* c-mode.el (c-fill-paragraph): Calculating the proper fill-prefix

	shouldn't change the buffer text.  Make it not.  If we're in the
	blank space before another comment, fill that one as a comment,
	not as normal text.

	* c-mode.el (c-fill-paragraph): When guessing the fill prefix,
	don't ever grab any actual text.

1 files changed, 52 insertions, 14 deletions

diff --git a/lisp/progmodes/c-mode.el b/lisp/progmodes/c-mode.el
index aa766148743..56db49bc5c5 100644
--- a/lisp/progmodes/c-mode.el
+++ b/lisp/progmodes/c-mode.el
@@ -244,7 +244,7 @@ preserving the comment indentation or line-starting decorations."
           ;; Check for obvious entry to comment.
           (save-excursion
             (beginning-of-line)
-            (skip-chars-forward " \t")
+            (skip-chars-forward " \t\n")
             (and (looking-at comment-start-skip)
                  (setq comment-start-place (point))))))
     (if (or first-line
@@ -252,13 +252,14 @@ preserving the comment indentation or line-starting decorations."
             (eq (calculate-c-indent) t)
             ;; t if this line contains a comment starter.
             (setq first-line
-                  (save-excursion (beginning-of-line)
-                                  (prog1
-                                      (re-search-forward comment-start-skip
-                                                         (save-excursion (end-of-line)
-                                                                         (point))
-                                                         t)
-                                    (setq comment-start-place (point))))))
+                  (save-excursion
+                    (beginning-of-line)
+                    (prog1
+                        (re-search-forward comment-start-skip
+                                           (save-excursion (end-of-line)
+                                                           (point))
+                                           t)
+                      (setq comment-start-place (point))))))
         ;; Inside a comment: fill one comment paragraph.
         (let ((fill-prefix
                ;; The prefix for each line of this paragraph
@@ -270,12 +271,49 @@ preserving the comment indentation or line-starting decorations."
                      (progn (re-search-forward comment-start-skip)
                             (make-string (current-column) ?\ ))
                    (if first-line (forward-line 1))
-                   (buffer-substring (point)
-                                     (progn
-                                       (move-to-column
-                                        (calculate-c-indent-within-comment t)
-                                        t)
-                                       (point))))))
+
+                   (let ((line-width (progn (end-of-line) (current-column))))
+                     (beginning-of-line)
+                     (prog1
+                         (buffer-substring
+                          (point)
+
+                          ;; How shall we decide where the end of the
+                          ;; fill-prefix is?
+                          ;; calculate-c-indent-within-comment bases its value
+                          ;; on the indentation of previous lines; if they're
+                          ;; indented specially, it could return a column
+                          ;; that's well into the current line's text.  So
+                          ;; we'll take at most that many space, tab, or *
+                          ;; characters, and use that as our fill prefix.
+                          (let ((max-prefix-end
+                                 (progn
+                                   (move-to-column
+                                    (calculate-c-indent-within-comment t)
+                                    t)
+                                   (point))))
+                            (beginning-of-line)
+                            (skip-chars-forward " \t*" max-prefix-end)
+                            (point)))
+
+                       ;; If the comment is only one line followed by a blank
+                       ;; line, calling move-to-column above may have added
+                       ;; some spaces and tabs to the end of the line; the
+                       ;; fill-paragraph function will then delete it and the
+                       ;; newline following it, so we'll lose a blank line
+                       ;; when we shouldn't.  So delete anything
+                       ;; move-to-column added to the end of the line.  We
+                       ;; record the line width instead of the position of the
+                       ;; old line end because move-to-column might break a
+                       ;; tab into spaces, and the new characters introduced
+                       ;; there shouldn't be deleted.
+
+                       ;; If you can see a better way to do this, please make
+                       ;; the change.  This seems very messy to me.
+                       (delete-region (progn (move-to-column line-width)
+                                             (point))
+                                      (progn (end-of-line) (point))))))))
+
               (paragraph-start
                ;; Lines containing just a comment start or just an end
                ;; should not be filled into paragraphs they are next to.