bug#36550: mouse-face overlay calculation error

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

> Mouse-face isn't supposed to cover newlines, I think.  Why do you need
> that?

Because Widget wants to have the mouse-face extend to the end of the
line, I think...

> The "one character shorter" variant does what it's expected to do,
> because mouse-face is not extended to EOL as with other faces.
> Mouse-face is for showing the parts of text that are mouse-sensitive,
> so it makes no sense to highlight portions of display that have no
> text.

OK, if this is how mouse-face is supposed to work, then the fix in
wid-edit.el should be pretty trivial -- I'll just have it not put the
overlay on the newline?

>> So is there some basic fault in the code that calculates the length of
>> the mouse highlighting?  I don't really know where to start looking...
>
> It's in the display code, and is quite complicated due to
> bidirectional text use case.  See mouse_face_from_buffer_pos and its
> subroutine rows_from_pos_range.

Oh, wow; that's a daunting function indeed...

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