bug#36459: 27.0.50; octave-mode ElDoc support bug

[Dmitry Gutov <dgutov@yandex.ru>]

On 09.07.2019 1:28, Mauro Aranda wrote:
> Leo Liu <sdl.web@gmail.com <mailto:sdl.web@gmail.com>> writes:
> 
> Hello Leo.  Thanks for your answer.
> 
>  > Can this bug be fixed by changing the regexp in
>  > `octave-eldoc-function-signatures' from
>  >
>  >         "\\s-*\\(?:--[^:]+\\|usage\\):\\s-*\\(.*\\)$"
>  >
>  > to
>  >
>  >         "\\s-*\\(?:--[^:]+\\|\\_<usage\\):\\s-*\\(.*\\)$"
>  > ?
> 
> Yes, indeed, this change fixes it.  Will you push the fix?

I've tried to verify the fix myself, and foremost to see whether the 
cases where ElDoc should be displayed still work.

But I haven't managed to find working ones, with either version of the 
regexp. My Octave version is 4.2.2.

The output of e.g. print_usage ('abs') is:

   error: Invalid call to abs.  Correct usage is:

    -- abs (Z)

   Additional help for built-in functions and operators is
   available in the online version of the manual.  Use the command
   'doc <topic>' to search the manual index.

Neither regexp seems to match the second line.

Ideas? Are there help outputs that do match? Is 4.2.2 too new/too old?