Andrew Branch @andrewbran.ch · 15/08/2026What’s next? Content mappers, I hope! github.com/microsoft/ty... 160
Andrew Branch @andrewbran.ch · 15/08/2026This simple example is running in the extension host, but you can imagine passing this connection to your own LSP server, serving additional completions or hovers in TS files by combining its own logic with type checker queries. 150
Andrew Branch @andrewbran.ch · 15/08/2026Let's do something totally different. Here's a VS Code extension, which gets a sidecar API connection to the TypeScript LSP that was already running. All the same APIs are available, and now you can inspect the projects the user has open in their editor. Here we're logging the exports of .ts files. 150
Andrew Branch @andrewbran.ch · 15/08/2026So far, almost all of this code could be mistaken for the old TS 6 API. But under the hood, a lot of care has to go into pretty silly things like making sure when you get the same Type or Symbol twice, they have reference equality. That doesn't come for free anymore. 140
Andrew Branch @andrewbran.ch · 15/08/2026Now for some transformation. The new AST is a hybrid of these "remote nodes" backed by binary data and normal JavaScript objects. The client can encode the result into the same binary format so the server can run it through the emitter, in this case. Here's a (dumb) codemod to fix our error. 140
Andrew Branch @andrewbran.ch · 15/08/2026To demonstrate the laziness of file decoding, we can see that after recursively visiting one of the two statements in the file, 10 of the 20 nodes were actually materialized. (The timings here look slower than they should because the VFS is not yet production quality.) 150
Andrew Branch @andrewbran.ch · 15/08/2026Every node materializes into an instance of the same class, all reading the same underlying buffer. The TS types lie and give each node a specialized type. Here, we see `kind` reading its value from an offset computed by the node's index in the flattened AST and the kind field's offset. 260
Andrew Branch @andrewbran.ch · 15/08/2026But how exactly does that work? The tsgo process encodes the AST in a compact binary format and sends it all over. The client's SourceFile type wraps the Uint8Array and exposes getters for every property you could want to access. Children and other properties are lazily decoded on first access. 1110
Andrew Branch @andrewbran.ch · 15/08/2026Slightly more interesting: let's navigate a source file and use the type checker on some stuff. This found the return type 'void' from `console.log` and the return type 'number' from `add`. 1110
Andrew Branch @andrewbran.ch · 15/08/2026Let’s start with something basic like getting diagnostics. Not too much to say about this. Each API call like this is communicating over STDIO with the tsgo process. We'll see some details in a minute. 1181
Andrew Branch @andrewbran.ch · 15/08/2026The API comes in sync and async flavors. You import from "unstable" for now, but it's not going to change architecturally before 7.1. Breaks will be mostly targeted renames/moves. You access programs through obtaining immutable snapshots. There will be more ways coming soon. More on this later. 1161
Andrew Branch @andrewbran.ch · 15/08/2026If you’re not stalking TypeScript PRs, you might be surprised how much you can do with the API in nightlies (and even in 7.0 stable), so here’s a tiny demo that I think hits some of the highlights. 🧵 412620
