+;;; Default undo-boundary addition
+;;
+;; This section adds a new undo-boundary at either after a command is
+;; called or in some cases on a timer called after a change is made in
+;; any buffer.
+(defvar-local undo-auto--last-boundary-cause nil
+ "Describe the cause of the last undo-boundary.
+
+If `explicit', the last boundary was caused by an explicit call to
+`undo-boundary', that is one not called by the code in this
+section.
+
+If it is equal to `timer', then the last boundary was inserted
+by `undo-auto--boundary-timer'.
+
+If it is equal to `command', then the last boundary was inserted
+automatically after a command, that is by the code defined in
+this section.
+
+If it is equal to a list, then the last boundary was inserted by
+an amalgamating command. The car of the list is the number of
+times an amalgamating command has been called, and the cdr are the
+buffers that were changed during the last command.")
+
+(defvar undo-auto--current-boundary-timer nil
+ "Current timer which will run `undo-auto--boundary-timer' or nil.
+
+If set to non-nil, this will effectively disable the timer.")
+
+(defvar undo-auto--this-command-amalgamating nil
+ "Non-nil if `this-command' should be amalgamated.
+This variable is set to nil by `undo-auto--boundaries' and is set
+by `undo-auto--amalgamate'." )
+
+(defun undo-auto--needs-boundary-p ()
+ "Return non-nil if `buffer-undo-list' needs a boundary at the start."
+ (car-safe buffer-undo-list))
+
+(defun undo-auto--last-boundary-amalgamating-number ()
+ "Return the number of amalgamating last commands or nil.
+Amalgamating commands are, by default, either
+`self-insert-command' and `delete-char', but can be any command
+that calls `undo-auto--amalgamate'."
+ (car-safe undo-auto--last-boundary-cause))
+
+(defun undo-auto--ensure-boundary (cause)
+ "Add an `undo-boundary' to the current buffer if needed.
+REASON describes the reason that the boundary is being added; see
+`undo-auto--last-boundary' for more information."
+ (when (and
+ (undo-auto--needs-boundary-p))
+ (let ((last-amalgamating
+ (undo-auto--last-boundary-amalgamating-number)))
+ (undo-boundary)
+ (setq undo-auto--last-boundary-cause
+ (if (eq 'amalgamate cause)
+ (cons
+ (if last-amalgamating (1+ last-amalgamating) 0)
+ undo-auto--undoably-changed-buffers)
+ cause)))))
+
+(defun undo-auto--boundaries (cause)
+ "Check recently changed buffers and add a boundary if necessary.
+REASON describes the reason that the boundary is being added; see
+`undo-last-boundary' for more information."
+ (dolist (b undo-auto--undoably-changed-buffers)
+ (when (buffer-live-p b)
+ (with-current-buffer b
+ (undo-auto--ensure-boundary cause))))
+ (setq undo-auto--undoably-changed-buffers nil))
+
+(defun undo-auto--boundary-timer ()
+ "Timer which will run `undo--auto-boundary-timer'."
+ (setq undo-auto--current-boundary-timer nil)
+ (undo-auto--boundaries 'timer))
+
+(defun undo-auto--boundary-ensure-timer ()
+ "Ensure that the `undo-auto-boundary-timer' is set."
+ (unless undo-auto--current-boundary-timer
+ (setq undo-auto--current-boundary-timer
+ (run-at-time 10 nil #'undo-auto--boundary-timer))))
+
+(defvar undo-auto--undoably-changed-buffers nil
+ "List of buffers that have changed recently.
+
+This list is maintained by `undo-auto--undoable-change' and
+`undo-auto--boundaries' and can be affected by changes to their
+default values.
+
+See also `undo-auto--buffer-undoably-changed'.")
+
+(defun undo-auto--add-boundary ()
+ "Add an `undo-boundary' in appropriate buffers."
+ (undo-auto--boundaries
+ (if undo-auto--this-command-amalgamating
+ 'amalgamate
+ 'command))
+ (setq undo-auto--this-command-amalgamating nil))
+
+(defun undo-auto--amalgamate ()
+ "Amalgamate undo if necessary.
+This function can be called after an amalgamating command. It
+removes the previous `undo-boundary' if a series of such calls
+have been made. By default `self-insert-command' and
+`delete-char' are the only amalgamating commands, although this
+function could be called by any command wishing to have this
+behaviour."
+ (let ((last-amalgamating-count
+ (undo-auto--last-boundary-amalgamating-number)))
+ (setq undo-auto--this-command-amalgamating t)
+ (when
+ last-amalgamating-count
+ (if
+ (and
+ (< last-amalgamating-count 20)
+ (eq this-command last-command))
+ ;; Amalgamate all buffers that have changed.
+ (dolist (b (cdr undo-auto--last-boundary-cause))
+ (when (buffer-live-p b)
+ (with-current-buffer
+ b
+ (when
+ ;; The head of `buffer-undo-list' is nil.
+ ;; `car-safe' doesn't work because
+ ;; `buffer-undo-list' need not be a list!
+ (and (listp buffer-undo-list)
+ (not (car buffer-undo-list)))
+ (setq buffer-undo-list
+ (cdr buffer-undo-list))))))
+ (setq undo-auto--last-boundary-cause 0)))))
+
+(defun undo-auto--undoable-change ()
+ "Called after every undoable buffer change."
+ (add-to-list 'undo-auto--undoably-changed-buffers (current-buffer))
+ (undo-auto--boundary-ensure-timer))
+;; End auto-boundary section
+