Windows: Fix custom toolchain args with GN

Windows: Fix custom toolchain args with GN

BUG=623342

[Marshall, 2016-07-07 21:28:32]

Description was changed from

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Windows: Fix custom toolchain args with GN

BUG=623342
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to

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Windows: Fix custom toolchain args with GN

BUG=623342
==========

[Marshall, 2016-07-07 21:28:32]

marshall@chromium.org changed reviewers:
+ brucedawson@chromium.org, dpranke@chromium.org

[Marshall, 2016-07-07 21:29:36]

Please review. Including both brucedawson@ and dpranke@ because I'm not sure
who's working on Windows GN support. Please feel free to remove and/or modify
reviewers as appropriate.

[brucedawson, 2016-07-07 23:31:39]

Adding Scott in case he has feedback, but probably not.

https://codereview.chromium.org/2128993002/diff/1/build/config/win/visual_stu...
File build/config/win/visual_studio_version.gni (right):

https://codereview.chromium.org/2128993002/diff/1/build/config/win/visual_stu...
build/config/win/visual_studio_version.gni:34: assert(visual_studio_runtime_dirs
!= "",
It would be best to give an example of what to set them to. i.e.;

visual_studio_version = "2015"
visual_studio_runtime_dirs = ...

Otherwise it's difficult to figure out what is actually needed (2015? VS2015?)

https://codereview.chromium.org/2128993002/diff/1/build/toolchain/win/setup_t...
File build/toolchain/win/setup_toolchain.py (right):

https://codereview.chromium.org/2128993002/diff/1/build/toolchain/win/setup_t...
build/toolchain/win/setup_toolchain.py:131: variables = []
My only concern is that this might make some failures more cryptic than before.
That is, what happens if the necessary environment variables aren't set? This
should be detected as early as possible so that a helpful error message can be
shown.

Perhaps require that INCLUDE, LIB, etc. be set and if they aren't then raise an
exception saying what the problem is.

We've had cases in the past where errors propagated too far and it took years to
trace them back.

[Dirk Pranke, 2016-08-09 03:42:56]

@marshall - are you still interested in this CL, or should we close it?

[Marshall, 2016-08-12 14:47:54]

On 2016/08/09 03:42:56, Dirk Pranke (slow) wrote:
> @marshall - are you still interested in this CL, or should we close it?

Closing this for now. The use of setup_toolchain.py, vs_toolchain.py,
environment.* files, DEPOT_TOOLS_WIN_TOOLCHAIN, GYP_MSVS_OVERRIDE_PATH, various
GN variables, and VS detection in general feels overly complicated. Maybe it
would be better to agree on a single source of truth (JSON file or GN
variables), and then just reference that from everywhere.