Re: perl mode color highlighting working badly

[Stefan Monnier]

> I knew the file alone wouldn't be enough. So I can try and explain what I do
> to see the problems.

Can you try the patch below and tell me if it improves anything?
And if so, at what performance cost (it only costs to perl-mode buffers)?


        Stefan


--- orig/lisp/progmodes/perl-mode.el
+++ mod/lisp/progmodes/perl-mode.el
@@ -534,6 +534,7 @@
                              . perl-font-lock-syntactic-keywords)
                             (font-lock-syntactic-face-function
                              . perl-font-lock-syntactic-face-function)
+                             (font-lock-fontify-syntactically-eagerly . t)
                             (parse-sexp-lookup-properties . t)))
   ;; Tell imenu how to handle Perl.
   (set (make-local-variable 'imenu-generic-expression)

--- orig/lisp/font-lock.el
+++ mod/lisp/font-lock.el
@@ -1033,6 +1033,12 @@
 Useful for things like RMAIL and Info where the whole buffer is not
 a very meaningful entity to highlight.")
 
+(defvar font-lock-fontify-syntactically-eagerly nil
+  "If non-nil, `font-lock-fontify-syntactically-region' is applied to 
non-displayed text.
+For modes which set syntax-table properties from
+`font-lock-syntactic-face-function', it may be necessary to also apply
+`font-lock-fontify-syntactically-region' on all the buffer before point.")
+
 (defun font-lock-default-fontify-region (beg end loudly)
   (save-buffer-state
       ((parse-sexp-lookup-properties
@@ -1064,11 +1070,23 @@
           (unless (bolp) (setq end (line-beginning-position 2)))
          ;; Now do the fontification.
          (font-lock-unfontify-region beg end)
-         (when font-lock-syntactic-keywords
-           (font-lock-fontify-syntactic-keywords-region beg end))
-         (unless font-lock-keywords-only
-           (font-lock-fontify-syntactically-region beg end loudly))
-         (font-lock-fontify-keywords-region beg end loudly))
+          (let ((sbeg beg))
+            ;; Ensure the beginning of the file is properly 
syntactic-fontified.
+            (when (and font-lock-syntactically-fontified
+                       (< font-lock-syntactically-fontified sbeg))
+              (setq sbeg (max font-lock-syntactically-fontified (point-min)))
+              (setq font-lock-syntactically-fontified end))
+            (when font-lock-syntactic-keywords
+              (font-lock-fontify-syntactic-keywords-region sbeg end))
+            (unless font-lock-keywords-only
+              (font-lock-fontify-syntactically-region
+               ;; For modes which set syntax-table properties from
+               ;; font-lock-syntactic-face-function, it may be necessary to
+               ;; also apply font-lock-fontify-syntactically-region on all
+               ;; the buffer before point.
+               (if font-lock-fontify-syntactically-eagerly sbeg beg)
+               end loudly)))
+          (font-lock-fontify-keywords-region beg end loudly))
       ;; Clean up.
       (set-syntax-table old-syntax-table))))
 
@@ -1282,11 +1300,6 @@
 (defun font-lock-fontify-syntactic-keywords-region (start end)
   "Fontify according to `font-lock-syntactic-keywords' between START and END.
 START should be at the beginning of a line."
-  ;; Ensure the beginning of the file is properly syntactic-fontified.
-  (when (and font-lock-syntactically-fontified
-            (< font-lock-syntactically-fontified start))
-    (setq start (max font-lock-syntactically-fontified (point-min)))
-    (setq font-lock-syntactically-fontified end))
   ;; If `font-lock-syntactic-keywords' is a symbol, get the real keywords.
   (when (symbolp font-lock-syntactic-keywords)
     (setq font-lock-syntactic-keywords (font-lock-eval-keywords