Asynchronously show completion items from different sources or extensions!

[HaoboGu]

Currently, completion items from different sources/extension are shown in a synchronous way, which means the result won't be shown before the last completionProvider completes. There are a lot of great auto-complete extensions in the marketplace, some of them can be quite efficient, but the overall completion latency still depends on the slowest extension, which is I think is not reasonable. So I propose to add an asynchronously way to show the completion list from different extensions or sources, just like IDEA:

In VSCode:

Here I added a delay manually in my own extension, but as you can see, the results come from vscode-java extension are also affected, which results in bad user experience.

Please consider this, thank you!

[jrieken]

Yeah, this isn't the first time this issue comes up and not the only place where is comes up, e.g there are related discussions around reference search results. These are the challenges which need good ideas:

1. When showing results as they come you will always see snippets and word-based suggestions first. Those are computed in the renderer or in a separate worker and are always very fast. So, you will always see results first that are of lower quality.
2. We have logic to make "better" providers mute results from other providers. E.g a provider that is registered specifically for that language overwrites results from a provider that is registered for all languages (using the * document selector). We do this to hide word-based suggestions in the presence of "good" suggestions (tho not everyone likes this). However, this logic requires all providers to have finished.
3. Sorting/ranking is an issue. Image you have the Foo-prefix and quickly get a suggestion that is barFangBoo. A split second later comes another suggestion which is FooBar. This suggestion should be ranked higher which means the widget needs to be re-sorted while it is showing. That can be very problematic and confusing to users. Image in that moment you wanted to select the "barFangBoo" suggestion. So either you resort of the cost of confusion or you simply append at the cost of not showing the best suggestions atop (which is amplified given that "simple" providers are likely to be faster)

[HaoboGu]

Hello jrieken, thanks for your reply!

1. It's great to have word-base suggestion in plaintext files. But in general code files, the word-base suggestion won't help a lot. So I think word-base suggestion can be disabled if there exists other completion providers, not just be overwritten.

2. If the lower quality suggestion is disabled, the overwriting mechanism is no longer necessary.

3. This is the core issue IMO. I did some tests on IDEA intellij, there are some interesting tricks I observed:
   1). The first 5 results will never be resorted/overwritten
   2). Snippet results do appear on the top of the list sometimes. However, if I don't choose them, they will be filtered when I keep typing new characters and other better results come to top
   3). All resorting/reranking operations have a time-out, after that, no resorting/reranking will be performed. In the current version of IDEA, this time-out seems to be 200ms-300ms. So for me, the reranking is done before I can check all the results. It isn't confusing me at all
   4). The reranking will be triggered again when I keep typing with filtering old items

So how about setting a hard time-out for reranking to prevent confusing users? In this case rank score of completionItems might invalid, but I think it's acceptable. Because the order can be fixed if the user chooses to keep typing.

[jrieken]

So I think word-base suggestion can be disabled if there exists other completion providers, not just be overwritten.

That's a bold assumption which isn't generally true. There are many cases in which word-based suggestions make sense - despite having a smart completion provider. E.g typing inside comments, typing inside string, cases in which the smart provider has issues/bugs.

[HaoboGu]

There are many cases in which word-based suggestions make sense - despite having a smart completion provider. E.g typing inside comments, typing inside string, cases in which the smart provider has issues/bugs.

As far as I know, the word-base suggestion is disabled by default in code files right now. I just tested it, even though When I was typing inside string or comment, it wasn't triggered.

Actually, according to my experience, I don't see any inconvenience in other IDEs which don't have word-base suggestions.

If we cannot just simply disable the word-based suggestion, why don't we just take advantage of asynchronous ability?

We don't have to wait all completion providers, word-base suggestions are hided if there exists completion items come from other providers or when the first other asynchronous result comes. If better results are really really late, rerank the completion list and put word-base completion at the bottom if the user continues to type.

[jrieken]

You might have word based completions disabled. Again, we will not have a discussion about the removal of word-based completions. This is not an option!

[HaoboGu]

Yeah, OK.
I am wondering can the overwriting logic you mentioned above be migrated to an asynchronous way?

The main problem of introducing asynchronous suggestion is how do we update completion list. Combining a hard time-out and reranking when the user continues to type is a feasible way IMO. How do you think about this plan?

[jrieken]

The simplest would be this

1. Always wait for the first non-simple provider (non word-based, non snippet)
2. Then update the list as more results come in
3. Don't resort when more results come in
4. Resort when more prefix text is typed

[HaoboGu]

2. Then update the list as more results come in

Does 'update' mean appending results at the bottom of the list?

[jrieken]

yes

[HaoboGu]

This looks good to me!

[HaoboGu]

Any plan on this issue?