Slow to open a Go file with long line

[egonelbre]

Issue Type: Performance Issue

File https://gist.githubusercontent.com/egonelbre/f93be4d31e7f4dad766a5e8f63374bb3/raw/747cf854bef769e3b8f57edbe207e4e001d98421/example.go is very slow to open. ~20s

This does not happen when file is renamed to example.c.

VS Code version: Code 1.40.2 (f359dd69833dd8800b54d458f6d37ab7c78df520, 2019-11-25T14:52:45.129Z) OS version: Darwin x64 19.2.0

System Info

|Item|Value| |---|---| |CPUs|Intel(R) Core(TM) i5-5257U CPU @ 2.70GHz (4 x 2700)| |GPU Status|2d_canvas: enabled
flash_3d: enabled
flash_stage3d: enabled
flash_stage3d_baseline: enabled
gpu_compositing: enabled
metal: disabled_off
multiple_raster_threads: enabled_on
oop_rasterization: disabled_off
protected_video_decode: unavailable_off
rasterization: enabled
skia_renderer: disabled_off
surface_control: disabled_off
surface_synchronization: enabled_on
video_decode: enabled
viz_display_compositor: enabled_on
viz_hit_test_surface_layer: disabled_off
webgl: enabled
webgl2: enabled| |Load (avg)|3, 4, 3| |Memory (System)|8.00GB (0.10GB free)| |Process Argv|| |Screen Reader|no| |VM|0%|

Workspace Info

``` | Window (~/code/adventofcode >) | Folder (adventofcode): 63 files | File types: go(43) gitignore(1) mod(1) js(1) json(1) md(1) | Conf files: settings.json(1); ```

Extensions (6)

Extension|Author (truncated)|Version ---|---|--- gotemplate|cas|0.3.0 dart-code|Dar|3.7.0 vue|jcb|0.1.5 csharp|ms-|1.21.8 proto|pet|0.0.2 vscode-svg-previewer|vit|0.5.1

Profiling seems to indicate Go syntax highlighting is hitting a bad-case.

[egonelbre]

https://github.com/microsoft/vscode/issues/82549 could end up fixing this as a side-effect.

[egonelbre]

Profiling seems to indicate that the parsing time is growing non-linearly, which isn't great.

size	time
~5K	~2.5s
~10K	~9s
~15K	~20s
~19K	~34s

[egonelbre]

The main culprit seems to be "match": "(?<!var)\\s*(\\w+(?:\\.\\w+)*(?>,\\s*\\w+(?:\\.\\w+)*)*)(?=\\s*=(?!=))", at https://github.com/microsoft/vscode/blob/master/extensions/go/syntaxes/go.tmLanguage.json#L231

Removal improvement: 15.1s -> 3.6s.

The second culprit is "match": "(\\bfunc\\b)|(\\w+)(?=\\()", at https://github.com/microsoft/vscode/blob/master/extensions/go/syntaxes/go.tmLanguage.json#L130

Changing to \\bfunc\\b improved from 3.6s -> 0.006s.

I also tried opening the same file with Atom so it doesn't seem like a problem in https://github.com/atom/language-go.

PS: I'm aware the changes aren't correct, but they demonstrate the performance issue.

[alexr00]

Thank you for the detail investigation!

Atom doesn't use the textmate grammar at https://github.com/atom/language-go anymore, so issues with the textmate grammar that VS Code uses likely won't occur there.

Since atom is no longer making changes to the textmate grammar, #82549 is the best hope for fixing this.

[vscodebot[bot]]

Thanks for creating this issue! We figured it's covering the same as another one we already have. Thus, we closed this one as a duplicate. You can search for existing issues here. See also our issue reporting guidelines.

Happy Coding!