Repository: vscode
Issue: Opening merge editor for a file takes incredibly long
Labels: bug,freeze-slow-crash-leak,merge-editor

Type: <b>Bug</b>

Hello, Team!

When trying to open the file in the attachment (change extension to .nswag) for merging, it takes an incredibly long time (see attached gif, the loading went on for several more minutes until I shut it off). I know it is a relatively large text file, but even then it should not take this amount of time.

[webapi_client.txt](https://github.com/microsoft/vscode/files/10412292/webapi_client.txt)
[MergeEditorTakesTooLong](https://user-images.githubusercontent.com/1839739/212344450-9ab92717-57ae-40ac-b470-888d7d4b24eb.gif)

VS Code version: Code 1.74.3 (97dec172d3256f8ca4bfb2143f3f76b503ca0534, 2023-01-09T16:59:02.252Z)
OS version: Windows_NT x64 10.0.19045
Modes:
Sandboxed: No


<details>
<summary>System Info</summary>

|Item|Value|
|---|---|
|CPUs|11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz (8 x 2803)|
|GPU Status|2d_canvas: enabled<br>canvas_oop_rasterization: disabled_off<br>direct_rendering_display_compositor: disabled_off_ok<br>gpu_compositing: enabled<br>multiple_raster_threads: enabled_on<br>opengl: enabled_on<br>rasterization: enabled<br>raw_draw: disabled_off_ok<br>skia_renderer: enabled_on<br>video_decode: enabled<br>video_encode: enabled<br>vulkan: disabled_off<br>webgl: enabled<br>webgl2: enabled<br>webgpu: disabled_off|
|Load (avg)|undefined|
|Memory (System)|31.75GB (4.87GB free)|
|Process Argv|--crash-reporter-id c2d76645-3789-47da-a678-f1fbfbb015bc|
|Screen Reader|no|
|VM|0%|
</details><details><summary>Extensions (36)</summary>

Extension|Author (truncated)|Version
---|---|---
project-manager|ale|12.7.0
ng-template|Ang|15.1.0
gitstash|art|5.1.0
asciidoctor-vscode|asc|2.9.8
vscode-tailwindcss|bra|0.9.5
npm-intellisense|chr|1.4.4
path-intellisense|chr|2.8.4
gitignore|cod|0.9.0
font-preview|ctc|2.2.1
vscode-eslint|dba|2.2.6
githistory|don|0.6.19
gitlens|eam|13.2.0
vscode-html-css|ecm|1.13.1
EditorConfig|Edi|0.16.4
prettier-vscode|esb|9.10.4
vscode-firefox-debug|fir|2.9.8
code-runner|for|0.11.8
angular-essentials|joh|13.0.0
Angular2|joh|13.0.0
vscode-peacock|joh|4.2.2
git-graph|mhu|1.30.0
vscode-scss|mrm|0.10.0
vscode-docker|ms-|1.23.3
csharp|ms-|1.25.2
remote-containers|ms-|0.266.1
material-icon-theme|PKi|4.23.1
tsimporter|pmn|2.0.1
vscode-xml|red|0.23.0
svg-preview|Sim|2.8.3
vscode-csstree|sme|1.1.0
sonarlint-vscode|Son|3.13.0
code-spell-checker|str|2.14.0
move-ts|str|1.12.0
vscode-icons|vsc|12.0.1
gitblame|wad|10.1.0
vscode-open-in-github|ziy|1.3.6

(1 theme extensions excluded)

</details><details>
<summary>A/B Experiments</summary>

```
vsliv368:30146709
vsreu685:30147344
python383cf:30185419
vspor879:30202332
vspor708:30202333
vspor363:30204092
vslsvsres303:30308271
pythonvspyl392:30443607
vserr242cf:30382550
pythontb:30283811
vsjup518:30340749
pythonptprofiler:30281270
vshan820:30294714
vstes263:30335439
vscorecescf:30445987
pythondataviewer:30285071
vscod805:30301674
binariesv615:30325510
bridge0708:30335490
bridge0723:30353136
cmake_vspar411:30581797
vsaa593:30376534
pythonvs932:30410667
cppdebug:30492333
vsclangdc:30486549
c4g48928:30535728
dsvsc012cf:30540253
azure-dev_surveyone:30548225
pyindex848:30577860
nodejswelcome1:30587005
282f8724:30602487
f6dab269:30613381
fim-prod:30623723

```

</details>

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