bug#40919: 27.0.91; next-error-select-buffer does not always behave as documented

[Juri Linkov <juri@linkov.net>]

> The next-error-select-buffer documentation states that “the selected
> buffer becomes the source of locations for the subsequent invocation of
> ‘next-error’ or ‘previous-error’.” However, it is not the case for the
> following:
>
> 1. Go in a fresh next-error capable buffer (not *grep*).
> 2. Grep for something.
> 3. M-x next-error-select-buffer *grep*
> 4. M-x next-error
>
> The buffer of 1 (not *grep*) is the source of locations instead of
> the expected *grep*.
>
> This is because although next-error-select-buffer sets the variable
> next-error-last-buffer, it is not used in this case: When next-error
> calls next-error-find-buffer, next-error-buffer has no buffer-local
> value yet, so condition 2. in next-error-find-buffer (that
> next-error-buffer has no buffer-local value and the current buffer is a
> next-error capable buffer) is true, and the function never even checks
> next-error-last-buffer.

Thanks for the report.  Do you think the problem is in implementation,
or only in documentation?  IOW, do you think its behavior is correct,
but the documentation should be fixed to describe more clearly what
next-error was intended to do in this situation?