bug#21072: Brave new mark-defun (and a testing tool)

[npostavs]

Marcin Borkowski <mbork@mbork.pl> writes:

>
> OK, I pushed the branch "fix-bug-21072".  Can anyone confirm that it's
> ok and either merge it into master or tell me that I can do it?

>
> +** New macro 'elisp-tests-with-temp-buffer'
> +which helps writing tests for functions that should change buffers in
> +specific ways or manipulate point or mark positions.
> +
> +---

I don't this should be documented in NEWS since the macro is being added
to a test file, so it's not part of Emacs' libraries.  Also, the format
of the NEWS entry is wrong in the same way as the next one (see below).

> +With a prefix argument, it marks that many defuns or extends the
> +region by the appropriate number of defuns.  With negative prefix
> +argument it marks defuns in the opposite direction and also changes
> +the direction of selecting for subsequent uses of @code{mark-defun}.

This doesn't say what exactly happens with zero as argument.  The code
seems to do something odd.  Perhaps it should just be a user-error
instead?  Or maybe just a nop.

> modified   etc/NEWS
> @@ -363,6 +363,15 @@ words where first character is upper rather than title 
> case, e.g.,
>  "DŽungla" instead of "Džungla".
>  
>
> +** New behavior of 'mark-defun' implemented
> +Prefix argument selects that many (or that many more) defuns.
> +Negative prefix arg flips the direction of selection.  Also,
> +'mark-defun' between defuns correctly selects N following defuns (or
> +-N previous for negative arguments).  Finally, comments preceding the
> +defun are selected unless they are separated from the defun by a blank
> +line.
> +
> ++++
> * Changes in Specialized Modes and Packages in Emacs 26.1
> 

This entry should go before the page separator, and the "+++" should go
on the line just above the entry, not after it.

> +(defun beginning-of-defun-comments (&optional arg)

> +  (let (nbobp)
> +    (while (progn
> +             (setq nbobp (zerop (forward-line -1)))
> +             (and (not (looking-at "^\\s-*$"))
> +                  (beginning-of-defun--in-emptyish-line-p)
> +                  nbobp)))
> +    (when nbobp
> +      (forward-line 1))))


The looking-at call is redundant, right?  Anyway, can't that all be
replaced by just

    (forward-comment (- (point)))
    (unless (bolp)
      (forward-line 1))

> +(defun mark-defun (&optional arg)

> +  (let (nbobp)
> +    (while (progn
> +             (setq nbobp (zerop (forward-line -1)))
> +             (and (looking-at "^\\s-*$")
> +                  nbobp)))
> +    (when nbobp
> +      (forward-line 1))))

I think this can be just

    (skip-chars-backward "[:space:]\n")
    (unless (bolp)
      (forward-line 1))