bug#39379: 27.0.60; Fix for #38457 broke ido-vertical-mode

[Dmitry Gutov <dgutov@yandex.ru>]

On 04.02.2020 18:40, Eli Zaretskii wrote:

>> But... the change in ido-vertical-mode is simpler still: just add an
>> extra argument to concat.
> 
> That's true, but AFAIU the problem is not limited to
> ido-vertical-mode, it will happen whenever the string to display
> starts with a newline.  Such a string is entirely legitimate, isn't
> it? And the caller cannot possibly know that ido-exhibit will put the
> 'cursor' property on the first character of that text.  So I think it
> isn't entirely reasonable to expect such callers to defend themselves
> against internal implementation details of ido-exhibit.

Umm, it's ido-exhibit that calls ido-completions. And ido-completions, 
as defined in ido.el, never returns such strings.

Anyway, since you insist, I've pushed that change.

>> If we do that in ido.do, the reason why would be fairly non-obvious from
>> that code.
> 
> If the test for the leading newline is there, the reason is quite
> obvious, and we can have a comment for those who don't know enough
> about the 'cursor' property and cursor positioning.  I think the
> result will more obvious than a mysterious concatenation of a blank in
> ido-vertical-mode, which will need a comment explaining it as well.

Yes, ok. Although our general policy, I think, is that external packages 
that use questionable practices (such as redefining functions, instead 
of using whatever available public customization points there are) are 
generally left to their own devices.