Merge ~xavpaice/layer-snap:bug/1919246 into ~stub/layer-snap:master

[Xav Paice]

[Xav Paice (xavpaice)]

Cory - I need to understand better the reason that 'hookenv.atstart(check_refresh_available)' was added in 2d3872544653c2fcec4a9b57d594d976b7fd1042 (Add support for snap coherence) and if we can avoid running the refresh check every hook execution.

[Cory Johns (johnsca)]

It was added to support handlers being triggered (via a flag) when a snap had a pending refresh available. The primary use-case was to allow for a cohort manager, such as kubernetes-master, to check whether any of the cohorts it was managing had updates [1]. However, it was subsequently realized [2] that using `snap refresh --list` doesn't work if the cohort manager is managing snaps that it doesn't have installed itself, and so we're no longer using it. If there's no other need to trigger handlers based on pending refreshes (and I can't think of any others), then I think it's fine to remove it.

[1]: https://github.com/charmed-kubernetes/charm-kubernetes-master/pull/61
[2]: https://github.com/charmed-kubernetes/charm-kubernetes-master/pull/125

review: Approve

[Stuart Bishop (stub)]

If charms turn out to be using this, they can temporarily add back the hookenv.atstart(check_refresh_available) call themselves and we can revisit their use case.

review: Approve

diff --git a/reactive/snap.py b/reactive/snap.py
index 557eb84..1fda7b7 100644
--- a/reactive/snap.py
+++ b/reactive/snap.py
@@ -105,6 +105,7 @@ def refresh():
     # It probably should live in the base layer, blocking the charm
     # during bootstrap if the arch is unsupported.
     arch = uname()[4]
+    check_refresh_available()
     for snapname, snap_opts in opts.items():
         supported_archs = snap_opts.pop("supported-architectures", None)
         if supported_archs and arch not in supported_archs:
@@ -346,4 +347,3 @@ hookenv.atstart(ensure_path)
 hookenv.atstart(update_snap_proxy)
 hookenv.atstart(configure_snap_store_proxy)
 hookenv.atstart(install)
-hookenv.atstart(check_refresh_available)