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

[Lars Ingebrigtsen]

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?

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