(comment-choose-indent): New function extracted

from comment-indent.  Improve the alignment algorithm.
(comment-indent): Use it.

2 files changed, 77 insertions, 47 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 2f59072e23f..e2b68f2b617 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,9 @@
+2007-09-28  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+        * newcomment.el (comment-choose-indent): New function extracted
+        from comment-indent.  Improve the alignment algorithm.
+        (comment-indent): Use it.
+
 2007-09-27  Juanma Barranquero  <lekktu@gmail.com>
 
         * emacs-lisp/eldoc.el (eldoc-message-commands-table-size)
@@ -8,7 +14,7 @@
 
 2007-09-26  Eli Zaretskii  <eliz@gnu.org>
 
-        * menu-bar.el (menu-bar-search-documentation-menu): Renamed from
+        * menu-bar.el (menu-bar-search-documentation-menu): Rename from
         menu-bar-apropos-menu.  All users changed.
         (menu-bar-help-menu): Change menu symbols to better match the text
         displayed by the menu.
@@ -31,8 +37,8 @@
 
 2007-09-24  Ville Skytt,Ad(B  <scop@xemacs.org>  (tiny change)
 
-        * net/tramp-vc.el (tramp-vc-user-login-name): Use
-        `vc-find-version' instead of `process-file' to check whether we
+        * net/tramp-vc.el (tramp-vc-user-login-name):
+        Use `vc-find-version' instead of `process-file' to check whether we
         have a new enough vc that doesn't need the defadvice.
 
 2007-09-23  Dan Nicolaescu  <dann@ics.uci.edu>
@@ -75,16 +81,15 @@
 
 2007-09-22  Glenn Morris  <rgm@gnu.org>
 
-        * eshell/esh-mode.el (eshell-output-filter-functions): Add
-        eshell-postoutput-scroll-to-bottom.
+        * eshell/esh-mode.el (eshell-output-filter-functions):
+        Add eshell-postoutput-scroll-to-bottom.
 
 2007-09-21  Dan Nicolaescu  <dann@ics.uci.edu>
 
-        * files.el (file-name-sans-versions): Allow - and a-z in version
-        names.
+        * files.el (file-name-sans-versions): Allow - and a-z in version names.
 
-        * log-view.el (log-view-mode-map, log-view-mode-menu): Bind
-        log-view-annotate-version.
+        * log-view.el (log-view-mode-map, log-view-mode-menu):
+        Bind log-view-annotate-version.
         (log-view-beginning-of-defun, log-view-end-of-defun)
         (log-view-annotate-version): New functions.
         (log-view-mode): Use log-view-beginning-of-defun and
@@ -92,7 +97,7 @@
 
 2007-09-21  Stefan Monnier  <monnier@iro.umontreal.ca>
 
-        * emacs-lisp/easy-mmode.el (define-minor-mode): Fix staging brain damage.
+        * emacs-lisp/easy-mmode.el (define-minor-mode): Fix staging.
 
 2007-09-21  Kevin Ryde  <user42@zip.com.au>
 
diff --git a/lisp/newcomment.el b/lisp/newcomment.el
index 63ceacb0440..9c6be255023 100644
--- a/lisp/newcomment.el
+++ b/lisp/newcomment.el
@@ -97,10 +97,10 @@ Major modes should set this variable.")
 ;;;###autoload
 (defcustom comment-column 32
   "Column to indent right-margin comments to.
-Each mode establishes a different default value for this variable; you
+Each mode may establish a different default value for this variable; you
 can set the value for a particular mode using that mode's hook.
-Comments might be indented to a value smaller than this in order
-not to go beyond `comment-fill-column'."
+Comments might be indented to a different value in order not to go beyond
+`comment-fill-column' or in order to align them with surrounding comments."
   :type 'integer
   :group 'comment)
 (make-variable-buffer-local 'comment-column)
@@ -194,7 +194,7 @@ two semi-colons.")
     (extra-line . (t nil t t))
     (box        . (nil t t t))
     (box-multi  . (t t t t)))
-  "Possible comment styles of the form (STYLE . (MULTI ALIGN EXTRA INDENT)).
+  "Comment region styles of the form (STYLE . (MULTI ALIGN EXTRA INDENT)).
 STYLE should be a mnemonic symbol.
 MULTI specifies that comments are allowed to span multiple lines.
 ALIGN specifies that the `comment-end' markers should be aligned.
@@ -208,7 +208,8 @@ INDENT specifies that the `comment-start' markers should not be put at the
   "Style to be used for `comment-region'.
 See `comment-styles' for a list of available styles."
   :type (if (boundp 'comment-styles)
-            `(choice ,@(mapcar (lambda (s) `(const ,(car s))) comment-styles))
+            `(choice ,@(mapcar (lambda (s) `(const ,(car s)))
+                               comment-styles))
           'symbol)
   :group 'comment)
 
@@ -516,6 +517,58 @@ Point is assumed to be just at the end of a comment."
               (and (> comment-add 0) (looking-at "\\s<\\(\\S<\\|\\'\\)")))
       comment-column)))
 
+(defun comment-choose-indent (&optional indent)
+  "Choose the indentation to use for a right-hand-side comment.
+The criteria are (in this order):
+- try to keep the comment's text within `comment-fill-column'.
+- try to align with surrounding comments.
+- prefer INDENT (or `comment-column' if nil).
+Point is expected to be at the start of the comment."
+  (unless indent (setq indent comment-column))
+  ;; Avoid moving comments past the fill-column.
+  (let ((max (+ (current-column)
+                (- (or comment-fill-column fill-column)
+                   (save-excursion (end-of-line) (current-column)))))
+        (other nil)
+        (min (save-excursion (skip-chars-backward " \t")
+                             (1+ (current-column)))))
+    ;; Fix up the range.
+    (if (< max min) (setq max min))
+    ;; Don't move past the fill column.
+    (if (<= max indent) (setq indent max))
+    ;; We can choose anywhere between min..max.
+    ;; Let's try to align to a comment on the previous line.
+    (save-excursion
+      (when (and (zerop (forward-line -1))
+                 (setq other (comment-search-forward
+                              (line-end-position) t)))
+        (goto-char other) (setq other (current-column))))
+    (if (and other (<= other max) (>= other min))
+        ;; There is a comment and it's in the range: bingo!
+        other
+      ;; Can't align to a previous comment: let's try to align to comments
+      ;; on the following lines, then.  These have not been re-indented yet,
+      ;; so we can't directly align ourselves with them.  All we do is to try
+      ;; and choose an indentation point with which they will be able to
+      ;; align themselves.
+      (save-excursion
+        (while (and (zerop (forward-line 1))
+                    (setq other (comment-search-forward
+                                 (line-end-position) t)))
+          (goto-char other)
+          (let ((omax (+ (current-column)
+                         (- (or comment-fill-column fill-column)
+                            (save-excursion (end-of-line) (current-column)))))
+                (omin (save-excursion (skip-chars-backward " \t")
+                                      (1+ (current-column)))))
+            (if (and (>= omax min) (<= omin max))
+                (progn (setq min (max omin min))
+                       (setq max (min omax max)))
+              ;; Can't align with this anyway, so exit the loop.
+              (goto-char (point-max))))))
+      ;; Return the closest point to indent within min..max.
+      (max min (min max indent)))))
+
 ;;;###autoload
 (defun comment-indent (&optional continue)
   "Indent this line's comment to `comment-column', or insert an empty comment.
@@ -569,38 +622,9 @@ If CONTINUE is non-nil, use the `comment-continue' markers if any."
       (if (not indent)
           ;; comment-indent-function refuses: delegate to line-indent.
           (indent-according-to-mode)
-        ;; If the comment is at the left of code, adjust the indentation.
+        ;; If the comment is at the right of code, adjust the indentation.
         (unless (save-excursion (skip-chars-backward " \t") (bolp))
-          ;; Avoid moving comments past the fill-column.
-          (let ((max (+ (current-column)
-                        (- (or comment-fill-column fill-column)
-                           (save-excursion (end-of-line) (current-column))))))
-            (if (<= max indent)
-                (setq indent max)       ;Don't move past the fill column.
-              ;; We can choose anywhere between indent..max.
-              ;; Let's try to align to a comment on the previous line.
-              (let ((other nil)
-                    (min (max indent
-                              (save-excursion (skip-chars-backward " \t")
-                                              (1+ (current-column))))))
-                (save-excursion
-                  (when (and (zerop (forward-line -1))
-                             (setq other (comment-search-forward
-                                         (line-end-position) t)))
-                    (goto-char other) (setq other (current-column))))
-                (if (and other (<= other max) (>= other min))
-                    ;; There is a comment and it's in the range: bingo.
-                    (setq indent other)
-                  ;; Let's try to align to a comment on the next line, then.
-                  (let ((other nil))
-                    (save-excursion
-                      (when (and (zerop (forward-line 1))
-                                 (setq other (comment-search-forward
-                                             (line-end-position) t)))
-                        (goto-char other) (setq other (current-column))))
-                    (if (and other (<= other max) (> other min))
-                        ;; There is a comment and it's in the range: bingo.
-                        (setq indent other))))))))
+          (setq indent (comment-choose-indent indent)))
         ;; Update INDENT to leave at least one space
         ;; after other nonwhite text on the line.
         (save-excursion
@@ -1020,7 +1044,8 @@ The strings used as comment starts are built from
          (lines (nth 2 style))
          (block (nth 1 style))
          (multi (nth 0 style)))
-    ;; we use `chars' instead of `syntax' because `\n' might be
+
+    ;; We use `chars' instead of `syntax' because `\n' might be
     ;; of end-comment syntax rather than of whitespace syntax.
     ;; sanitize BEG and END
     (goto-char beg) (skip-chars-forward " \t\n\r") (beginning-of-line)