bluz71
commented
4 years ago I managed to test a bunch of language servers.
Tests
Two tests were undertaken, counting the number of server-provided completion items when completing a language keyword and also when completing a library type.
| Language | Language Server | Keyword Matches | Type Matches |
|---|---|---|---|
| C++ | clangd |
100 |
100 |
| Dart | Analysis Server / Flutter 1.12 |
5,630 |
5,619 |
| Dart | Analysis Server / Flutter 1.17 |
26,789 |
26,777 |
| Go | gopls |
4 |
4 |
| JavaScript | Microsoft TypeScript LS | 1,449 |
1,203 |
| JavaScript | Sourcegraph JavaScript LS | 1,083 |
1,083 |
| Ruby | Solargraph | 4 |
3 |
| Rust | rust-analyzer |
206 |
206 |
| Swift | SourceKit-LSP | 33,216 |
33,216 |
| TypeScript | Microsoft TypeScript LS | 1,371 |
1,106 |
Findings
Dart Analysis Server via Flutter 1.17 is towards the very upper end in providing too many completion items. A work in progress, since server-side prefix filtering is due eventually.
Swift Language Server is totally unusable, it is taking about 10 seconds to type anything. This is not just due to LSC, if anything it feels like a lot more time is spent in the server.
However, Go's language server is blazingly fast. LSC is popping up the completion menu instantly.
Microsoft's TypeScript language server, which can also be used for JavaScript as well, is also quite speedy.
Rust's language server feels slow even though the match list is small.
Performance is a combination of server-side performance and client-side handling. Slow servers exist. Likewise clients in pure VimScript, such as LSC, can be made slow if given too much content as Dart's Analysis Server is currently doing.
Recommendations for LSC
The best language servers are already fast and lean as evidenced by Go and to an extent the TypeScript language servers.
VimScript theoretically will also be getting faster in Vim9:
https://github.com/brammool/vim9/blob/master/README.md
For now, I would wait and see how Dart's upcoming Analysis Server changes impact LSC. If that trims the completion way back then I would be inclined to close the issue.
Another item spawned fro #291
The Dart Analysis Server that ships with Flutter 1.17 is sending upwards of 27,000 completion items to LSC's auto-completion engine.
Needless to say, VimScript and LSC is not handling that well (pauses and stutters whilst in Vim's insert mode).
A future version of the Dart Analysis Server should pare that back greatly via server-side prefix filtering. So it may not be a problem for Dart soon (to-be-determined).
However, the fundamental issue remains, how to deal with Language Servers that send thousands of completion items? Ideally we don't want LSC stuttering and pausing.
Question, does any other mainstream language server send huge completion lists? That is a research topic I will undertake, my plan is to investigate the servers for these languages:
tsserver)If none of the above are bad actors then I would not bother with this, just resolve it.
If some LS do send very large completion lists then it may be worth exploring the possibility of hard capping completions to a reasonable number, say 1,000, and then implementing
IsIncomplete=true-style completion; which would complicate LSC, and the benefits of which may not worth it.For example I wonder if JSON decoding is taking up just as much times as list processing? I don't know.
I hope Dart's huge payload was a once off and that we don't need to think about this.
I will feed back my findings over the next week or so depending on my free time.