bug#35316: 26.2; Emacs lags in c++-mode buffer when editing with iedit-mode on

[Alan Mackenzie <acm@muc.de>]

Hello, Amos and Zhang.

First thing, apologies for the patch I sent you a few days ago.  It was
based on a misunderstanding, and it is total garbage!

The misunderstanding was the assumption that
`inhibit-modification-hooks' would be nil on entry to
`iedit-update-occurrences-2', and that leaving it nil would allow the
`before-change-functions' and `after-change-functions' hooks to run
normally.

In actual fact `inhibit-modification-hooks' is t at that point, and
cannot successfully be bound to nil.  So, both `before-change-functions'
and `after-change-functions' need to be called explicitly for successful
processing.

So, please disregard that previous patch from me, and try out instead
the patch below.  In C++ Mode it is somewhat slower, since it is
actually doing the change processing, but not unusably so.  Undo seems
to be working a bit faster too, though it is often not instantaneous as
one would wish (see below).

On Sat, May 18, 2019 at 01:35:58 +0800, Amos Bird wrote:

> Hi Alan!

> > Are we still talking about C++ Mode

> Yeah it's c++ mode but it can also be reproduced with c mode.
> The minute long frozen is caused mainly by the lsp-mode, howeveer
> it's still laggy after turning lsp off.

> > How big is your file?  Can you characterise it in any way?

> You can try emacs/src/xdisp.c . iediting all "make_fixnum",
> turning them into "make_fixnum_why_undo_redo_is_so_slow", and 
> undo.
> It's about 10-20 seconds freezing time here.

When I do this now (with the patch in place), undo works in two stages,
taking about 0.4s and 2.4s respectively on my machine.

> > It seems I have more work to do on this in any case.

As a matter of interest, could one of you please give me the name and
email address of the iedit-mode maintainer.  I haven't got a github
account, and don't want to create one, so I don't think I can get in
touch with her/him that way.

> Looking forward to it!

OK, here goes!



--- iedit-lib.el.orig	2019-05-19 10:55:31.681959998 +0000
+++ iedit-lib.el	2019-05-19 11:08:27.549988930 +0000
@@ -490,7 +490,9 @@
 
 (defun iedit-update-occurrences-2 (occurrence after beg end &optional change)
   ""
-  (let ((inhibit-modification-hooks t)
+  (let (;; (inhibit-modification-hooks t)
+        ;; Note: `inhibit-modification-hook' will already be non-nil when this
+	;; function is called.  Setting it to nil here doesn't work.
         (offset (- beg (overlay-start occurrence)))
         (value (buffer-substring-no-properties beg end)))
     (save-excursion
@@ -501,6 +503,9 @@
                    (ending (+ beginning (- end beg))))
               (when (not (eq another-occurrence occurrence))
                 (goto-char beginning)
+		(run-hook-with-args 'before-change-functions
+				    beginning
+				    (+ beginning change))
                 (insert-and-inherit value)
                 ;; todo: reconsider this change Quick fix for
                 ;; multi-occur occur-edit-mode: multi-occur depend on
@@ -517,13 +522,17 @@
         ;; deletion
         (dolist (another-occurrence (remove occurrence iedit-occurrences-overlays))
           (let ((beginning (+ (overlay-start another-occurrence) offset)))
+	    (goto-char beginning)
+	    (run-hook-with-args 'before-change-functions
+				beginning
+				(+ beginning change))
             (delete-region beginning (+ beginning change))
             (unless (eq beg end) ;; replacement
               (goto-char beginning)
               (insert-and-inherit value))
             (run-hook-with-args 'after-change-functions
                                 beginning
-                                (+ beginning (- beg end))
+                                (+ beginning (- end beg))
                                 change)))))))
 
 (defun iedit-next-occurrence ()


> regards,

> --
> Amos Bird
> amosbird@gmail.com

-- 
Alan Mackenzie (Nuremberg, Germany).