bug#35397: flyspell-mode affects delete-selection-mode

bug#35397: flyspell-mode affects delete-selection-mode

[Евгений Курневский]

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Emacs version: 26.2
Steps to reproduce:
emacs -Q
M-x delete-selection-mode
M-x flyspell-mode
Type one word, select it and type one character. This character will be
selected for flyspell-delay seconds.
Desired behavior - selection disappears right after new character is
inserted, as without flyspell-mode.

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bug#35397: flyspell-mode affects delete-selection-mode

[Stefan Kangas]

Евгений Курневский <kurnevsky@gmail.com> writes:

> Emacs version: 26.2
> Steps to reproduce:
> emacs -Q
> M-x delete-selection-mode
> M-x flyspell-mode
> Type one word, select it and type one character. This character will be selected for flyspell-delay seconds.
> Desired behavior - selection disappears right after new character is inserted, as without flyspell-mode.

I tried the following steps:

0. emacs -Q
1. M-x delete-selection-mode
2. M-x flyspell-mode
3. foobar C-SPC C-a x

What I see is that "x" is highlighted for flyspell-delay seconds.  If I
continue typing before that, the highlighting immediately disappears.
If I type "1" instead of "x", there is no highlighting.

Crucially, the "x" does not get replaced by subsequent characters, as it
would have been under delete-selection-mode if the "x" was actually
selected.  In other words, if you change step three to:

3. foobar C-SPC C-a xyz

You see a buffer containing "xyz".

Thus, the problem seems to be the highlighting only, which could perhaps
be somewhat confusing to a user.  I think this is indeed a bug (or
buglet), although its mostly cosmetic.

Could you please confirm this, or are you talking about something else?

Thanks,
Stefan Kangas

bug#35397: flyspell-mode affects delete-selection-mode

[Евгений Курневский]

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Yes, you are right, the problem is with highlighting. But there is another
undesired consequence - flyspell mode prevents `company` popup in this
case, it appears only after second character is typed. I investigated it a
bit and it seems it's caused by `sit-for` used inside
`flyspell-check-word-p`. So I came up with a workaround that solves both
these issues:

(advice-add 'flyspell-check-word-p :around (lambda (orig-fun &rest args)
                                             (if (eq this-command
'self-insert-command)
                                               (memq
(get-char-code-property (char-before) 'general-category) '(Zs Zl Zp))
                                               (apply orig-fun args))))

This makes flyspell return immediately when `self-insert-command` was used.

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