Redundant font-locking in comint buffers

[Stefan Monnier]

Text in comint buffers (especially prompts and input text) tends to be
re-fontified excessively because comint adds/removes text-properties
on them frequently, which is always considered as a buffer-modification
and thus triggers font-lock.

This is generally a minor issue of performance, especially with jit-lock
which delays the font-locking until display, thus bundling most of the
redundant re-fontification into a single one.  But if you use
compilation-shell-minor-mode, then the redundant fontification becomes more
noticeable because jit-lock is turned off and because font-lock does
more work.

So I suggest the patch below which wraps all the text-property manipulation
inside `inhibit-modification-hooks' to make sure font-lock will not be
unnecessarily triggered.

Any objection?


        Stefan


--- orig/lisp/comint.el
+++ mod/lisp/comint.el
@@ -1482,7 +1482,8 @@
                                (concat input "\n")))
 
          (let ((beg (marker-position pmark))
-               (end (if no-newline (point) (1- (point)))))
+             (end (if no-newline (point) (1- (point))))
+             (inhibit-modification-hooks t))
            (when (> end beg)
              ;; Set text-properties for the input field
              (add-text-properties
@@ -1578,7 +1576,8 @@
 freeze its attributes in place, even when more input comes a long
 and moves the prompt overlay."
   (when comint-last-prompt-overlay
-    (let ((inhibit-read-only t))
+    (let ((inhibit-read-only t)
+         (inhibit-modification-hooks t))
       (add-text-properties (overlay-start comint-last-prompt-overlay)
                            (overlay-end comint-last-prompt-overlay)
                            (overlay-properties comint-last-prompt-overlay)))))
@@ -1709,7 +1708,8 @@
            (goto-char (process-mark process)) ; in case a filter moved it
 
            (unless comint-use-prompt-regexp-instead-of-fields
-              (let ((inhibit-read-only t))
+              (let ((inhibit-read-only t)
+                   (inhibit-modification-hooks t))
                 (add-text-properties comint-last-output-start (point)
                                      '(rear-nonsticky t
                                       field output
@@ -1718,7 +1718,8 @@
            ;; Highlight the prompt, where we define `prompt' to mean
            ;; the most recent output that doesn't end with a newline.
            (let ((prompt-start (save-excursion (forward-line 0) (point)))
-                 (inhibit-read-only t))
+                 (inhibit-read-only t)
+                 (inhibit-modification-hooks t))
              (when comint-prompt-read-only
                (or (= (point-min) prompt-start)
                    (get-text-property (1- prompt-start) 'read-only)
@@ -2347,7 +2354,8 @@
 If the character after point does not have a front-sticky
 read-only property, any read-only property of `fence' on the
 preceding newline is removed."
-  (let* ((pt (point)) (lst (get-text-property pt 'front-sticky)))
+  (let* ((pt (point)) (lst (get-text-property pt 'front-sticky))
+        (inhibit-modification-hooks t))
     (and (bolp)
         (not (bobp))
         (if (and (get-text-property pt 'read-only)