MyCompletionItem is expensive

[jrieken]

This is a follow-up from microsoft/TypeScript#36265 (comment)

• see attached profile CPU-20200415T102048.875Z.cpuprofile.txt
• the creation of MyCompletionItem is taking quite some time and sums up to more than the actual completion request

Also, it calls getWordRangeAtPosition after completions have arrived and therefore on a potentially different state, with different words etc. This should be all before

[jrieken]

related to #95325

[mjbvz]

getReplaceRange

vscode/extensions/typescript-language-features/src/features/completions.ts

Line 181 in ce57f8a

private getReplaceRange(line: string) {

is the most expensive part of this call

Now that microsoft/TypeScript#29270 is fixed, I believe I can just disable this branch for TS 3.9+

[mjbvz]

In a empty js file, I now see the TS extension's completion conversion take around 25ms (down from around 50ms on my machine):

@jrieken Let me know if you notice any other obvious optimization opportunities.

[jrieken]

Look at this: The memoize util is responsible for 15-20% of the time it takes to convert completion items.

You are better off nuking that using a good old field. I also believe (measure, this used to be true is the past when I measured that) that computation is faster if you use static maps instead of switch-case-statements. So, have staticMap[entryKind] instead of the switch-case (the same would then be true convertKind)

[mjbvz]

Good catch. Removing memo does improve _convert

The static map performs the same (or perhaps slightly worse) than the switch. I tested it by looping though a completion list 1000 times and converting the kind of every entry in it

[jrieken]

Thanks