IntelliSense slow down with large json file

Does this issue occur when all extensions are disabled?: Yes

• VS Code Version: 1.65.2
• OS Version: Ubuntu 20.04.4 LTS

IntelliSense slow down when I set value for compilerOptions->jsx option in tsconfig.json file. Without this option (after restart vscode) I get autocomplete suggestion less then 1 second, with compilerOptions->jsx I get suggestion after 3-4 seconds. CPU i5 8 cores, available RAM more than 10GB.

When initializing js/ts language features in progress IntelliSense work fast

Tried in 1.66.0-insider the result is the same

{
	"compilerOptions": {
		...
		"jsx": "react",
		...
	},
	"exclude": [...]
}

[gabritto]

I’ve been investigating this issue, and at least for the example large jsons provided here (by @steve-ross and the json files in @ryancwalsh’s paintcolornerd), it seems what is happening is that we’re taking too long to type check the very large array in the json file, because in those cases the kind of type checking/inference we do is quadratic on the size of the array literal. This affects intellisense because, in general, when you open or change something in your file that imports the large json, we have to type check it again, and it takes a while. So there’s a general slowdown on things like completions, updating errors/red squiggles, quickinfo, etc, that rely on having your file type checked.

• From the checker’s implementation side: This happens because, when we are trying to figure out the type of your json array literal, we start by getting the type of each of the json array’s elements, and then we try to union them one by one to get the type of the array. But in this process, when we get the type of an array’s element and try to add it to the union, we first check if that element’s type is already present in the union (more specifically, if it’s a subtype of some type already in the union). That process, in the case of this json array literal, turns out to be quadratic in the size of the array.

I’m now going to think about ways in which we could improve this.

[ryancwalsh]

I finally found this issue after days of this problem. I’d been disabling all of my VSC extensions trying to figure out why Intellisense got so slow for a project of mine.

I finally narrowed it down to this one line in a file: import megaColors from '../data/colornerd.json';

The JSON is 3 MB. Having that one line makes Intellisense unusably slow for the whole project.