getOutliningSpans hangs on large, json-like file

[mjbvz]

From microsoft/vscode#60677

TypeScript Version: 3.2.0-dev.20181017

Search Terms:

• getOutliningSpans
• fold / folding

Code

1. Open this file javaScript file in VS Code: dict_en.txt

2. Notice that intellisense and other features do not work.

Bug
This is caused by the getOutliningSpans request never returning. We do try to cancel the request on the VS Code side when you switch away from that file but it seems the TS Server does not pick up the cancellation

Playground Link:

Related Issues:

[DanielRosenwasser]

We can possibly pick an aribtrary high count of nodes to traverse and check the cancellation token ever n nodes traversed.

[weswigham]

The cancellation token disk access is already throttled. We don't need to meter when we check it, we just need to check it more.

[sheetalkamat]

While at it I noticed that before carrying out operation we check for cancellation token and that is not throttled. (https://github.com/Microsoft/TypeScript/blob/master/src/server/session.ts#L556) we should use throttled cancellation token there as well.

[weswigham]

So I think this is actually a dupe of #28540, because I'm tracking us as being stuck inside subtype reduction in the checker most of the time. If that's so, we have two candidate fixes up already, #28707 and #28727.

[weswigham]

cc @ahejlsberg this case is a 6MB array literal.