bug#41198: bug#41130: bug#41198: 27.0.60; [PATCH] heading cycling command for outline

[Yuan Fu <casouri@gmail.com>]

> On Oct 17, 2020, at 4:30 PM, Juri Linkov <juri@linkov.net> wrote:
> 
>>> +  (condition-case nil
>>> +      (pcase (outline--cycle-state)
>>> +        ('hide-all
>>> +         (if (outline-has-subheading-p)
>>> +             (progn (outline-show-children)
>>> +                    (message "Only headings"))
>>> +           (outline-show-subtree)
>>> +           (message "Show all")))
>>> +        ('headings-only
>>> +         (outline-show-subtree)
>>> +         (message "Show all"))
>>> +        ('show-all
>>> +         (outline-hide-subtree)
>>> +         (message "Hide all")))
>>> +    ;; If error: "Before first heading" occurs, ignore it.
>>> +    (error nil)))
>> 
>> This is basically an `ignore-errors' around a whole bunch of code, used
>> as a program flow mechanism, and that's always awkward, because it hides
>> real errors in the code.
>> 
>> Altering the functions to not error out in these situations would be
>> better.
> 
> Like 'outline-back-to-heading' has an optional argument 'invisible-ok',
> maybe a new argument named 'error-ok' or 'outside-ok' could
> be added to not error out when point is outside of the outline tree.

I can modify outline code to signal a signal (say ‘outline-before-first-heading) rather than an error, and handle that signal specifically. How’s that?

Yuan