Middleware mutex class

[technoweenie]

This extracts the Faraday::MiddlewareRegistry module functionality into a Faraday::ClassRegistry class. This allows us to make some better assumptions about how the class registry's internal vars are loaded.

TODO:

• copy/adapt MiddlewareRegistry specs for ClassRegistry
• test with technoweenie/faraday-live

I also made a few small changes that may bite us later:

1. Deprecated #load_middleware. It's the same as #lookup_middleware, except #lookup_middleware raises if it doesn't return anything. When deciding between ClassRegistry#lookup and #load, I went with #lookup since #load is an existing ruby method.

faraday/lib/faraday/middleware_registry.rb

Lines 207 to 214 in 1c5672a

	def lookup_middleware(key)
	class_registry.lookup(key)
	end
	def load_middleware(key)
	warn "Deprecated, use #{self}.lookup_middleware"
	lookup_middleware(key)
	end

2. Deprecated #middleware_mutex and #fetch_middleware. Those should've been private originally. They're not used elsewhere in Faraday, but may be in use in an external lib or app. Pretty low chance though...

faraday/lib/faraday/middleware_registry.rb

Lines 216 to 222 in 1c5672a

	def middleware_mutex
	warn "Deprecated, see #{self}.class_registry"
	end
	def fetch_middleware(_)
	warn "Deprecated, see #{self}.class_registry"
	end

3. #register_middleware now complains if you try to change the autoload_path _after the ClassRegistry has been setup`. So, something like:

module Faraday
  class Adapter
    extend MiddlewareRegistry

    # first time, set 'path/to/adapters' as @autoload_path
    register_middleware 'path/to/adapters', foo: Foo

    # subsequent calls MUST ignore @autoload_path
    register_middleware bar: Bar

    # raises a warning: 
    # "Cannot change autoload_path of existing Faraday::Adapter.class_registry"
    register_middleware 'path/to/other-adapters', baz: Baz
  end
end

faraday/lib/faraday/middleware_registry.rb

Lines 173 to 175 in 1c5672a

	unless autoload_path.nil?
	warn "Cannot change autoload_path of existing #{self}.class_registry"
	end