* lisp/emacs-lisp/smie.el: Provide smarter auto-filling.

(smie-auto-fill): New function.
(smie-setup): Use it.

2 files changed, 39 insertions, 0 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 29cb0334fb0..581ddc3788e 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,9 @@
+2012-02-15  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+        * emacs-lisp/smie.el: Provide smarter auto-filling.
+        (smie-auto-fill): New function.
+        (smie-setup): Use it.
+
 2011-12-27  Vincent Belaïche  <vincentb1@users.sourceforge.net>
 
         * ses.el: The overall change is to add cell renaming, that is
diff --git a/lisp/emacs-lisp/smie.el b/lisp/emacs-lisp/smie.el
index cad7c8419b2..49ee051e62d 100644
--- a/lisp/emacs-lisp/smie.el
+++ b/lisp/emacs-lisp/smie.el
@@ -1539,6 +1539,38 @@ to which that point should be aligned, if we were to reindent it.")
           (save-excursion (indent-line-to indent))
         (indent-line-to indent)))))
 
+(defun smie-auto-fill ()
+  (let ((fc (current-fill-column))
+        (try-again nil))
+    (while (and fc (> (current-column) fc))
+      (cond
+       ((not (or (nth 8 (save-excursion
+                          (syntax-ppss (line-beginning-position))))
+                 (nth 8 (syntax-ppss))))
+        (save-excursion
+          (beginning-of-line)
+          (smie-indent-forward-token)
+          (let ((bsf (point))
+                (gain 0)
+                curcol)
+            (while (<= (setq curcol (current-column)) fc)
+              ;; FIXME?  `smie-indent-calculate' can (and often will)
+              ;; return a result that actually depends on the presence/absence
+              ;; of a newline, so the gain computed here may not be accurate,
+              ;; but in practice it seems to works well enough.
+              (let* ((newcol (smie-indent-calculate))
+                     (newgain (- curcol newcol)))
+                (when (> newgain gain)
+                  (setq gain newgain)
+                  (setq bsf (point))))
+              (smie-indent-forward-token))
+            (when (> gain 0)
+              (setq try-again)
+              (goto-char bsf)
+              (newline-and-indent)))))
+       (t (do-auto-fill))))))
+
+
 (defun smie-setup (grammar rules-function &rest keywords)
   "Setup SMIE navigation and indentation.
 GRAMMAR is a grammar table generated by `smie-prec2->grammar'.
@@ -1549,6 +1581,7 @@ KEYWORDS are additional arguments, which can use the following keywords:
   (set (make-local-variable 'smie-rules-function) rules-function)
   (set (make-local-variable 'smie-grammar) grammar)
   (set (make-local-variable 'indent-line-function) 'smie-indent-line)
+  (set (make-local-variable 'normal-auto-fill-function) 'smie-auto-fill)
   (set (make-local-variable 'forward-sexp-function)
        'smie-forward-sexp-command)
   (while keywords