[PATCH 4 of 4 accept-scripts] land: fix JSON error when no accepted changes to land

[Augie Fackler]

LGTM, please deploy to end the torrent of cron mail ;)

> On May 2, 2018, at 16:31, Kevin Bullock <kbullock+mercurial at ringworld.org> wrote:
> 
> # HG changeset patch
> # User Kevin Bullock <kbullock at ringworld.org>
> # Date 1525292842 18000
> #      Wed May 02 15:27:22 2018 -0500
> # Node ID bafcc443cd52382c574822bd4fef2f83141b10e1
> # Parent  335d45810dd93321242e7c329cf6d603a3aa7516
> land: fix JSON error when no accepted changes to land
> 
> diff --git a/land b/land
> --- a/land
> +++ b/land
> @@ -50,6 +50,9 @@ all_accepted = [n for n in cq.draft() if
> acceptrange = collections.namedtuple('acceptrange', 'roots head')
> 
> def accepted_ranges(all_accepted):
> +    if not all_accepted:
> +        return []
> +
>     accepted_revset = ' + '.join(all_accepted)
>     info = json.load(os.popen("hg log -R %s -r '%s' -Tjson" % (
>         conf.source, accepted_revset)))
> diff --git a/tests/test-land.t b/tests/test-land.t
> --- a/tests/test-land.t
> +++ b/tests/test-land.t
> @@ -1,22 +1,6 @@
>   $ . "$TESTDIR/lib.sh"
> -BUG: Fails with no accepted nodes to land.
> +Works correctly with no accepted nodes to land.
>   $ land
> -  hg: parse error: empty query
> -  Traceback (most recent call last):
> -    File "/Users/kbullock/Source/Projects/hg/accept/tests/../land", line 87, in <module>
> -      for r in accepted_ranges(all_accepted):
> -    File "/Users/kbullock/Source/Projects/hg/accept/tests/../land", line 53, in accepted_ranges
> -      conf.source, accepted_revset)))
> -    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/__init__.py", line 290, in load
> -      **kw)
> -    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/__init__.py", line 338, in loads
> -      return _default_decoder.decode(s)
> -    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/decoder.py", line 366, in decode
> -      obj, end = self.raw_decode(s, idx=_w(s, 0).end())
> -    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/decoder.py", line 384, in raw_decode
> -      raise ValueError("No JSON object could be decoded")
> -  ValueError: No JSON object could be decoded
> -  [1]
> 
> If only r2 is accepted, nothing happens.
>   $ echo `hg log -r 2 -R source --template '{node}'` > bob-accepted