Merge ~lutostag/layer-snap:revision_arg into ~stub/layer-snap:master

[Greg Lutostanski]

Allow a revision arg.

I am planning on making a small snap-action layer that will allow users to install specific revisions of snaps.

Essentially this is so that OIL can change juju snap revisions on demand via an action.

I thought this might be an addition to the base snap-layer that others may want in the future.

Thanks!

[Stuart Bishop (stub)]

Yes, we need this.

I'll update the docs to match.

review: Approve

diff --git a/lib/charms/layer/snap.py b/lib/charms/layer/snap.py
index b2fc2b9..0ab005a 100644
--- a/lib/charms/layer/snap.py
+++ b/lib/charms/layer/snap.py
@@ -105,7 +105,7 @@ def connect_all():
 
 def _snap_args(channel='stable', devmode=False, jailmode=False,
                dangerous=False, force_dangerous=False, connect=None,
-               classic=False):
+               classic=False, revision=None):
     if channel != 'stable':
         yield '--channel={}'.format(channel)
     if devmode is True:
@@ -116,6 +116,8 @@ def _snap_args(channel='stable', devmode=False, jailmode=False,
         yield '--dangerous'
     if classic is True:
         yield '--classic'
+    if revision is not None:
+        yield '--revision={}'.format(revision)
 
 
 def _install_local(path, **kw):