> ASDF checks to make sure all of the initargs are defined when parsing a > `defsystem`. This is good for catching errors, but is terrible for > extensibility. This means that any attempt to add additional metadata will be > backwards incompatible.
> I can think of two ways to fix this: > 1. Add a "garbage can" slot to `component` that will be filled with a > property list, and allow programmers to do whatever they want here. This > doesn't seem great to me. > 2. Add a new `defsystem` parsing error class that is > `unknown-component-property`, raise it when an unknown property is > encountered and allow the user to continue, discarding the initarg and > accompanying value. > The second alternative is what I favor. It isn't great, because it will only > maintain extensibility going forward, but I think it's the best we can do. How can ASDF or a developer determine that the unknown property doesn't change the semantics of the DEFSYSTEM, and therefore discarding it would have an effect that's contrary to the author's intention ? ASDF has no syntactic distinction between properties that affect the compilation process and mere annotations like author, licence, etc... > I suppose that we could also add an initarg to tell ASDF to continue such > errors silently. > I'd be inclined to suggest that this take an ASDF version expression as > value, so that the error is quietly ignored only by ASDF versions below that. > This means that the property will start to be checked when it has become > authoritative. > Note that for one's own `system` and `component` subclasses, the set of > initargs can be extended without any monkeying around. This is a recipe for maintenance nightmares. Let's not go there. -- Stelian Ionescu
