bug#12253: Restore window start position

[Juri Linkov]

> I agree.  How do you handle the case where *info* is not in the selected
> window but some other one?

We don't need to care about this case.  When used programmatically,
the caller should handle also the case when *info* is in another window,
e.g.:

  (with-current-buffer "*info*"
    ...
    (Info-history-back)
    (set-window-start (window-in-direction 'below) opoint)
    ...)

or some more specific logic when necessary.

But for the normal case, I think the following patch should be enough:

=== modified file 'lisp/info.el'
--- lisp/info.el        2012-08-21 00:12:42 +0000
+++ lisp/info.el        2012-08-25 19:29:04 +0000
@@ -40,11 +40,11 @@ (defgroup info nil
 
 (defvar Info-history nil
   "Stack of Info nodes user has visited.
-Each element of the stack is a list (FILENAME NODENAME BUFFERPOS).")
+Each element of the stack is a list (FILENAME NODENAME BUFFERPOS WINDOWPOS).")
 
 (defvar Info-history-forward nil
   "Stack of Info nodes user has visited with `Info-history-back' command.
-Each element of the stack is a list (FILENAME NODENAME BUFFERPOS).")
+Each element of the stack is a list (FILENAME NODENAME BUFFERPOS WINDOWPOS).")
 
 (defvar Info-history-list nil
   "List of all Info nodes user has visited.
@@ -922,7 +925,9 @@ (defun Info-find-node (filename nodename
   ;; Record the node we are leaving, if we were in one.
   (and (not no-going-back)
        Info-current-file
-       (push (list Info-current-file Info-current-node (point))
+       (push (list Info-current-file Info-current-node (point)
+                  (and (eq (window-buffer) (current-buffer))
+                       (window-start)))
              Info-history))
   (Info-find-node-2 filename nodename no-going-back))
 
@@ -956,7 +961,9 @@ (defun Info-revert-find-node (filename n
        (pline        (count-lines (point-min) (line-beginning-position)))
        (wline        (count-lines (point-min) (window-start)))
        (new-history  (and Info-current-file
-                          (list Info-current-file Info-current-node (point)))))
+                          (list Info-current-file Info-current-node (point)
+                                (and (eq (window-buffer) (current-buffer))
+                                     (window-start))))))
     ;; When `Info-current-file' is nil, `Info-find-node-2' rereads the file.
     (setq Info-current-file nil)
     (Info-find-node filename nodename)
@@ -1226,6 +1233,8 @@ (defun Info-find-node-2 (filename nodena
         (let ((hist (car Info-history)))
           (setq Info-history (cdr Info-history))
           (Info-find-node (nth 0 hist) (nth 1 hist) t)
+          (when (and (nth 3 hist) (eq (window-buffer) (current-buffer)))
+           (set-window-start (selected-window) (nth 3 hist) t))
           (goto-char (nth 2 hist))))))
 
 ;; Cache the contents of the (virtual) dir file, once we have merged
@@ -2002,7 +2013,7 @@ (defun Info-search (regexp &optional bou
               (equal ofile Info-current-file))
           (and isearch-mode isearch-wrapped
               (eq opoint (if isearch-forward opoint-min opoint-max)))
-         (setq Info-history (cons (list ofile onode opoint)
+         (setq Info-history (cons (list ofile onode opoint ostart)
                                   Info-history))))))
 
 (defun Info-search-case-sensitively ()
@@ -2208,16 +2219,21 @@ (defun Info-history-back ()
   (or Info-history
       (user-error "This is the first Info node you looked at"))
   (let ((history-forward
-        (cons (list Info-current-file Info-current-node (point))
+        (cons (list Info-current-file Info-current-node (point)
+                    (and (eq (window-buffer) (current-buffer))
+                         (window-start)))
               Info-history-forward))
-       filename nodename opoint)
+       filename nodename opoint ostart)
     (setq filename (car (car Info-history)))
     (setq nodename (car (cdr (car Info-history))))
     (setq opoint (car (cdr (cdr (car Info-history)))))
+    (setq ostart (car (cdr (cdr (cdr (car Info-history))))))
     (setq Info-history (cdr Info-history))
     (Info-find-node filename nodename)
     (setq Info-history (cdr Info-history))
     (setq Info-history-forward history-forward)
+    (when (and ostart (eq (window-buffer) (current-buffer)))
+      (set-window-start (selected-window) ostart t))
     (goto-char opoint)))
 
 (defalias 'Info-last 'Info-history-back)
@@ -2228,12 +2244,15 @@ (defun Info-history-forward ()
   (or Info-history-forward
       (user-error "This is the last Info node you looked at"))
   (let ((history-forward (cdr Info-history-forward))
-       filename nodename opoint)
+       filename nodename opoint ostart)
     (setq filename (car (car Info-history-forward)))
     (setq nodename (car (cdr (car Info-history-forward))))
     (setq opoint (car (cdr (cdr (car Info-history-forward)))))
+    (setq ostart (car (cdr (cdr (cdr (car Info-history-forward))))))
     (Info-find-node filename nodename)
     (setq Info-history-forward history-forward)
+    (when (and ostart (eq (window-buffer) (current-buffer)))
+      (set-window-start (selected-window) ostart t))
     (goto-char opoint)))
 
 (add-to-list 'Info-virtual-files
@@ -4307,7 +4326,7 @@ (defun Info-find-emacs-command-nodes (co
              (setq where
                    (cons (list Info-current-file
                                (match-string-no-properties 2)
-                               0)
+                               0 0)
                          where))
              (setq line-number (and (match-beginning 3)
                                     (string-to-number (match-string 3)))))