Backport commit e14c0d748 from Emacs

* lisp/org-datetree.el (org-datetree--find-create):
* lisp/org-pcomplete.el (org-thing-at-point):
Fix regular expression and similar syntax.

More minor regex cleanup
e14c0d748efe35afc653151ff18c4dd93dcc456e
Paul Eggert
Tue Mar 19 18:47:53 2019 -0700

lisp/org-datetree.el

@@ -138,15 +138,16 @@ will be built under the headline at point."
        "^\\*+[ \t]+%d-%02d-\\([0123][0-9]\\) \\w+$"
        year month day))))
 
-(defun org-datetree--find-create (regex year &optional month day insert)
-  "Find the datetree matched by REGEX for YEAR, MONTH, or DAY.
-REGEX is passed to `format' with YEAR, MONTH, and DAY as
+(defun org-datetree--find-create
+    (regex-template year &optional month day insert)
+  "Find the datetree matched by REGEX-TEMPLATE for YEAR, MONTH, or DAY.
+REGEX-TEMPLATE is passed to `format' with YEAR, MONTH, and DAY as
 arguments.  Match group 1 is compared against the specified date
 component.  If INSERT is non-nil and there is no match then it is
 inserted into the buffer."
   (when (or month day)
     (org-narrow-to-subtree))
-  (let ((re (format regex year month day))
+  (let ((re (format regex-template year month day))
 	match)
     (goto-char (point-min))
     (while (and (setq match (re-search-forward re nil t))

lisp/org-pcomplete.el

@@ -93,7 +93,7 @@ The return value is a string naming the thing at point."
       (cons "file-option" nil))
      ;; Link abbreviation.
      ((save-excursion
-	(skip-chars-backward "A-Za-z0-9-_")
+	(skip-chars-backward "-A-Za-z0-9_")
 	(and (eq ?\[ (char-before))
 	     (eq ?\[ (char-before (1- (point))))))
       (cons "link" nil))