Use smarter type detection for AssignableTypes

[stevenleeg]

Hi there,

This PR stems from an issue I've asked about in Gitter but didn't end up with a response, so I figured I'd submit the fix myself.

When developing agents locally and importing them via the ADDITIONAL_GEMS=some_agent(path:../some_agent) pathway, I noticed that any agents within the gems wouldn't end up in the agents list of the agent creation page. Doing some digging, I found that the reason was that the dropdown was being populated, via various layers of the stack, by this line in assignable_types.rb:

const_set(:TYPES, Dir[Rails.root.join("app", "models", module_name.underscore, "*.rb")].map { |path| module_name + "::" + File.basename(path, ".rb").camelize })

Searching through the app/models/agents directory naturally omits agents provided by gems, as they're stored not only outside of that directory, but even outside of the Huginn project root. This PR fixes this by populating the TYPES constant with the actual list of constants contained by the namespace at runtime.

The one thing I'm a little stumped on is how this list ends up getting populated properly (ie including agens in gems) when in production, as this is an issue I've only been able to replicate on my development instance. Perhaps there's something I'm missing here, but otherwise this seems like a pretty straightforward fix.

[knu]

I'm afraid this may not work in development and test environments where files are lazy-loaded. Can you confirm this works even in development mode? (e.g. bundle exec rails r 'puts Agent::TYPES')