bug#17787: 24.4.50; Making `linum-mode` more efficient -- no need to run multiple times.

[Keith David Bershatsky]

Linum-mode could be made more efficient by including conditions to ensure that 
it only runs one time, instead of 1 to 3 times.  To see exactly what I am 
talking about, a message can be placed immediately following the let-bound 
variables in the function `linum-update-window`

(message "point: %s | limit: %s" (point) limit)

This happens for a few reasons.  The `window-scroll-functions` hook is really 
only needed when point moves outside the visible window limits.  When point is 
greater than the first value of `(window-end win t)` reported by the initial 
run of the `window-scroll-functions` hook, the hook runs a second time -- 
presumably so that redisplay can do its job correctly.  When the 
`window-scroll-functions` hook runs the second time under that scenario, it 
gets it right -- i.e., the second time around the `(window-end win t)` reports 
the correct result.  So there is no point drawing and removing overlays the 
first time around when it has the wrong `(window-end win t)`.

In addition, the `post-command-hook` function is only needed when point stays 
within the visible limit limits.

Here is a minor mode that can be used to test the `window-start` and 
`window-end` values.  A similar system can be used for `linum-mode` -- i.e., 
use the `linum-update-window` from the `post-command-hook` when point stays 
within the visible window limits; and, when point moves outside those visible 
window limits, then use the `window-scroll-functions` hook -- however, limit 
`linum-update-window` so that it only runs when `(not (> (point) (window-end 
win t)))`.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; A minor-mode for testing `window-start` and `window-end` BEFORE visual 
redisplay.

(defvar old-window-start nil
"This local variable is set within the `post-command-hook`; and,
is also used by the `window-scroll-functions` hook.")
(make-variable-buffer-local 'old-window-start)

(defvar old-window-end nil
"This local variable is set within the `post-command-hook`; and,
is also used by the `window-scroll-functions` hook.")
(make-variable-buffer-local 'old-window-end)

(defvar old-window-end-forced nil
"This local variable is set within the `post-command-hook`; and,
is also used by the `window-scroll-functions` hook.")
(make-variable-buffer-local 'old-window-end-forced)

(defvar new-window-start nil
"This local variable is set within the `window-scroll-functions`.")
(make-variable-buffer-local 'new-window-start)

(defvar new-window-end nil
"This local variable is set within the `window-scroll-functions`.")
(make-variable-buffer-local 'new-window-end)

(defun test-post-command-hook ()
"NOT good for things like: `beginning-of-buffer`; `end-of-buffer`; `yank`; etc.
NOTE:  When using `this-command` in conjunction with the `post-command-hook`,
the `window-scroll-functions` hook would need to use `last-command`."
  (when
      (and
        (not (minibufferp))
        (window-live-p (get-buffer-window (current-buffer))))
    (setq old-window-start (window-start))
    (setq old-window-end (window-end))
    (setq old-window-end-forced (window-end nil t))
    (when
        (and
          (not (< (point) old-window-start))
          (not (> (point) old-window-end))
          (not (> (point) old-window-end-forced)))
      (message (concat
        "P.C.H. -- `point`: %s | "
        "`old-window-start`: %s | "
        "`old-window-end`: %s | "
        "`old-window-end-forced`: %s")
          (point)
          old-window-start
          old-window-end
          old-window-end-forced))))

(defun test-window-scroll-functions (win _start)
"Good for things like: `beginning-of-buffer`; `end-of-buffer`; `yank`; etc.
NOTE:  When using `this-command` in conjunction with the `post-command-hook`,
the `window-scroll-functions` hook would need to use `last-command`."
  (when
      (and
        (not (> (point) (window-end win t)))
        old-window-start
        old-window-end
        old-window-end-forced
        (not (minibufferp))
        (window-live-p (get-buffer-window (current-buffer))))
    (when
        (or
          (< (point) old-window-start)
          (> (point) old-window-end)
          (> (point) old-window-end-forced))
      (setq new-window-start _start)
      (setq new-window-end (window-end win t))
      (message (concat
        "W.S.F. -- `point`: %s | "
        "`new-window-start`: %s | "
        "`new-window-end`: %s")
          (point)
          new-window-start
          new-window-end)
        (setq old-window-start nil)
        (setq old-window-end nil)
        (setq old-window-end-forced nil))))

(define-minor-mode test-mode
"A minor-mode for testing `window-start` and `window-end` BEFORE visual 
redisplay."
  :init-value nil
  :lighter " 𝓣𝓔𝓢𝓣"
  :keymap nil
  :global nil
  (cond
    (test-mode
      (condition-case error
        (progn
          (setq scroll-conservatively 101)
          (setq scroll-margin 0)
          (add-hook 'post-command-hook 'test-post-command-hook nil t)
          (add-hook 'window-scroll-functions 'test-window-scroll-functions nil 
t)
          (message "Turned ON `test-mode`."))
        (error
         (test-mode 0)
         (signal (car error) (cdr error)))))
    ((not test-mode)
      (remove-hook 'post-command-hook 'test-post-command-hook t)
      (remove-hook 'window-scroll-functions 'test-window-scroll-functions t)
      (message "Turned OFF `test-mode`.") )))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;


In GNU Emacs 24.4.50.1 (x86_64-apple-darwin10.8.0, NS appkit-1038.36 Version 
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