ty_server

ty's Language Server Protocol implementation. Source: crates/ty_server/.

Purpose

Expose ty's type checker as an LSP so editors can show type errors, hover types, completions, go-to-definition, references, and renames in real time.

Directory layout

crates/ty_server/src/
├── lib.rs
├── server/        # request/notification handlers
├── session/       # workspace + project state
├── document/      # in-memory document model
├── capabilities.rs
├── db.rs          # ProjectDatabase wrapper for the LSP
├── system.rs      # System impl that prefers in-memory buffers
└── logging.rs

The binary entry is ty server, defined in crates/ty/src/main.rs.

Why Salsa matters here

Unlike ruff_server, ty's server is built on top of Salsa via ProjectDatabase. Each text-document edit invalidates only the inputs that changed; downstream queries (type inference, scope graph, diagnostic accumulation) are recomputed only where necessary.

This is why the rule "any function touching .node() must be #[salsa::tracked]" matters in practice: forgetting it means the LSP returns stale results after an edit.

Capabilities

ty's server advertises:

• Diagnostics
• Hover (type information)
• Go-to definition / declaration / type-definition
• Find references
• Rename (single-file and cross-file where unambiguous)
• Completion (string-literal-aware where applicable)
• Inlay hints (subset)
• Document symbols

The IDE-specific queries live in ty_ide. ty_server mostly translates LSP requests into ty_ide / ty_python_semantic calls.

How a didChange is processed

sequenceDiagram
    Editor->>Server: textDocument/didChange
    Server->>Session: update buffer + bump revision
    Server->>Db: invalidate file inputs
    Editor->>Server: textDocument/hover
    Server->>Db: salsa query (cached or recomputed)
    Db-->>Server: type info
    Server->>Editor: hover response

Integration points

• Consumes ty_python_semantic, ty_project, ty_ide, ruff_db.
• Speaks LSP via tower-lsp.
• Shipped inside the ty binary.

Modifying

• New LSP feature: usually means adding a tracked query in ty_ide (or ty_python_semantic), then a handler in server/. Update capabilities.rs to advertise.
• Editor-specific quirks: keep workarounds in server/ and document why.
• Add a test in crates/ty_server/tests/ for every behavior change.

For Ruff's LSP, see ruff_server. For the user-facing perspective, see LSP servers.