LSP 3.17 remains the current spec, and Rust can extend it with custom JSON-RPC methods, diagnostics, and hover support for DSLs in editors. Read now.
Why DSLs Need More Than a Grammar
A domain-specific language earns its keep by expressing one problem well, but editor tooling rarely follows automatically. Syntax highlighting from a TextMate grammar gives you color, not understanding. To catch an undefined reference, explain a symbol on hover, or flag a rule violation as you type, the editor needs a running program that understands your language's semantics. The Language Server Protocol is the contract that lets one such program serve every LSP-aware editor instead of writing a plugin per editor.
LSP 3.17 remains the current spec, and it covers the common ground: diagnostics, hover, completion, go-to-definition, and more. For a DSL, the interesting work is deciding which of these standard requests map cleanly onto your language and where you need to reach past the spec with your own methods.
Building the Server in Rust
Rust is a comfortable fit for a language server because the work is exactly what it's good at: parsing text into a syntax tree, walking that tree, and doing it fast enough to respond on every keystroke. The ecosystem gives you async runtimes and JSON-RPC plumbing so you can focus on the analysis rather than the transport. A server reads requests over stdio or a socket, keeps an in-memory model of each open document, and answers requests against that model.
A practical loop for a DSL server looks like this:
- Parse each document into a tree, keeping byte or line/column spans so you can map back to editor positions.
- Build a symbol table or scope model that resolves references across the file.
- Re-run the relevant analysis when a document changes, ideally incrementally rather than from scratch.
- Translate your internal findings into LSP payloads with accurate ranges.
Extending Beyond the Standard Methods
The standard requests handle a lot, but a DSL often has concepts the spec never anticipated: evaluating an expression, listing every place a config key is used, or triggering a domain-specific transformation. Because LSP is JSON-RPC underneath, you can register custom methods with your own namespaced names and have the editor call them. The client sends a request, your Rust server dispatches on the method string, and you return a structured result. This keeps DSL-specific behavior out of the standard channels, where it might confuse other tooling, while still riding the same connection.
Diagnostics and hover are usually the highest-value features to implement first. Diagnostics turn your validation rules into inline squiggles with messages and severities, so authors see mistakes without running anything. Hover lets you attach a plain-language explanation or resolved value to a symbol, which is often the fastest way to make an unfamiliar DSL learnable.
Keeping It Robust and Fast
A language server runs continuously and must survive malformed input, since users spend most of their time typing incomplete code. Favor a parser that recovers from errors and produces a usable tree even when the document doesn't fully parse; returning partial results beats returning nothing. Guard against panics in request handlers so one bad document doesn't take down the session.
Latency is felt directly because responses gate the editor's feedback. Cache parsed trees per document, do incremental updates on change events, and avoid recomputing analysis you already have. Test the server against real editor traffic early: the difference between a server that works on a saved file and one that works mid-keystroke is where most of the effort actually goes.