Make internal links in Org files search for an exact headline match

* lisp/org.el (org-link-search-must-match-exact-headline): New option.
(org-link-search-inhibit-query): New variable.
(org-link-search): Search for exact headline match in Org files
* doc/org.texi (Internal links): Document the changes in internal links.

Internal links used to do a fuzzy text search for the link text.  This
patch changes the behavior for Org files.  Here a link [[My Target]]
now searches for an exact headline match, i.e. for a headline that
does look like "* My Target", optionally with TODO keyword, priority
cookie and tags.

The new option `org-link-search-must-match-exact-headline' is
`query-to-create' by default.  This means that a failed link search
will offer to create the headline as a top-level headline at the end
of the buffer.  This corresponds to a wiki-like behavior where missing
targets are automatically created.  If you do not like this behavior,
change the option to t.

doc/org.texi

@@ -2806,23 +2806,13 @@ text before the first headline is usually not exported, so the first such
 target should be after the first headline, or in the line directly before the
 first headline.}.
 
-If no dedicated target exists, Org will search for the words in the link.  In
-the above example the search would be for @samp{my target}.  Links starting
-with a star like @samp{*My Target} restrict the search to
-headlines@footnote{To insert a link targeting a headline, in-buffer
-completion can be used.  Just type a star followed by a few optional letters
-into the buffer and press @kbd{M-@key{TAB}}.  All headlines in the current
-buffer will be offered as completions.  @xref{Handling links}, for more
-commands creating links.}.  When searching, Org-mode will first try an
-exact match, but then move on to more and more lenient searches.  For
-example, the link @samp{[[*My Targets]]} will find any of the following:
-
-@example
-** My targets
-** TODO my targets are bright
-** my 20 targets are
-@end example
-
+If no dedicated target exists, Org will search for a headline that is exactly
+the link text but may also include a TODO keyword and tags@footnote{To insert
+a link targeting a headline, in-buffer completion can be used.  Just type a
+star followed by a few optional letters into the buffer and press
+@kbd{M-@key{TAB}}.  All headlines in the current buffer will be offered as
+completions.}.  In non-Org files, the search will look for the words in the
+link text, in the above example the search would be for @samp{my target}.
 
 Following a link pushes a mark onto Org's own mark ring.  You can
 return to the previous position with @kbd{C-c &}.  Using this command

lisp/org-exp.el

@@ -1289,18 +1289,19 @@ the current file."
 		   (string-match "^\\." link))
 	       nil)
 	      (t
-	       (save-excursion
-		 (setq found (condition-case nil (org-link-search link)
-			       (error nil)))
-		 (when (and found
-			    (or (org-on-heading-p)
-				(not (eq found 'dedicated))))
-		   (or (get-text-property (point) 'target)
-		       (get-text-property
-			(max (point-min)
-			     (1- (or (previous-single-property-change
-				      (point) 'target) 0)))
-			'target))))))))
+	       (let ((org-link-search-inhibit-query t))
+		 (save-excursion
+		   (setq found (condition-case nil (org-link-search link)
+				 (error nil)))
+		   (when (and found
+			      (or (org-on-heading-p)
+				  (not (eq found 'dedicated))))
+		     (or (get-text-property (point) 'target)
+			 (get-text-property
+			  (max (point-min)
+			       (1- (or (previous-single-property-change
+					(point) 'target) 0)))
+			  'target)))))))))
        (when target
 	 (set-match-data md)
 	 (goto-char (match-beginning 1))

lisp/org.el

@@ -1439,6 +1439,17 @@ Changing this requires a restart of Emacs to work correctly."
   :group 'org-link-follow
   :type 'integer)
 
+(defcustom org-link-search-must-match-exact-headline 'query-to-create
+  "Non-nil means internal links in Org files must exactly match a headline.
+When nil, the link search tries to match a phrase will all words
+in the search text."
+  :group 'org-link-follow
+  :type '(choice
+	  (const :tag "Use fuzy text search" nil)
+	  (const :tag "Match only exact headline" t)
+	  (const :tag "Match extact headline or query to create it"
+		 query-to-create)))
+
 (defcustom org-link-frame-setup
   '((vm . vm-visit-folder-other-frame)
     (gnus . org-gnus-no-new-news)
@@ -9300,6 +9311,7 @@ the window configuration before `org-open-at-point' was called using:
 
     (set-window-configuration org-window-config-before-follow-link)")
 
+(defvar org-link-search-inhibit-query nil) ;; dynamically scoped
 (defun org-link-search (s &optional type avoid-pos)
   "Search for a link search option.
 If S is surrounded by forward slashes, it is interpreted as a
@@ -9317,7 +9329,7 @@ in all files.  If AVOID-POS is given, ignore matches near that position."
 	(pre nil) (post nil)
 	words re0 re1 re2 re3 re4_ re4 re5 re2a re2a_ reall)
     (cond
-     ;; First check if there are any special
+     ;; First check if there are any special search functions
      ((run-hook-with-args-until-success 'org-execute-file-search-functions s))
      ;; Now try the builtin stuff
      ((and (equal (string-to-char s0) ?#)
@@ -9362,8 +9374,28 @@ in all files.  If AVOID-POS is given, ignore matches near that position."
        ;;((eq major-mode 'dired-mode)
        ;; (grep (concat "grep -n -e '" (match-string 1 s) "' *")))
        (t (org-do-occur (match-string 1 s)))))
+     ((and (org-mode-p) org-link-search-must-match-exact-headline)
+      (and (equal (string-to-char s) ?*) (setq s (substring s 1)))
+      (goto-char (point-min))
+      (cond
+       ((let (case-fold-search)
+	  (re-search-forward (format org-complex-heading-regexp-format
+				     (regexp-quote s))
+			     nil t))
+	;; OK, found a match
+	(goto-char (match-beginning 0)))
+       ((and (not org-link-search-inhibit-query)
+	     (eq org-link-search-must-match-exact-headline 'query-to-create)
+	     (y-or-n-p "No match - create this as a new heading? "))
+	(goto-char (point-max))
+	(or (bolp) (newline))
+	(insert "* " s "\n")
+	(beginning-of-line 0))
+       (t
+	(goto-char pos)
+	(error "No match"))))
      (t
-      ;; A normal search strings
+      ;; A normal search string
       (when (equal (string-to-char s) ?*)
 	;; Anchor on headlines, post may include tags.
 	(setq pre "^\\*+[ \t]+\\(?:\\sw+\\)?[ \t]*"
@@ -9408,13 +9440,7 @@ in all files.  If AVOID-POS is given, ignore matches near that position."
 		  )
 	      (goto-char (match-beginning 1))
 	    (goto-char pos)
-	    (error "No match")))))
-     (t
-      ;; Normal string-search
-      (goto-char (point-min))
-      (if (search-forward s nil t)
-	  (goto-char (match-beginning 0))
-	(error "No match"))))
+	    (error "No match"))))))
     (and (org-mode-p) (org-show-context 'link-search))
     type))