[vpython] Fix flag parsing bug with "--".

[vpython] Fix flag parsing bug with "--".

When flags are being parsed, if a flag intended for Python (not vpython)
is encountered, and a subsequent argument includes "--", the parser will
only return flags between the Python flag and the "--" delimiter, not
the "--" delimiter or any arguments following it. This is incorrect.

Fix the parser to return all arguments past the Python flag instead, and
add a test for this.

BUG=None
TEST=unit

Review-Url: https://codereview.chromium.org/2937123003
Committed: https://github.com/luci/luci-go/commit/30e084f872754dca234b8e4104456f44ec5ee29c

[dnj, 2017-06-15 18:27:17]

dnj@chromium.org changed reviewers:
+ iannucci@chromium.org, qyearsley@chromium.org

[dnj, 2017-06-15 18:27:18]

PTAL!

[iannucci, 2017-06-15 19:04:55]

The CQ bit was checked by iannucci@chromium.org

[iannucci, 2017-06-15 19:04:56]

lgtm

[commit-bot: I haz the power, 2017-06-15 19:05:00]

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

[commit-bot: I haz the power, 2017-06-15 19:05:01]

This CL has an open dependency (Issue 2943513002 Patch 1). Please resolve the
dependency and try again.
If you are sure that there is no real dependency, please use one of the options
listed in https://goo.gl/9Es4OR to land the CL.

[dnj, 2017-06-15 19:30:59]

The CQ bit was checked by dnj@chromium.org

[commit-bot: I haz the power, 2017-06-15 19:31:12]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-06-15 19:37:21]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1497555059364650, "parent_rev":
"d9f6561f4b6d29a16f889ad4f6f2898c5794303a", "commit_rev":
"30e084f872754dca234b8e4104456f44ec5ee29c"}

[commit-bot: I haz the power, 2017-06-15 19:37:24]

Description was changed from

==========
[vpython] Fix flag parsing bug with "--".

When flags are being parsed, if a flag intended for Python (not vpython)
is encountered, and a subsequent argument includes "--", the parser will
only return flags between the Python flag and the "--" delimiter, not
the "--" delimiter or any arguments following it. This is incorrect.

Fix the parser to return all arguments past the Python flag instead, and
add a test for this.

BUG=None
TEST=unit
==========

to

==========
[vpython] Fix flag parsing bug with "--".

When flags are being parsed, if a flag intended for Python (not vpython)
is encountered, and a subsequent argument includes "--", the parser will
only return flags between the Python flag and the "--" delimiter, not
the "--" delimiter or any arguments following it. This is incorrect.

Fix the parser to return all arguments past the Python flag instead, and
add a test for this.

BUG=None
TEST=unit

Review-Url: https://codereview.chromium.org/2937123003
Committed:
https://github.com/luci/luci-go/commit/30e084f872754dca234b8e4104456f44ec5ee29c
==========

[commit-bot: I haz the power, 2017-06-15 19:37:25]

Committed patchset #1 (id:1) as
https://github.com/luci/luci-go/commit/30e084f872754dca234b8e4104456f44ec5ee29c

[qyearsley, 2017-06-15 20:12:54]

LGTM

https://codereview.chromium.org/2937123003/diff/1/vpython/application/flag.go
File vpython/application/flag.go (right):

https://codereview.chromium.org/2937123003/diff/1/vpython/application/flag.go...
vpython/application/flag.go:36: candidates := args
One thing that isn't very clear to me when reading this file is, what does
candidates refer to here? The candidates are a subset of the args, but what are
they candidates for? Candidates for being vpython args? Also, what is fsArgs?