Based on the starter code at https://code.visualstudio.com/api/language-extensions/language-server-extension-guide

This Language Server registers and works for .tl files. It has the following language features so far:

• Completions based on the Tealish langspec AND the TEAL v7 langspec.json file
• Diagnostics are still TBD but framed up in the language server

It also includes an End-to-End test from the template which will need to get much more specific to Tealish syntax, etc

.
├── client // Language Client
│   ├── src
│   │   ├── test // End to End tests for Language Client / Server
│   │   └── extension.ts // Language Client entry point
├── package.json // The extension manifest.
└── server // Language Server
    └── src
        └── server.ts // Language Server entry point

• Run npm install in this folder. This installs all necessary npm modules in both the client and server folder
• Open VS Code on this folder.
• Press Ctrl+Shift+B to start compiling the client and server
• Switch to the Run and Debug View in the Sidebar (Ctrl+Shift+D).
• Select Launch Client from the drop down (if it is not already).
• Press ▷ to run the launch config (F5).
• If you want to debug the server as well, use the launch configuration Attach to Server
• In the Extension Development Host instance of VSCode, open a document in 'tealish' language mode (a .tl file should open in this mode already)
• Type Txn or Global or any other Tealish operator to see completions based on the tealish langspec. Try any other TEAL opcode to see the server's compeltion and docs from langspec.json.