Allow time stampes without day name

* lisp/org-clock.el (org-clock-in):
(org-clock-find-position): Make space after date optional.
* lisp/org.el (org-set-regexps-and-options):
(org-ts-regexp):
(org-ts-regexp-both):
(org-ts-regexp1):
(org-ctrl-c-ctrl-c): Make `C-c C-c' on date fix the time stamp

* doc/org.texi (Creating timestamps): Document the effect of `C-c C-c'
on a timestamp.

doc/org.texi

@@ -5267,13 +5267,15 @@ is used in a much wider sense.
 @cindex scheduling
 
 A timestamp is a specification of a date (possibly with a time or a range of
-times) in a special format, either @samp{<2003-09-16 Tue>} or
-@samp{<2003-09-16 Tue 09:39>} or @samp{<2003-09-16 Tue
-12:00-12:30>}@footnote{This is inspired by the standard ISO 8601 date/time
-format.  To use an alternative format, see @ref{Custom time format}.}.  A
-timestamp can appear anywhere in the headline or body of an Org tree entry.
-Its presence causes entries to be shown on specific dates in the agenda
-(@pxref{Weekly/daily agenda}).  We distinguish:
+times) in a special format, either @samp{<2003-09-16 Tue>}@footnote{In this
+simplest form, the day name is optional when you type the date yourself.
+However, any dates inserted or modified by Org will add that day name, for
+reading convenience.} or @samp{<2003-09-16 Tue 09:39>} or @samp{<2003-09-16
+Tue 12:00-12:30>}@footnote{This is inspired by the standard ISO 8601
+date/time format.  To use an alternative format, see @ref{Custom time
+format}.}.  A timestamp can appear anywhere in the headline or body of an Org
+tree entry.  Its presence causes entries to be shown on specific dates in the
+agenda (@pxref{Weekly/daily agenda}).  We distinguish:
 
 @table @var
 @item Plain timestamp; Event; Appointment
@@ -5374,6 +5376,9 @@ Like @kbd{C-c .} and @kbd{C-c !}, but use the alternative format which
 contains date and time.  The default time can be rounded to multiples of 5
 minutes, see the option @code{org-time-stamp-rounding-minutes}.
 @c
+@orgkey{C-c C-c}
+Normalize timestamp, insert/fix day name if missing or wrong.
+@c
 @orgcmd{C-c <,org-date-from-calendar}
 Insert a timestamp corresponding to the cursor date in the Calendar.
 @c
@@ -13770,6 +13775,8 @@ ordered list.
 @item
 If the cursor is on the @code{#+BEGIN} line of a dynamic block, the
 block is updated.
+@item
+If the cursor is at a timestamp, fix the day name in the timestamp.
 @end itemize
 
 @node Clean view, TTY keys, The very busy C-c C-c key, Miscellaneous

lisp/org-clock.el

@@ -1117,7 +1117,7 @@ the clocking selection, associated with the letter `d'."
 		   (looking-at
 		    (concat "^[ \t]* " org-clock-string
 			    " \\[\\([0-9]\\{4\\}-[0-9]\\{2\\}-[0-9]\\{2\\}"
-			    " +\\sw+\.? +[012][0-9]:[0-5][0-9]\\)\\][ \t]*$")))
+			    " *\\sw+\.? +[012][0-9]:[0-5][0-9]\\)\\][ \t]*$")))
 	      (message "Matched %s" (match-string 1))
 	      (setq ts (concat "[" (match-string 1) "]"))
 	      (goto-char (match-end 1))
@@ -1249,7 +1249,7 @@ line and position cursor in that line."
 		 (re-search-forward
 		  (concat "^[ \t]* " org-clock-string
 			  " \\[\\([0-9]\\{4\\}-[0-9]\\{2\\}-[0-9]\\{2\\}"
-			  " +\\sw+ +[012][0-9]:[0-5][0-9]\\)\\][ \t]*$")
+			  " *\\sw+ +[012][0-9]:[0-5][0-9]\\)\\][ \t]*$")
 		  end t))
 	(beginning-of-line 1)
 	(throw 'exit t))

lisp/org.el

@@ -4724,7 +4724,7 @@ means to push this value onto the list in the variable.")
 		    "\\|" org-deadline-string
 		    "\\|" org-closed-string
 		    "\\|" org-clock-string "\\)\\)?"
-		    " *\\([[<][0-9]\\{4\\}-[0-9]\\{2\\}-[0-9]\\{2\\} [^]\r\n>]*?[]>]\\|<%%([^\r\n>]*>\\)")
+		    " *\\([[<][0-9]\\{4\\}-[0-9]\\{2\\}-[0-9]\\{2\\} ?[^]\r\n>]*?[]>]\\|<%%([^\r\n>]*>\\)")
 	    org-planning-or-clock-line-re
 	    (concat "\\(?:^[ \t]*\\(" org-scheduled-string
 		    "\\|" org-deadline-string
@@ -5189,15 +5189,15 @@ This should be called after the variable `org-link-types' has changed."
 
 (org-make-link-regexps)
 
-(defconst org-ts-regexp "<\\([0-9]\\{4\\}-[0-9]\\{2\\}-[0-9]\\{2\\} [^\r\n>]*?\\)>"
+(defconst org-ts-regexp "<\\([0-9]\\{4\\}-[0-9]\\{2\\}-[0-9]\\{2\\} ?[^\r\n>]*?\\)>"
   "Regular expression for fast time stamp matching.")
-(defconst org-ts-regexp-both "[[<]\\([0-9]\\{4\\}-[0-9]\\{2\\}-[0-9]\\{2\\} [^]\r\n>]*?\\)[]>]"
+(defconst org-ts-regexp-both "[[<]\\([0-9]\\{4\\}-[0-9]\\{2\\}-[0-9]\\{2\\} ?[^]\r\n>]*?\\)[]>]"
   "Regular expression for fast time stamp matching.")
 (defconst org-ts-regexp0 "\\(\\([0-9]\\{4\\}\\)-\\([0-9]\\{2\\}\\)-\\([0-9]\\{2\\}\\) *\\([^]+0-9>\r\n -]*\\)\\( \\([0-9]\\{2\\}\\):\\([0-9]\\{2\\}\\)\\)?\\)"
   "Regular expression matching time strings for analysis.
 This one does not require the space after the date, so it can be used
 on a string that terminates immediately after the date.")
-(defconst org-ts-regexp1 "\\(\\([0-9]\\{4\\}\\)-\\([0-9]\\{2\\}\\)-\\([0-9]\\{2\\}\\) +\\([^]+0-9>\r\n -]*\\)\\( \\([0-9]\\{2\\}\\):\\([0-9]\\{2\\}\\)\\)?\\)"
+(defconst org-ts-regexp1 "\\(\\([0-9]\\{4\\}\\)-\\([0-9]\\{2\\}\\)-\\([0-9]\\{2\\}\\) *\\([^]+0-9>\r\n -]*\\)\\( \\([0-9]\\{2\\}\\):\\([0-9]\\{2\\}\\)\\)?\\)"
   "Regular expression matching time strings for analysis.")
 (defconst org-ts-regexp2 (concat "<" org-ts-regexp1 "[^>\n]\\{0,16\\}>")
   "Regular expression matching time stamps, with groups.")
@@ -18236,6 +18236,8 @@ This command does many different things, depending on context:
 	   (fboundp org-finish-function))
       (funcall org-finish-function))
      ((run-hook-with-args-until-success 'org-ctrl-c-ctrl-c-hook))
+     ((org-in-regexp org-ts-regexp-both)
+      (org-timestamp-change 0 'day))
      ((or (looking-at org-property-start-re)
 	  (org-at-property-p))
       (call-interactively 'org-property-action))