org-src.el (org-edit-src-code): Check if we are in a source code block with `org-in-src-block-p'.

* org-src.el (org-edit-src-code): Check if we are in a source
code block with `org-in-src-block-p'.  Slightly reformat the
docstring.

lisp/org-src.el

@@ -201,41 +201,39 @@ There is a mode hook, and keybindings for `org-edit-src-exit' and
 `org-edit-src-save'")
 
 (defun org-edit-src-code (&optional context code edit-buffer-name)
-  "Edit the source CODE example at point.
-The example is copied to a separate buffer, and that buffer is
-switched to the correct language mode.  When done, exit with
-\\[org-edit-src-exit].  This will remove the original code in the
-Org buffer, and replace it with the edited version.  An optional
-argument CONTEXT is used by \\[org-edit-src-save] when calling
-this function.  See `org-src-window-setup' to configure the
-display of windows containing the Org buffer and the code
-buffer."
+  "Edit the source CODE block at point.
+The code is copied to a separate buffer and the appropriate mode
+is turned on.  When done, exit with \\[org-edit-src-exit].  This will
+remove the original code in the Org buffer, and replace it with the
+edited version.  An optional argument CONTEXT is used by \\[org-edit-src-save]
+when calling this function.  See `org-src-window-setup' to configure
+the display of windows containing the Org buffer and the code buffer."
   (interactive)
-  (unless (eq context 'save)
-    (setq org-edit-src-saved-temp-window-config (current-window-configuration)))
-  (let* ((mark (and (org-region-active-p) (mark)))
-	 (case-fold-search t)
-	 (info
-	  ;; If the src region consists in no lines, we insert a blank
-	  ;; line.
-	  (let* ((temp (org-edit-src-find-region-and-lang))
-		 (beg (nth 0 temp))
-		 (end (nth 1 temp)))
-	    (if (>= end beg) temp
-	      (goto-char beg)
-	      (insert "\n")
-	      (org-edit-src-find-region-and-lang))))
-	 (full-info (org-babel-get-src-block-info 'light))
-	 (org-mode-p (derived-mode-p 'org-mode)) ;; derived-mode-p is reflexive
-	 (beg (make-marker))
-	 ;; Move marker with inserted text for case when src block is
-	 ;; just one empty line, i.e. beg == end.
-	 (end (copy-marker (make-marker) t))
-	 (allow-write-back-p (null code))
-	 block-nindent total-nindent ovl lang lang-f single lfmt buffer msg
-	 begline markline markcol line col transmitted-variables)
-    (if (not info)
-	nil
+  (if (not (org-in-src-block-p))
+      (user-error "Not in a source code block")
+    (unless (eq context 'save)
+      (setq org-edit-src-saved-temp-window-config (current-window-configuration)))
+    (let* ((mark (and (org-region-active-p) (mark)))
+	   (case-fold-search t)
+	   (info
+	    ;; If the src region consists in no lines, we insert a blank
+	    ;; line.
+	    (let* ((temp (org-edit-src-find-region-and-lang))
+		   (beg (nth 0 temp))
+		   (end (nth 1 temp)))
+	      (if (>= end beg) temp
+		(goto-char beg)
+		(insert "\n")
+		(org-edit-src-find-region-and-lang))))
+	   (full-info (org-babel-get-src-block-info 'light))
+	   (org-mode-p (derived-mode-p 'org-mode)) ;; derived-mode-p is reflexive
+	   (beg (make-marker))
+	   ;; Move marker with inserted text for case when src block is
+	   ;; just one empty line, i.e. beg == end.
+	   (end (copy-marker (make-marker) t))
+	   (allow-write-back-p (null code))
+	   block-nindent total-nindent ovl lang lang-f single lfmt buffer msg
+	   begline markline markcol line col transmitted-variables)
       (setq beg (move-marker beg (nth 0 info))
 	    end (move-marker end (nth 1 info))
 	    msg (if allow-write-back-p
@@ -244,7 +242,7 @@ buffer."
 		  "Exit with C-c ' (C-c and single quote)")
 	    code (or code (buffer-substring-no-properties beg end))
 	    lang (or (cdr (assoc (nth 2 info) org-src-lang-modes))
-                     (nth 2 info))
+		     (nth 2 info))
 	    lang (if (symbolp lang) (symbol-name lang) lang)
 	    single (nth 3 info)
 	    block-nindent (nth 5 info)