slot-value-using-class to mark deprecated methods and add more metadata in general?

[aartaka]

Maybe add a slot-value-using-class method for deprecated slots that warns the user on each read/write. Or maybe just on the first one.

Originally posted by @Ambrevar in #2978 (comment)

[jmercouris]

Hm, very interesting idea. Very interesting...

[Ambrevar]

Something signaled by @aadcg is that before releasing 4.0 we should grep all the "Deprecated ... Remove with 4.0".

[Ambrevar]

Something else that could help with deprecated functions / methods:

(uiop:with-deprecation ((uiop:version-deprecation (asdf:system-version :nyxt)
                                                  :style-warning "3.2"
                                                  :warning "3.4"))
  (defun foo ()
    "Foo docstring"
     17))

We could probably leverage this to deprecate slots via MOP.

[aartaka]

So what UIOP uses is compiler macros. Which is easy: generate a compiler macro around the accessor generic function and signal the error there:

(define-compiler-macro ACCESSOR (&whole whole object)
  ;; Check for the type to avoid signaling deprecation for unaffected
  ;; accessors. FIXME: allows only one deprecation per accessor (=
  ;; only one of (name buffer) and (name window) would signal
  ;; deprecation if both are marked as deprecated here)...
  (when (typep object 'CLASS)
    ;; Useful for debugging, given the notoriously opaque macro
    ;; expansion mechanisms.
    (let ((form ',whole))
      ;; Should it be an `error'? UIOP does warnings on minor versions
      ;; and errors on major versions. But Nyxt handles lots of errors
      ;; gracefully enough by ignoring them.
      (error
       ;; We have to write this `deprecated' condition ourselves.
       'deprecated :version VERSION :form form :text "Deprecated in favor of NEW-ACCESSOR."))))

This approach is safe to use in nclasses, for example.

EDIT: unfinished sentence.

[Ambrevar]

But that would fail if there is no accessor or if slot-value is used.
Instead would could leverage slot-value-using-class to ensure the deprecation message is printed.
That said, we almost never export slots without accessors, so it's not so important for the users. The point of using slot-value-using-class is that it triggers a warning even for core devs.

[aartaka]

That said, we almost never export slots without accessors, so it's not so important for the users.

Yes, so we can go with a simpler solution before getting to heavy MOP artillery :P

The point of using slot-value-using-class is that it triggers a warning even for core devs.

Yes, that's a benefit, but the point above kinda makes it overkill :)

[Ambrevar]

The MOP based approach is trivial to implement though with https://github.com/some-mthfka/slot-extra-options, it's just

• One "extra option" declaration,
• One slot-value-using-class specialization against user-classes.