Disallow rendering the same component more than once

[joeldrapper]

Rendering a component more than once can result in unintended consequences. For example, if your component uses DeferredRender to capture slots, the content of those slots will leak between different renders of the same instance.

I think we should update Phlex to disallow this, raising an error if you attempt to render the same instance of a component more than once. The place to do this would be in __final_call__ which is the method that gets renamed to call after the first render for caching.

phlex/lib/phlex/sgml.rb

Lines 97 to 127 in 6a0eb85

	def __final_call__(buffer = +"", context: Phlex::Context.new, view_context: nil, parent: nil, &block)
	@_buffer = buffer
	@_context = context
	@_view_context = view_context
	@_parent = parent
	block ||= @_content_block
	return "" unless render?
	around_template do
	if block
	if is_a?(DeferredRender)
	__vanish__(self, &block)
	template
	else
	template do |*args|
	if args.length > 0
	yield_content_with_args(*args, &block)
	else
	yield_content(&block)
	end
	end
	end
	else
	template
	end
	end
	buffer << context.target unless parent
	end

I would approach this by first checking for an instance variable and raising if it's true, and then setting that instance variable to true.

[joeldrapper]

We can add this as a warning in 1.x.