Much lag for large files (>4000 lines)

[molgrum]

As the title says, tested on Windows 10. It is very tedious to work because every character I type has 1-2 second delay to it. If more info is needed I can do profiling.

[srt19170]

Ditto.

[dgutov]

Please try:

(setq blink-matching-paren nil)

[srt19170]

That seems to have fixed the problem for me (or at least so far!) Thanks!

[srt19170]

Although the blink-matching-paren fixed some issues, I'm still having problems with large files. Doing a profile during a couple of long hangs revealed these as the top CPU users:

+ completion-pcm--all-completions                                  25   2%
+ js2-get-token                                                    28   2%
+ js2-parse-member-expr-tail                                       30   2%
+ js2-visit-ast                                                    56   4%
+ js2-match-token                                                  56   4%
+ js2-skip-line                                                    77   6%
+ js2-get-token-internal-1                                        128  10%
+ js2-get-token-internal                                          172  13%
  Automatic GC                                                    183  14%

This might be slow even without the GCs, but it seems like something in get-token-internal is creating a lot of garbage?

[dgutov]

Just how large are the files we are talking about?

[srt19170]

The one I ran the profile on is 6000 lines. I can provide it to you (offline) for testing if that would help.

[dgutov]

Before we do that, have you tried reproducing the problem starting with emacs -Q?

The scenario would look something like this:

emacs -Q -L ~/.emacs.d/elpa/js2-mode-???/
(require 'js2-mode)
find-file ....
M-x js2-mode
(your steps here)

[srt19170]

Yes, I get the same behavior in -Q.

[dgutov]

All right, please send me the file. My email is at the top of js2-mode.el.

[dgutov]

Thanks, I see it there. Seeing as the reproduction scenario involves typing characters from electric-indent-chars, electric-indent-mode (on by default) is involved.

Ultimately, it's a bug in js--multi-line-declaration-indentation caused by a faulty translation from js2-mode indentation code. You can apply this patch to your Emacs:

diff --git a/lisp/progmodes/js.el b/lisp/progmodes/js.el
index 6d995a0..0ba7aac 100644
--- a/lisp/progmodes/js.el
+++ b/lisp/progmodes/js.el
@@ -1851,7 +1851,8 @@ js--multi-line-declaration-indentation
   "Helper function for `js--proper-indentation'.
 Return the proper indentation of the current line if it belongs to a declaration
 statement spanning multiple lines; otherwise, return nil."
-  (let (at-opening-bracket)
+  (let (forward-sexp-function ; use Lisp version even in js2-mode
+        at-opening-bracket)
     (save-excursion
       (back-to-indentation)
       (when (not (looking-at js--declaration-keyword-re))

And I'll try to get it into the upcoming Emacs release (25.2).

[srt19170]

I'm not sure how I'm "supposed" to patch Emacs, but putting a fixed version of the function into my .emacs file seemed to work, because the hangup is now gone.

Thanks a bunch, Dmitri! Really appreciate the effort!

[dgutov]

I'm not sure how I'm "supposed" to patch Emacs

You apply the patch the sources, and rebuild. 😛 If Emacs was built by your distribution, it's harder, of course.

putting a fixed version of the function into my .emacs file seemed to work

That works as well. And yet another option is to define an around-advice for this function, with a let-binding for the aforementioned variable.

You're welcome!

[dgutov]

get it into the upcoming Emacs release (25.2)

And done.