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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 15:26:59 +0000 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux) |
Eli Zaretskii <eliz@gnu.org> writes:
>> From: "Basil L. Contovounesios" <contovob@tcd.ie>
>> Cc: <rswgnu@gmail.com>, <34506@debbugs.gnu.org>
>> Date: Mon, 18 Feb 2019 20:51:12 +0000
>>
>> 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".
>
> No, I'm trying to explain why button-type returns nil in the case of
> text-buttons.
I'm sorry if I've misunderstood something obvious, but button-type
should never return nil for any kind of button.el button, regardless of
whether it's a text or overlay button.
As stated in '(elisp) Button Types', "every button has a button type".
For example, the following should return 'button:
(with-temp-buffer
(let* ((tstart (prog1 (point) (insert-text-button "text")))
(ostart (prog1 (point) (insert-button "overlay")))
(tbutton (button-at tstart))
(obutton (button-at ostart))
(ttype (button-type tbutton))
(otype (button-type obutton)))
(cl-assert (and tbutton obutton ttype otype))
(cl-assert (eq ttype otype))
(cl-assert (eq ttype (button-type tstart)))
(cl-assert (null (button-type ostart)))
ttype))
[ By the way, would something like this be welcome as a start for
test/lisp/button-tests.el? ]
The only cases (within reason) in which button-type may return nil are:
0. button-type is mistakenly given a buffer position POS instead of an
overlay when the button at POS is an overlay (not text) button, as
shown in the example above. Using (button-at POS) avoids this
problem.
1. button-type is given the value of a widget's (not button's) 'button
overlay property. This is not that far-fetched since both libraries
rely on (get-char-property POS 'button), but I don't see why anyone
would mix widgets and buttons in the same buffer and run the risk of
such gotchas. I believe this contributed in part to Robert's
confusion.
Am I missing something?
--
Basil
- bug#34506: 27.0.50: push-button bug with basic text-property button, (continued)