Tab key is extremely slow on medium-large files when emmet.triggerExpansionOnTab is enabled

[xak2000]

Issue Type: Bug

When I open a large file (tried on .php and .html) and emmet.triggerExpansionOnTab option is enabled, then each pressing on TAB key (even on blank line) make my computer hung for about 1-2 seconds (depends on file size) with high CPU load.

This is true with current 1.33 version of VS CODE, with or without extensions (tried with code --disable-extensions), with or without project open. I also tried to download 1.34 insiders build and the behavior is still the same.

Steps to Reproduce:

1. Download a fresh 1.34 insiders build (or use 1.33 current).

2. Create new HTML file tmp.html with any content. Make sure it is 2000+ lines. Better 5000+ - the hang is more obvious when the file is more large. I attached an example file here.

3. Set cursor on any line and press TAB. You can press it many times in a row or press and hold - all should be fine.

4. Open preferences and enable Emmet: Trigger Expansion on Tab option (emmet.triggerExpansionOnTab).

5. Return to opened file and try to press TAB again. You should see a very notable delay between pressing the key and moving the cursor (you can enable Toggle render whitespace option to see this better).

   If you press and hold the TAB key for about 5 seconds, then you should see no spaces/tabs characters entered (but notice high CPU load), you then can move cursor to anoter place in the editor, and after another 10-30 seconds have been passed (all that time with high CPU load), the delayed space characters will appear at the current cursor position (not where the cursor been when you actually pressed the TAB key).

So here is two problems:

1. A high CPU load and delay between pressing TAB key and appearing of spaces/tab characters.
2. The space/tab characters appears after the delay not where the cursor was when TAB key was pressed, but at the current position of the cursor.

I notice this problem only recently. I'm not sure with which build this comes in (not used VS Code recently), but 1-2 month ago there were no this problem.

---

VS Code version: Code - Insiders 1.34.0-insider (56f1b47, 2019-04-09T05:19:45.294Z)
OS version: Windows_NT x64 6.1.7601

System Info

Item	Value
CPUs	Intel(R) Core(TM) i5-4670 CPU @ 3.40GHz (4 x 3400)
GPU Status	2d_canvas: enabled checker_imaging: disabled_off flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: disabled_software rasterization: enabled surface_synchronization: enabled_on video_decode: enabled webgl: enabled webgl2: enabled
Load (avg)	undefined
Memory (System)	23.93GB (1.39GB free)
Process Argv
Screen Reader	no
VM	0%

Extensions: none

[medzhidov]

I have the same problem with latest vscode.

[octref]

Duplicate of #70371. Try tomorrow's Insiders which should have the fix.

[xak2000]

@octref Tried today's insiders build. Nothing is changed.

I opened a html file with 3700 LOC, enabled emmet.triggerExpansionOnTab, and tried to press TAB. It extremely slow and consumes high CPU. For doing nothing (nothing to expand by emmet because I press TAB key on empty lines...).

Also, it can be not a duplicate of #70371 because in #70371 there is no high CPU load and there users try real emmet expansions. This bug on other hand not about emmet expansion, but about pressing TAB key on empty line (where emmet should not trigger at all). Not only on empty lines I must say, but on non-empty lines too.

It also has nothing to do with HTML. I tried to open a large PHP file and it has same problem.

VS Code version: Code - Insiders 1.37.0-insider (cf03ea3, 2019-07-30T07:15:22.972Z)
OS version: Windows_NT x64 6.1.7601

System Info

Item	Value
CPUs	Intel(R) Core(TM) i5-4670 CPU @ 3.40GHz (4 x 3400)
GPU Status	2d_canvas: enabled flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: disabled_software oop_rasterization: disabled_off protected_video_decode: unavailable_off rasterization: enabled skia_deferred_display_list: disabled_off skia_renderer: disabled_off surface_synchronization: enabled_on video_decode: enabled viz_display_compositor: disabled_off webgl: enabled webgl2: enabled
Load (avg)	undefined
Memory (System)	23.93GB (2.88GB free)
Process Argv
Screen Reader	no
VM	0%

Extensions: none

[octref]

It's not in insider yet. Wait a bit.

[medzhidov]

It's not in insider yet. Wait a bit.

Is a bit - you mean we have no chance to resolve this critycal for developer problem?)
This problem follows from when vscode released emmet from the box. We have no problem before, but now we have a lot of problem with default emmet - it does not support a lot of shortcuts from original emmet and have a lot of bugs by default installation.

I loved vscode and developed several extensions, but now i start thinking about sublime text 3 again.

[octref]

we have no chance to resolve

It's already resolved.

Is a bit

You can either build from source or wait for another release of Insiders version coming out this afternoon.

[xak2000]

@octref

I downloaded a fresh copy of VS Code Insiders (I inlcuded version and commit hash on bottom of this message) and still nothing changed.

As I see, the commit 99d5ff9, that fixes #70371 is from PR #78207 and it is already included in insiders build (at least it is below of the current commit of downloaded build on master branch. The Insiders build is built from master, right?).

So, if you meant that this commit should fix this issue, it doesn't, unfortunately. :-(

I record a video to show what it looks like: vc-code-slow-tab-and-high-cpu-usage2.zip. On 00:18 I pressed TAB key several times in a row and only on 00:43 the editor finally rendered all these spaces (in my case 4 spaces instead of "tab" character). Throughout its 25 seconds VS Code consumed 100% of a single CPU core, trying to render 10 TABs (I know, that it actually consumed the cpu for something else (Emmet I think), it's just a simplification).

The GIF version of the video:

---

VS Code version: Code - Insiders 1.37.0-insider (d5900c6, 2019-07-31T05:24:41.973Z)
OS version: Windows_NT x64 6.1.7601

System Info

Item	Value
CPUs	Intel(R) Core(TM) i5-4670 CPU @ 3.40GHz (4 x 3400)
GPU Status	2d_canvas: enabled flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing:

enabled
multiple_raster_threads: enabled_on
native_gpu_memory_buffers: disabled_software
oop_rasterization: disabled_off
protected_video_decode: unavailable_off
rasterization: enabled
skia_deferred_display_list: disabled_off
skia_renderer: disabled_off
surface_synchronization: enabled_on
video_decode: enabled
viz_display_compositor: disabled_off
webgl: enabled
webgl2: enabled|
|Load (avg)|undefined|
|Memory (System)|23.93GB (4.55GB free)|
|Process Argv||
|Screen Reader|no|
|VM|0%|

Extensions: none

[octref]

I'm on d5900c6 and here's what I see in a 5k line HTML file:

Whereas this is stable:

NVM, I just realized that your bug is you are having "emmet.triggerExpansionOnTab" and expanding on empty lines, whereas the bug I fixed was for "emmet.triggerExpansionOnTab": false.

[DerrikMilligan]

This is indeed a bug, thanks for narrowing it down to the setting for me to turn off to at least live while it's being worked on.

[octref]

I made a cheap improvement, which is to disable expansion if the previous character is space or tab. For example div| expands, but div | doesn't. This makes tabbing on empty lines not that miserable, but a proper fix is still needed for the expansion.

[octref]

I'll switch to our html languageservice parser for December.

[rzhao271]

@xak2000 @andremacola @medzhidov does this issue occur for you in the latest vscode?
I know this issue hasn't been looked at for a year, and I want to see where things are at, now.
I noticed that pressing and holding down tab is causing a bunch of events to fire in the profile, though I haven't associated any directly with Emmet yet.
Will take a closer look tomorrow.

[medzhidov]

Don't worry, i started use PHPStorm, so this bug can be leaved for another one year =)

[xak2000]

@rzhao271 I checked out the file tmp.html that I included in the issue description and no, it doesn't occur anymore if I press and hold TAB on an empty line.

But I managed to reproduce the issue in other way.

1. Open preferences and enable Emmet: Trigger Expansion on Tab option (emmet.triggerExpansionOnTab).
2. Put the cursor at the start of an empty line of tmp.html file (e.g. on line 11).
3. Enter div and press Esc to close the autocompletion popup menu.
4. Press and hold TAB for 5-10 seconds. Release it.
5. Nothing new will be entered in the editor (emmet expansion would not happen) in next 10-20 seconds (one expansion sometimes still happens so one instance of <tab></tab> text could appear), but you will notice one CPU thread that consume 100% CPU. Main editor thread is still responsive, I suppose. I can move cursor to another line and enter some new text here etc. It looks like VS Code is not frozen at all. To notice that something is wrong I needed to look at my CPU temperature and frequency and I see that it doing some hard work. And then after 10-20 seconds suddenly emmet will finish it's expansion and something like this will be printed in the editor at the location of cursor when you held TAB:

<div>|</div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>v></div>

(the | indicates the cursor location).

And what is worse: cursor will be moved back into the position of the file when you held TAB (after first <div>). Even if you already was in another place of the file and entering some text at the moment, your input will be interrupted and part of text that you entered will be placed into the new position of cursor (after first <div>).

[rzhao271]

\closedWith 15ba9ae