Unable to load upgraded collector with reduced set of metrics

[marcintao]

When new version of collector is exposes a reduced set of metrics (doesn't export them from GetMetricTypes()) , it's impossible to restart a task involving that collector. Snap will complain about missing metric during task creation, even though:

• task was removed,
• plugin was unloaded and loaded in new version (with version number changed),
• list of metrics reflects tracks the current state of plugins.

OS Version: Ubuntu 16.04
Snap version: snapd version master-cc4eda7 (tip of master)

Steps to reproduce:

• start snap
• load a mock collector (snap-collector-mock1) and file collector,
• start a task involving mock collector,
• verify list of metrics,
• stop 'n' remove the task,
• unload mock1 plugin,
• load 'upgraded' mock1 plugin (missing metric /intel/mock/foo),
• start a task involving mock1.

Actual results:

• task fails to load due to missing metric /intel/mock/foo

Expected results:

• task starts successfully

Complete report of activity:
bug_upgrading_log.txt

[geauxvirtual]

Can you add the task manifest you were using to this issue?

[marcintao]

Added task manifest:
bug_task.txt

[andrzej-k]

Closing - fixed by #1146