`formatWithCursor` hangs/takes several seconds on text HTML input

[abose]

Hi all,

I was integrating prettier as a default extension in brackets editor. using formatWithCursor API to prettify code leads to hangs and general slowness.
Prettier is hosted in web worker inside brackets. formatWithCursor API is causing large delays and hangs in most large html files, but normal format api works just fine.

• Attached zip project with samples files that causing hangs. pretty.zip
• Also see this URL in dev tools to see a quick simple use case that hangs for several seconds in beautify API.

questions

• I could not find the use of formatWithCursor in vscode extension code. How does the vscode extension handle cursor movement without using the API.
• Is formatWithCursor recommended for usage within editors as i am seeing several seconds of delay to prettify code in not so large attached sample files.

Any help would be much appreciated.

Environments:

• Prettier Version: 2.7.1
• Running Prettier via: Browser API
• Runtime: Chrome v83, web worker
• Operating System: Linux
• Prettier plugins (if any): parser-html.js

Steps to reproduce:

• Extract the contents of pretty.zip
• open index.html in any editor and see debugger. observe that the main thread hangs for several seconds on calling formatWithCursor.

Expected behavior:

• Gets result with cursor

Actual behavior:

• hangs browser

Thanks,
Arun

[thorn0]

Unfortunately, formatWithCursor has known performance issues. See #4801

VS Code somehow manages the cursor itself, so formatter extensions don't need to care about it.

[thorn0]

Duplicate of #4801

[abose]

Thanks for the quick reply @thorn0 . looks like there are no quick solutions. I tried using our own diffs but the performance on large files were not acceptable too.

Vscode repo should have some answers on how they do it so well without the performance penalty of diffs. Maybe they are using the parse tree path im guessing. Will update if I find anything.

[thorn0]

You might want to try the solution proposed in #6164