bug#12801: 24.3.50; `scroll-conservatively' and `scroll-step'

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 4 Nov 2012 22:24:53 +0100
> From: Dani Moncayo <dmoncayo@gmail.com>
> 
> 1. Set the variable `scroll-step' to 3.
> 2. Visit the attached file.
> 3. Adjust the vertical space (empty lines) between "first line" and
> "last visible line" until the latter becomes indeed the last visible
> line in the window.
> 4. Move point to the "last visible line".
> 5. Move point two lines down in a single command: C-u 2 C-n
> 
> I observe that after step #5 the window is scrolled by `scroll-step'
> lines (3 lines), which is TRT.
> 
> But if I set `scroll-conservatively' to 1 and repeat the experiment
> (from step #4), then I observe that this time the line where point
> goes to ("2") is centered in the window.
> 
> After reading (info "(emacs) Auto Scrolling"), I think that this is
> either a bug in the program or in the documentation.  This paragraph
> in particular doesn't match the observed behavior in the second case:
> 
>      The variable `scroll-step' determines how many lines to scroll the
>   window when point moves off the screen.  If moving by that number of
>   lines fails to bring point back into view, point is centered instead.
>   The default value is zero, which causes point to always be centered
>   after scrolling.

If you set scroll-conservatively, scroll-step is ignored for the
purposes of deciding how much to scroll when point is off the window.
So the code works as intended.  The documentation is not wrong, as it
describes scroll-conservatively before scroll-step, and the
description quite naturally should lead one to the above conclusion,
because these two variables contradict each other.  I will make the
documentation more clear on this, though.