ActiveSupport expects a hash as a payload for notifications

[workmad3]

ActiveSupport expects a hash to be passed as the payload to instrument. In the majority of cases, not passing a hash doesn't cause any incorrect behaviour.

However, if the block passed to instrument raises an Exception, ActiveSupport::Notifications will attempt to add an :exception key to the payload hash. When this occurs within a cache fetch for ReadThis, the end result is a TypeError from deep inside the cache code, unrelated to the original exception. (https://github.com/rails/rails/blob/30af171af13293aa37bee612ae7b976d3ede0439/activesupport/lib/active_support/notifications.rb#L64)

(credit goes to @banister for figuring out this edge case)

[sorentwo]

Awfully the spec for notifications passes a hash rather than the single key. Unfortunately the instrument block itself isn't tested by the cache spec, so this wasn't caught. Thanks for the patch, it's appreciated.

Will you add an entry to the CHANGELOG and give yourself credit please?

[workmad3]

No worries, we just happened to discover this when figuring out problems with a mis-behaving redis instance, and @banister took the time to dig into the odd TypeError exceptions we were getting.

Hopefully the CHANGELOG entry is ok.

[sorentwo]

Looks great. Perfect.