RE: `interactive-form` symbol property (was: [Emacs-diffs] emacs-26 9a53b6d: Say how to override a primitive interactive spec)

[Drew Adams <drew.adams@oracle.com>]

> >> +If you wish to override a primitive interactive specification, just
> >> +set the @code{interactive-form} property of the primitive function's
> >> +symbol (@pxref{Using Interactive}).  There is no need to edit C code
> >> +and recompile Emacs.
> > You can also use advice-add for the same purpose (it's more
> > complicated, but it's arguably better behaved).
> 
> And a quick search seems to indicate that this `interactive-form`
> property is not used anywhere (not within Emacs, not within GNU ELPA,
> and not within the few other Elisp packages I had lying around for
> a quick search).
> 
> Maybe, rather than document it, we should obsolete it?

Why?  Is the existence of this property causing some problem?

Seems like it could be useful (and simple to use) in code
generation or manipulation.  You can't advise a function
that doesn't exist yet.

(To be clear, I haven't used this property.  I have used
the function of the same name, however.)

---

BTW, in the Elisp manual we have 2 index entries for this,
with pretty much the same text (shared prefix) and different
targets.  If we want two entries, for the different targets,
perhaps the entries should not be so similar?

* interactive-form property:         Defining Commands.   (line  16)
* interactive-form, symbol property: Using Interactive.   (line  21)

There is even a third entry, which might appear to fall into
the same boat, but it in fact refers to the function of the
same name:

* interactive-form:                  Using Interactive.   (line 129)

If we want to distinguish function from property in the index
entries, then perhaps the function entry should be something
like `interactive-form, function'.