchain needs to be
called something.  Renaming cros/BUILD to custom/BUILD and breaking any existing
args.gn seemed more traumatic.

Since in the end it makes more sense, do you think it is worth the short term
pain?

[Dirk Pranke, 2015-08-13 21:43:01]

On 2015/08/13 21:22:47, Peter Mayo wrote:
> On 2015/08/13 20:25:16, Dirk Pranke wrote:
> >
https://codereview.chromium.org/1287153002/diff/1/build/config/BUILDCONFIG.gn
> > File build/config/BUILDCONFIG.gn (right):
> > 
> >
>
https://codereview.chromium.org/1287153002/diff/1/build/config/BUILDCONFIG.gn...
> > build/config/BUILDCONFIG.gn:151: cros_use_custom_toolchain = false
> > if this is no longer strictly tied to CrOS, should this just be called
> > 'use_custom_toolchain', etc.?
> 
> I thought about that, but the indirection through the toolchain needs to be
> called something.  Renaming cros/BUILD to custom/BUILD and breaking any
existing
> args.gn seemed more traumatic.
> 
> Since in the end it makes more sense, do you think it is worth the short term
> pain?

I think we can leave it as cros_use for now; if it turns out that others end up
using this, we can
look into renaming things.

[Peter Mayo, 2015-08-20 20:08:43]

On 2015/08/13 21:43:01, Dirk Pranke wrote:
> On 2015/08/13 21:22:47, Peter Mayo wrote:
> > On 2015/08/13 20:25:16, Dirk Pranke wrote:
> > >
> https://codereview.chromium.org/1287153002/diff/1/build/config/BUILDCONFIG.gn
> > > File build/config/BUILDCONFIG.gn (right):
> > > 
> > >
> >
>
https://codereview.chromium.org/1287153002/diff/1/build/config/BUILDCONFIG.gn...
> > > build/config/BUILDCONFIG.gn:151: cros_use_custom_toolchain = false
> > > if this is no longer strictly tied to CrOS, should this just be called
> > > 'use_custom_toolchain', etc.?
> > 
> > I thought about that, but the indirection through the toolchain needs to be
> > called something.  Renaming cros/BUILD to custom/BUILD and breaking any
> existing
> > args.gn seemed more traumatic.
> > 
> > Since in the end it makes more sense, do you think it is worth the short
term
> > pain?
> 
> I think we can leave it as cros_use for now; if it turns out that others end
up
> using this, we can
> look into renaming things.

Ping?

[Dirk Pranke, 2015-08-20 21:10:03]

lgtm

[Peter Mayo, 2015-08-24 15:49:26]

The CQ bit was checked by petermayo@chromium.org

[commit-bot: I haz the power, 2015-08-24 15:50:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1287153002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1287153002/1

[commit-bot: I haz the power, 2015-08-24 15:59:25]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-24 15:59:26]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

[Peter Mayo, 2015-08-24 16:10:06]

petermayo@chromium.org changed reviewers:
+ brettw@chromium.org

[Peter Mayo, 2015-08-24 16:10:07]

** Presubmit ERRORS **
Missing LGTM from an OWNER for these files:
    build/config/BUILDCONFIG.gn

[brettw, 2015-08-24 20:30:52]

I don't understand the motivation for this change. Is this something
specifically that came up? I don't understand the part about freeing up open
source advocates or what cross compilation abuse this is preventing.

[Peter Mayo, 2015-08-24 20:45:22]

On 2015/08/24 20:30:52, brettw wrote:
> I don't understand the motivation for this change. Is this something
> specifically that came up?

No, hence no bug.

> I don't understand the part about freeing up open
> source advocates or what cross compilation abuse this is preventing.

There was a discussion about open source advocates being able to bring their own
toolchain to chromium compiles, as part of making clearer the opennness of
chromium.  Routinely proving we can do that by having a platform that does seems
like a step in the right direction, and adding a relatively arbitrary condition
that the target OS = "chromeos" hinders taking the next steps.

At the same time the easiest, most straightfoward test that we are targeting a
chromeos device is to see whether we are using this mechanism.  That ties two
unrelated but coincidental concepts together.

[brettw, 2015-08-24 20:54:24]

A compiler suite as defined by random open source people is different than a GN
toolchain. This change doesn't clearly make anything easier from what I can
tell, and if we want this I would want to understand exactly what they're trying
to do before speculatively adding features that nobody uses today.

If we do this, it shouldn't be called "cros" and it should be in an is_linux
block since it's only used on Linux.