bug#15744: ansi-term: prompt moves to bottom of screen

[Ryan Crum]

Hi,

Here's a patch that adds a variable `term-scroll-snap-to-bottom` in an attempt 
resolve this. It defaults to t to preserve current behavior (arguably best for 
curses-type interactions), but when you set it to nil it keeps your current 
scrolling position while typing as long as the prompt is still visible in the 
window.

It also works with `term-scroll-show-maximum-output` to handle cases where 
output is printed below the prompt (ala zsh).

This patch is against trunk.

-Ryan



*** term.el.orig        Mon Oct 28 21:53:50 2013
--- term.el     Mon Oct 28 21:53:05 2013
*************** This variable is buffer-local."
*** 551,556 ****
--- 551,564 ----
    :type 'boolean
    :group 'term)
  
+ (defcustom term-scroll-snap-to-bottom t
+   "If t, when the prompt is visible within the buffer then scroll
+ so that the prompt is on the bottom on any input or output.
+ 
+ The default is t."
+   :type 'boolean
+   :group 'term)
+ 
  (defcustom term-scroll-show-maximum-output nil
    "Controls how interpreter output causes window to scroll.
  If non-nil, then show the maximum output when the window is scrolled.
*************** See `term-prompt-regexp'."
*** 3114,3128 ****
                                    (or (eq scroll 'this) (not save-point)))
                               (and (eq scroll 'others)
                                    (not (eq selected win))))
!                      (goto-char term-home-marker)
!                      (recenter 0)
                       (goto-char (process-mark proc))
                       (if (not (pos-visible-in-window-p (point) win))
                           (recenter -1)))
                     ;; Optionally scroll so that the text
                     ;; ends at the bottom of the window.
                     (when (and term-scroll-show-maximum-output
!                               (>= (point) (process-mark proc)))
                       (save-excursion
                         (goto-char (point-max))
                         (recenter -1)))))
--- 3122,3139 ----
                                    (or (eq scroll 'this) (not save-point)))
                               (and (eq scroll 'others)
                                    (not (eq selected win))))
!                      (when term-scroll-snap-to-bottom
!                        (goto-char term-home-marker)
!                        (recenter 0))
                       (goto-char (process-mark proc))
                       (if (not (pos-visible-in-window-p (point) win))
                           (recenter -1)))
                     ;; Optionally scroll so that the text
                     ;; ends at the bottom of the window.
                     (when (and term-scroll-show-maximum-output
!                               (>= (point) (process-mark proc))
!                               (or term-scroll-snap-to-bottom
!                                   (not (pos-visible-in-window-p (point-max) 
win))))
                       (save-excursion
                         (goto-char (point-max))
                         (recenter -1)))))