Better support for the case of typing RET on the prompt in comint.

* lisp/comint.el (comint-get-old-input-default): Go to the field end
when comint-use-prompt-regexp is nil.
(comint-line-beginning-position): Check if point is already
on the prompt before searching for the prompt when
comint-use-prompt-regexp is non-nil.

Fixes: debbugs:19710

lisp/ChangeLog

@@ -1,3 +1,13 @@
+2015-02-10  Juri Linkov  <juri@linkov.net>
+
+	Better support for the case of typing RET on the prompt in comint.
+
+	* comint.el (comint-get-old-input-default): Go to the field end
+	when comint-use-prompt-regexp is nil.
+	(comint-line-beginning-position): Check if point is already
+	on the prompt before searching for the prompt when
+	comint-use-prompt-regexp is non-nil.  (Bug#19710)
+
 2015-02-08  Eli Zaretskii  <eliz@gnu.org>
 
 	* frame.el (frame-notice-user-settings): Refresh the value of

lisp/comint.el

@@ -2215,7 +2215,10 @@ the current line with any initial string matching the regexp
              (null (get-char-property (setq bof (field-beginning)) 'field)))
 	(field-string-no-properties bof)
       (comint-bol)
-      (buffer-substring-no-properties (point) (line-end-position)))))
+      (buffer-substring-no-properties (point)
+				      (if comint-use-prompt-regexp
+					  (line-end-position)
+					(field-end))))))
 
 (defun comint-copy-old-input ()
   "Insert after prompt old input at point as new input to be edited.
@@ -2263,8 +2266,9 @@ a buffer local variable."
   (if comint-use-prompt-regexp
       ;; Use comint-prompt-regexp
       (save-excursion
-	(re-search-backward comint-prompt-regexp nil t)
 	(beginning-of-line)
+	(unless (looking-at comint-prompt-regexp)
+	  (re-search-backward comint-prompt-regexp nil t))
 	(comint-skip-prompt)
 	(point))
     ;; Use input fields.  Note that, unlike the behavior of