Support sending some commands to syntax TS Server while a project is loading

[mjbvz]

Problem

VS Code runs two TS servers for our JavaScript and TypeScript support:

• Syntax Server. Use for basic syntax related operations, such as outline, auto closing tags, etc. Only loads the current file

• Semantic server. Used for more advanced operations such as errors and intellisense. Requires loading the entire project

For larger projects, the semantic server can take time to load the entire project and start providing responses. While the project is loading, the user does not get any IntelliSense.

Here's the state of things today:

Stage	Syntax Operations (Outline)	Semantic Operations (IntelliSense)	Diagnostics
Loading	Full	None	None
Loaded	Full	Full	Full

Proposal

We'd like to explore improving the UX while a project is loading by letting the syntax server handle basic semantic operations until the project has been fully loaded:

Stage	Syntax Operations (Outline)	Semantic Operations (IntelliSense)	Diagnostics
Loading	Full	Partial	None
Loaded	Full	Full	Full

While loading is happening, we plan to use the syntax server to implement semantic operations such as hover and IntelliSense.

The key limitation of this approach is that the syntax server only knows about the current file, so it will not be able to provide complete results. For example, IntelliSense would only include suggestions from the current file and would not be able to support auto imports

[mjbvz]

See microsoft/TypeScript#38564 for the TS work on this

480c98f should enabled this in VS Code (you'll need to wait for the first VS Code 1.47 insiders build). To enable this, just set "typescript.tsserver.useSeparateSyntaxServer": "dynamic". You'll also need to be using a supported TS build

/cc @sheetalkamat @DanielRosenwasser

[DanielRosenwasser]

Nice! (@amcasey)

Just to be clear, it looks like it's not just intellisense/completions, right? It looks like the syntax server will basically handle every operation except for diagnostics:

480c98f#diff-f647ee692cab93fdf6b2650168d3f315R530-R533

[mjbvz]

Yes, during project load syntax server should now get every command except the diagnostic ones and projectInfo. Let me know if there are any other commands I should add to that list

[amcasey]

We probably don't want any of the compile-on-save commands to go to the syntax server.

[amcasey]

Organize imports can only mangle things. Personally, I'd also drop semantic classification (e.g. class vs interface) since I don't think a guess is better than nothing (e.g. just knowing its a type).

[DanielRosenwasser]

I'm not able to see things working better. I've

• installed the latest VS Code Insiders assuming it has commit 480c98f
• set "typescript.tsserver.useSeparateSyntaxServer": "dynamic",
• installed this TypeScript build: Syntax only server creates inferred project with all the open files w… TypeScript#38561 (comment)

[mjbvz]

@DanielRosenwasser You need to be on the VS code 1.47 insiders builds which have not been released yet. They should come out once we ship the stable version of VS Code 1.46

[DanielRosenwasser]

D'oh - thanks! By the way, I (like @amcasey) tried out the syntax-only server and the results are pretty great already. Very excited to see how this works out.