Re: Is this a bug in overlay property list handling?

[Lennart Borgman (gmail)]

Stefan Monnier wrote:
> > I am not sure if I have hit a bug or if I am doing something wrong. I do
> > something like this in my code:
>
> >   (setq syntax-ppss-last-min
> >         (copy-tree
> >          (cons (1- last-pos)
> >                (if is-main-mode-chunk
> >                    (mumamo-with-major-mode-fontification main-major
> >                      `(parse-partial-sexp (point-min) last-pos))
> >                  (parse-partial-sexp 1 1)))
> >          ))
> >   (overlay-put chunk-at-pos 'syntax-ppss-last-min syntax-ppss-last-min)
>
> > If I test this immediately after with `overlay-get' the value looks ok.
>
> > However, later when I read these values with `overlay-get' it seems like the
> > property list has got corrupted. The car of the value stored in property
> > syntax-ppss-last-min is nil.
>
> > I use copy-tree to try to avoid surprices like this one.
>
> The `cons' already makes sure you have the only reference to the object
> and parse-partial-sexp also returns a fresh value, so the `copy-tree' is
> not needed.

Thanks for the explanation.

> > Maybe I should do something different? Maybe this is a bug in overlay
> > property list handling?
>
> I'd be very surprised if it's a bug in overlay property handling.
> My guess is that it's a bug elsewhere in your code.

Ok, this should make it easier to find this bug.


>         Stefan
>
>
> PS: BTW, please avoid using `1' instead of (point-min), or else add
> a comment explaining why (point-min) is not right.

I will add a comment.

> Also the
> `(parse-partial-sexp (point-min) last-pos) looks odd: you probably
> forgot a comma before `last-pos'.

Yes, I did. Thanks.

> Maybe mumamo-with-major-mode-fontification should be a macro rather than
> a function.

I am not sure now. I will have a look again.