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bug#34506: 27.0.50: push-button bug with basic text-property button
From: |
Basil L. Contovounesios |
Subject: |
bug#34506: 27.0.50: push-button bug with basic text-property button |
Date: |
Tue, 19 Feb 2019 03:08:33 +0000 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux) |
Robert Weiner <rsw@gnu.org> writes:
> On Mon, Feb 18, 2019 at 3:51 PM Basil L. Contovounesios <contovob@tcd.ie>
> wrote:
>
> Eli Zaretskii <eliz@gnu.org> writes:
>
> >> From: Robert Weiner <rsw@gnu.org>
> >> Date: Sun, 17 Feb 2019 18:46:09 -0500
> >> Cc: 34506@debbugs.gnu.org
> >>
> >> And what about (button-type (button-at (point))) returning
> >> nil when button-at returns non-nil. Both of these functions
> >> operate on push-buttons as the button.el code reflects, right?
> >> If so, then that should be a bug. If not, then it could use
> >> some explanation.
> >
> > button-type requires a button as an argument, whereas button-at is
> > documented to return a marker for text-buttons. So you cannot safely
> > invoke button-type if the button at point might be of the text-button
> > type.
>
> Buffer positions, markers, and overlays all qualify as "buttons", so
> button-type works with both text- and overlay-buttons (but not widgets).
>
> But as I think I noted in my first message, my recollection
> is that button-type returned nil when given a marker value
> returned from button-at.
I think what's confusing you is that button-at returns a marker even
when there is no button at point. If either of the following two
expressions evaluates to nil, then there is no button at point:
(button-type (button-at (point)))
(button-type (point))
If there is something that *looks* like a button at point, yet these
expressions evaluate to nil, then you're probably looking at a widget
instead.
> Since widgets use text-properties,
AFAICT Customize widgets use overlays, not text properties. I concluded
this by comparing the results of (text-properties-at (point)) and
(overlays-at (point)) with point at a Customize button.
> button-at on a widget can return a non-nil value, so to say that
> widgets and buttons are unrelated ignores the programming API.
Again, that button-at returns a marker for a widget is a coincidence,
not part of either library's API. Last time I read/skimmed the relevant
manuals I was not given the impression that these libraries were
related, but suggestions for clarification of their text is always
welcome.
> Maybe the solution is to add a more opaque programming abstraction
> atop each type so that they don't expose their underlying
> implementations and cause programming errors.
Can you please elaborate? I don't see how either library's
implementation is exposed beyond what is documented in its respective
manual.
> So I'm guessing what you meant is "you cannot safely invoke button-type
> if the button at point might be a widget rather than a button".
>
> Yes, again noting that widget documentation specifically mentions push-buttons
> (push-button is the function used to activate buttons).
push-button is indeed a button.el function used to activate buttons, but
this has nothing to do with the push-button widget type, which is
documented under '(widget) Introduction' and '(widget) push-button'.
> This negates the idea that the two constructs are wholly independent
> of each other.
I hope I have managed to convince you otherwise.
--
Basil
- bug#34506: 27.0.50: push-button bug with basic text-property button, Bob Weiner, 2019/02/16
- bug#34506: 27.0.50: push-button bug with basic text-property button, Eli Zaretskii, 2019/02/17
- bug#34506: 27.0.50: push-button bug with basic text-property button, Eli Zaretskii, 2019/02/18
- bug#34506: 27.0.50: push-button bug with basic text-property button, Basil L. Contovounesios, 2019/02/19
- bug#34506: 27.0.50: push-button bug with basic text-property button, Robert Weiner, 2019/02/20
- bug#34506: 27.0.50: push-button bug with basic text-property button, Basil L. Contovounesios, 2019/02/24