Allow --3way to be passed to `git apply` via `git cl patch`.

Default to using --3way when using `git cl patch` with git >= 1.7.12

Git introduced a --3way argument to `apply` in version 1.7.12 [1]. This
provides a much nicer way to apply issues from Rietveld.

After this change, `git cl patch` will add --3way after checking the git
version for support.

[1] https://github.com/git/git/commit/f247b10aa0f75727f1b4bdd67b060720b8219b29

BUG=None
TEST=Ran `git cl patch <issue>` with both clean and unclean patches,
also checked behaviour of --reject is preserved.
R=maruel@chromium.org

[M-A Ruel, 2013-06-05 18:47:33]

https://codereview.chromium.org/16211005/diff/4001/git_cl.py
File git_cl.py (right):

https://codereview.chromium.org/16211005/diff/4001/git_cl.py#newcode1756
git_cl.py:1756: elif options.three_way:
I'm fine with adding it as the default without an option to disable it. The tool
should return 1 if there is a merge conflict though. Please test it so that git
cl doesn't stack trace here in that case.

[tapted, 2013-06-06 01:07:05]

Is this what you had in mind?

This preserves the behaviour of --reject, but otherwise makes --3way the default
behaviour. I've checked:
 - applying a patch cleanly goes smoothly, and performs a commit as normal
 - unclean patches resolvable by --3way give EXIT_SUCCESS and do a local commit
 - if conflicts remain, gives an exit status of 1 and does not commit. No
stackdump.
 - If --3way fails completely (e.g. files missing in index), working copy is
unchanged. --reject can still be useful in this case.
 - Behaviour of --reject is unchanged (turns off --3way)

(Updated CL description.)

PTAL

[M-A Ruel, 2013-06-06 20:03:39]

lgtm

[tapted, 2013-06-07 00:12:53]

Committed patchset #3 manually as r204671 (presubmit successful).

[ncarter (slow), 2013-06-07 19:42:00]

https://codereview.chromium.org/16211005/diff/9001/git_cl.py
File git_cl.py (right):

https://codereview.chromium.org/16211005/diff/9001/git_cl.py#newcode1755
git_cl.py:1755: cmd.append('--3way')
FYI: this option doesn't seem to exist in git version 1.7.9.6, which I think is
the version that seems to be on many macs (somebody claimed it gets installed
with xcode). Do we have a minimum git version?

[M-A Ruel, 2013-06-07 19:44:45]

https://codereview.chromium.org/16211005/diff/9001/git_cl.py
File git_cl.py (right):

https://codereview.chromium.org/16211005/diff/9001/git_cl.py#newcode1755
git_cl.py:1755: cmd.append('--3way')
On 2013/06/07 19:42:00, ncarter wrote:
> FYI: this option doesn't seem to exist in git version 1.7.9.6, which I think
is
> the version that seems to be on many macs (somebody claimed it gets installed
> with xcode). Do we have a minimum git version?

Trent, can you revert or fix? We have to support somewhat older versions to a
certain extent.

[tapted, 2013-06-07 23:43:19]

On 2013/06/07 19:44:45, Marc-Antoine Ruel wrote:
> https://codereview.chromium.org/16211005/diff/9001/git_cl.py
> File git_cl.py (right):
> 
> https://codereview.chromium.org/16211005/diff/9001/git_cl.py#newcode1755
> git_cl.py:1755: cmd.append('--3way')
> On 2013/06/07 19:42:00, ncarter wrote:
> > FYI: this option doesn't seem to exist in git version 1.7.9.6, which I think
> is
> > the version that seems to be on many macs (somebody claimed it gets
installed
> > with xcode). Do we have a minimum git version?
> 
> Trent, can you revert or fix? We have to support somewhat older versions to a
> certain extent.

Drat. I'll revert while I track down when this came in.

[tapted, 2013-07-09 01:46:10]

maruel: PTAL. I was inspired to give this another go. This adds a version check
using distutils.version.LooseVersion. Tested with a crusty 1.7.9 I had lying
around in cygwin.

[M-A Ruel, 2013-07-09 13:27:14]

On 2013/07/09 01:46:10, tapted wrote:
> maruel: PTAL. I was inspired to give this another go. This adds a version
check
> using distutils.version.LooseVersion. Tested with a crusty 1.7.9 I had lying
> around in cygwin.

Please create a new CL instead of reusing this one.

https://codereview.chromium.org/16211005/diff/24001/git_cl.py
File git_cl.py (right):

https://codereview.chromium.org/16211005/diff/24001/git_cl.py#newcode11
git_cl.py:11: from distutils.version import LooseVersion
I don't think this exists on Windows.

[tapted, 2013-07-10 01:11:52]

On 2013/07/09 13:27:14, Marc-Antoine Ruel wrote:
> On 2013/07/09 01:46:10, tapted wrote:
> > maruel: PTAL. I was inspired to give this another go. This adds a version
> check
> > using distutils.version.LooseVersion. Tested with a crusty 1.7.9 I had lying
> > around in cygwin.
> 
> Please create a new CL instead of reusing this one.

Created https://codereview.chromium.org/18966004 . I'll publish momentarily and
close this one.

https://codereview.chromium.org/16211005/diff/24001/git_cl.py
File git_cl.py (right):

https://codereview.chromium.org/16211005/diff/24001/git_cl.py#newcode11
git_cl.py:11: from distutils.version import LooseVersion
On 2013/07/09 13:27:15, Marc-Antoine Ruel wrote:
> I don't think this exists on Windows.

All my tests seem happy. I think this is just part of the python standard
library, since 1998 (aka forever). The file history is just whitepsace and
comment tweaks -
http://hg.python.org/cpython/log/b44749cee660/Lib/distutils/version.py

Tested with Python 2.6.2 in cmd.exe . I had to install unixutils and put it in
my path because `git cl patch` runs things through `sed`. There's even a
convenient conflict landed in git_cl.py the last 24 hours to see the 'old'
behaviour.

D:\src\depot_tools>python --version
Python 2.6.2

D:\src\depot_tools>where python
D:\src\depot_tools\python.bat
C:\python_26_amd64\files\python.exe

D:\src\depot_tools>python git_cl.py patch 16211005
Loaded authentication cookies from C:\Users\tapted/.codereview_upload_cookies
error: patch failed: git_cl.py:1757
error: git_cl.py: patch does not apply
Failed to apply the patch

/* rebase at 18966004 */

D:\src\depot_tools>python git_cl.py patch 18966004
Loaded authentication cookies from C:\Users\tapted/.codereview_upload_cookies
Committed patch locally.

D:\src\depot_tools>git cl patch 18966004
Loaded authentication cookies from C:\Users\tapted/.codereview_upload_cookies
error: patch failed: git_cl.py:8
Falling back to three-way merge...
Applied patch to 'git_cl.py' cleanly.
Command "git commit -m patch from issue 18966004" failed.
# On branch master
# Your branch is ahead of 'origin/master' by 1 commit.
#
nothing to commit, working directory clean