Footnotes: Automatic label creation.

This patch implements fully automatic creation of unique labels for
footnotes, which is also turned on as the default setting.  The
automatic labels look like [fn:1], [fn:2], etc, using the first
available unused number.

The commit introduces a new variable, `org-footnote-auto-label' with a
number of different options ranging from no auto creation (prompting
the user for a label) to fully automatic creation.

Also, the commit introduces new #+STARTUP options that can be used to
select these settings on a per-file basis.

ORGWEBPAGE/Changes.org

@@ -31,14 +31,17 @@ For example:
  [1] The link is: http://orgmode.org
 #+end_src
 
-   Org-mode extends the number-based syntax to _named_ footnotes and
-optional inline definition.  Using numbers as markers is supported for
-backward compatibility.  Here are the valid references:
+Org-mode extends the number-based syntax to /named/ footnotes and
+optional inline definition.  Using numbers as markers is
+supported for backward compatibility, but not encouraged because
+of possible conflicts with LaTeX syntax.  Here are the valid
+references:
 
-- [1] ::  A numeric footnote marker.
+- [1] ::  A plain numeric footnote marker.
 	 
 - [fn:name] :: A named footnote reference, where `name' is a
-     unique label word. 
+     unique label word or, for simplicity of automatic creation,
+     a number. 
      
 - [fn:: This is the inline definition of this footnote] ::
      A LaTeX-like anonymous footnote where the definition is given
@@ -50,17 +53,23 @@ backward compatibility.  Here are the valid references:
      note, you can then use use `[fn:name]' to create additional
      references.
 
+Footnote labels can be created automatically, or you create names
+yourself.  This is handled by the variable
+=org-footnote-auto-label= and its corresponding =#+STARTUP=
+keywords, see the docstring of that variable for details.
+
 The following command handles footnotes:
 
 - C-c C-x f ::
-     The footnote action command.  When the cursor is on a footnote
-     reference, jump to the definition.  When it is at a definition,
-     jump to the (first) reference.  Otherwise, create a new footnote.
-     Depending on the variable `org-footnote-define-inline' (with
-     associated #+STARTUP options fninline and nofninline), the
-     definitions will be placed locally, or into the nearest outline
-     section with the heading `Footnotes'.  If no such section is found
-     after the reference point, one will be created at the end of the
+     The footnote action command.  When the cursor is on a
+     footnote reference, jump to the definition.  When it is at a
+     definition, jump to the (first) reference.  Otherwise,
+     create a new footnote.  Depending on the variable
+     `org-footnote-define-inline' (with associated =#+STARTUP=
+     options =fninline= and =nofninline=), the definitions will
+     be placed locally, or into the nearest outline section with
+     the heading `Footnotes'.  If no such section is found after
+     the reference point, one will be created at the end of the
      file.
      When this command is called with a prefix argument, a menu of
      additional options is offered:

doc/org.texi

@@ -1379,20 +1379,23 @@ brackets in column 0, no indentation allowed.  The footnote reference is
 simply the marker in square brackets, inside text.  For example:
 
 @example
-The Org homepage[1] now looks a lot better than it used to.
+The Org homepage[fn:1] now looks a lot better than it used to.
 ...
-[1] The link is: http://orgmode.org
+[fn:1] The link is: http://orgmode.org
 @end example
 
 Org-mode extends the number-based syntax to @emph{named} footnotes and
-optional inline definition.  Using numbers as markers is supported for
-backward compatibility.  Here are the valid references:
+optional inline definition.  Using plain numbers as markers (as
+@file{footnote.el} does) is supported for backward compatibility, but not
+encouraged because of possible conflicts with LaTeX snippets @pxref{Embedded
+LaTeX}.  Here are the valid references:
 
 @table @code
 @item [1]
-A numeric footnote marker.
+A plain numeric footnote marker.
 @item [fn:name]
-A named footnote reference, where @code{name} is a unique label word.
+A named footnote reference, where @code{name} is a unique label word, or, for
+simplicity of automatic creation, a number.
 @item [fn:: This is the inline definition of this footnote]
 A LaTeX-like anonymous footnote where the definition is given directly at the
 reference point.
@@ -1402,6 +1405,11 @@ Since Org allows multiple references to the same note, you can then use use
 @code{[fn:name]} to create additional references.
 @end table
 
+Footnote labels can be created automatically, or you create names yourself.
+This is handled by the variable @code{org-footnote-auto-label} and its
+corresponding @code{#+STARTUP} keywords, see the docstring of that variable
+for details.
+
 @noindent The following command handles footnotes:
 
 @table @kbd
@@ -8819,6 +8827,23 @@ The following options influence the table spreadsheet (variable
 constcgs   @r{@file{constants.el} should use the c-g-s unit system}
 constSI    @r{@file{constants.el} should use the SI unit system}
 @end example
+To influence footnote settings, use the following keywords.  The
+corresponding variables are @code{org-footnote-define-inline} and
+@code{org-footnote-auto-label}.
+@cindex @code{fninline}, STARTUP keyword
+@cindex @code{fnnoinline}, STARTUP keyword
+@cindex @code{fnprompt}, STARTUP keyword
+@cindex @code{fnauto}, STARTUP keyword
+@cindex @code{fnconfirm}, STARTUP keyword
+@cindex @code{fnplain}, STARTUP keyword
+@example
+fninline    @r{define footnotes inline}
+fnnoinline  @r{define footnotes in separate section}
+fnprompt    @r{prompt for footnote labels}
+fnauto      @r{create [fn:1]-like labels automatically (default)}
+fnconfirm   @r{offer automatic label for editing or confirmation}
+fnplain     @r{create [1]-like labels automatically}
+@end example
 @item #+TAGS:  TAG1(c1) TAG2(c2)
 These lines (several such lines are allowed) specify the valid tags in
 this file, and (potentially) the corresponding @emph{fast tag selection}

lisp/org-footnote.el

@@ -92,6 +92,23 @@ will be used to define the footnote at the reference position."
   :group 'org-footnote
   :type 'boolean)
 
+(defcustom org-footnote-auto-label t
+  "Non-nil means, define automatically new labels for footnotes.
+Possible values are:
+
+nil        prompt the user for each label
+t          create unique labels of the form [fn:1], [fn:2], ...
+confirm    like t, but let the user edit the created value.  In particular,
+           the label can be removed from the minibuffer, to create
+           an anonymous footnote.
+plain      Automatically create plain number labels like [1]"
+  :group 'org-footnote
+  :type '(choice
+	  (const :tag "Frompt for label" nil)
+	  (const :tag "Create automatic [fn:N]" t)
+	  (const :tag "Offer automatic [fn:N] for editing" confirm)
+	  (const :tag "Create automatic [N]" plain)))
+
 (defun org-footnote-at-reference-p ()
   "Is the cursor at a footnote reference?
 If yes, return the beginning position, the label, and the definition, if local."
@@ -175,6 +192,20 @@ with start and label of the footnote if there is a definition at point."
 	  (and l (not (equal l "fn:")) (add-to-list 'rtn l)))))
     rtn))
 
+(defun org-footnote-unique-label (&optional current)
+  "Return a new unique footnote label.
+The returns the firsts fn:N labels that is currently not used."
+  (unless current (setq current (org-footnote-all-labels)))
+  (let ((fmt (if (eq org-footnote-auto-label 'plain) "%d" "fn:%d"))
+	(cnt 1))
+    (while (member (format fmt cnt) current)
+      (incf cnt))
+    (format fmt cnt)))
+
+(defvar org-footnote-label-history nil
+  "History of footnote labels entered in current buffer.")
+(make-variable-buffer-local 'org-footnote-label-history)
+
 (defun org-footnote-new ()
   "Insert a new footnote.
 This command prompts for a label.  If this is a label referencing an
@@ -182,9 +213,15 @@ existing label, only insert the label.  If the footnote label is empty
 or new, let the user edit the definition of the footnote."
   (interactive)
   (let* ((labels (org-footnote-all-labels))
-	 (label (completing-read
-		 "Label (leave empty for anonymous): "
-		 (mapcar 'list labels))))
+	 (propose (org-footnote-unique-label labels))
+	 (label
+	  (if (member org-footnote-auto-label '(t plain))
+	      propose
+	    (completing-read
+	     "Label (leave empty for anonymous): "
+	     (mapcar 'list labels) nil nil
+	     (if (eq org-footnote-auto-label 'confirm) propose nil)
+	     'org-footnote-label-history))))
     (setq label (org-footnote-normalize-label label))
     (cond
      ((equal label "")

lisp/org.el

@@ -2995,6 +2995,10 @@ After a match, the following groups carry important information:
     ("nologrepeat" org-log-repeat nil)
     ("fninline" org-footnote-define-inline t)
     ("nofninline" org-footnote-define-inline nil)
+    ("fnauto" org-footnote-auto-label t)
+    ("fnprompt" org-footnote-auto-label nil)
+    ("fnconfirm" org-footnote-auto-label confirm)
+    ("fnplain" org-footnote-auto-label plain)
     ("constcgs" constants-unit-system cgs)
     ("constSI" constants-unit-system SI))
   "Variable associated with STARTUP options for org-mode.