Ability to set anonymousId removed in 3.6.0

[jonah-williams]

I stumbled across an unexpected change in behavior after upgrading across 3.6.0.

In 3.5.7...3.6.0#diff-90ee8062efa95f661137bf2685fd0256L271 we can see that identify started constructing a SEGIdentifyPayload with a nil anonymousId (and that remains true today in https://github.com/segmentio/analytics-ios/blob/master/Analytics/Classes/SEGAnalytics.m#L203) We used to be able to specify an anonymous id in the options argument.

https://github.com/segmentio/analytics-ios/blob/master/Analytics/Classes/Integrations/SEGIntegrationsManager.m#L155 appears to retain some of this behavior which checks SEGIdentifyPayload.options but that can now only ever contain context and integrations keys via https://github.com/segmentio/analytics-ios/blob/master/Analytics/Classes/Integrations/SEGIntegrationsManager.m#L526

I had found the option to specify an anonymous id useful because it allowed me to keep identifiers for crash logging and analytics in sync so I could correlate them as needed. In my case I can switch to allowing Segment to be the authority over my anonymous ids but maybe there should be some option to explicitly set this value, either via identify or otherwise?

[f2prateek]

Ah yep, this looks like a bug as part of the middleware changes. I think the fix should be to move that logic from SEGIntegrationsManager upto `SEGAnalytics.

[f2prateek]

I don't have an ETA, but I've triaged the issue internally in our JIRA https://segment.atlassian.net/browse/LIB-266