bug#22957: C-u C-x = prints garbage for a text property with value '(string . ?")

[Alan Mackenzie <acm@muc.de>]

Hello, Lars.

On Mon, Jul 29, 2019 at 15:09:10 +0200, Lars Ingebrigtsen wrote:
> Alan Mackenzie <acm@muc.de> writes:

> > Hello, Emacs.

> > In the master branch:
> >   emacs -Q
> > .
> > In the *scratch* buffer, with point at any character, do:

> >   M-: (put-text-property (point) (1+ (point)) 'asdf '(string . ?\"))

> > .  Without moving point,

> >   C-u C-x =

> > .  There appears in the *Help* buffer the following:

> >   There are text properties here:
> >     asdf                 string (widget)Top
> >     face                 font-lock-comment-face
> >     fontified            t

> > .  The entry for "asdf" is garbage.  It should show the actual value of
> > the text property just set, not "string (widget)Top".  The same thing
> > happens in Emacs 24.5 (and presumably the emacs-25 branch).

> Indeed.

> > Initial investigation:

> > The symbol 'string has a 'widget-type property.  Without validating the
> > structure (or lack thereof) of the assumed widget value,
> > `describe-property-list' attempts to enter the "widget browser" rather
> > than printing the full value of the 'asdf text property.

> `describe-property-list' is a very general-sounding function, and
> doesn't mention anything about widgets, so having it do widget stuff is
> rather surprising.

> The only callers to this function are from descr-text and as far as I
> can tell, none of them are widget-ey.  Looking at the commit log, it
> looks like there was a bunch of widget stuff in here before, but it's
> been removed.  Perhaps this was just forgotten?

> The following trivial patch fixes the problem.  Any opinions?

It does indeed fix the problem.  I haven't tracked down anything in the
commit log, but I can believe there's no widget stuff left to drive that
cond arm.  And even if there were, it would only be a corner case (like
the original bug scenario was).

I feel only a slight unease at removing that cond arm, which would no
doubt dissipate if I took more time to look at it again.

So, I would agree with you: apply the patch and close the bug.  :-)

> diff --git a/lisp/descr-text.el b/lisp/descr-text.el
> index 8be2b94458..ba53aeb385 100644
> --- a/lisp/descr-text.el
> +++ b/lisp/descr-text.el
> @@ -88,8 +88,6 @@ describe-property-list
>  	     (insert-text-button
>  	      (format "%S" value)
>  	      'type 'help-face 'help-args (list value)))
> -            ((widgetp value)
> -	     (describe-text-widget value))
>  	    (t
>  	     (describe-text-sexp value))))
>      (insert "\n")))


> -- 
> (domestic pets only, the antidote for overdose, milk.)
>    bloggy blog: http://lars.ingebrigtsen.no

-- 
Alan Mackenzie (Nuremberg, Germany).