Context

When the new plugin system was put in place, it was important to keep the bot's interface as backward compatible as possible, and we did a pretty good job. Now it is time to think about the future, and remove the leftovers. For instance, the registration (and removal) of a plugin is a complex sequence:

• the bot in its setup phase, calls setup_plugins to register and loads its plugins
• this setup_plugins method calls the handler's register method (and provide the bot itself as argument)
• this register method calls loader.clean_module, which does a bunch of stuff we should not need, but for now we do
• then it calls bot.add_plugin, circling back to the bot...

This issue is a follow-up on #2341 that adds TODO to remove add_plugin and remove_plugin.

Problems & Solutions

The problem is that bot.add_plugin must have the same input as the output of loader.clean_module, and adding any new type of plugin callables is more difficult because of that. Since the bot already has a bunch of specific register_* methods:

self.register_callables(callables)
self.register_jobs(jobs)
self.register_shutdowns(shutdowns)
self.register_urls(urls)

we could reuse these directly. All that is left is to register the plugin handler itself (self._plugins[plugin.name] = plugin) which can be done directly by the setup_plugins method.

And then, we can deprecate add_plugin, do the same thing for remove_plugin, and probably clean up some other things along the way (I'm looking at you, sopel.loader).

Planning

• Replace add_plugin and remove_plugin by direct call to specific registration methods (see bot, plugins: deprecate bot.{add|remove}_plugin #2636)
• deprecate both in Sopel 8.1, to be removed in Sopel 9 (see bot, plugins: deprecate bot.{add|remove}_plugin #2636)

Removing the deprecated method will be done in #2640