Architecture

noyalib-lsp is a Language Server Protocol implementation for YAML, built on noyalib’s parser, CST formatter, and error locations. The transport is stdio with the standard Content-Length framing.

Layers

• src/main.rs is the transport shim: it frames messages and drives Server::handle_message. All behaviour lives in the library so cargo test covers it without an editor.
• src/lib.rs holds Server, which owns the document store of open buffers, and handle_message, which parses the JSON-RPC envelope, routes by method, and returns a HandleOutcome of one of three kinds: reply (a response), notify (a server-initiated notification such as diagnostics), or silent. The capability set advertised at initialize is fixed: textDocumentSync (full), textDocument/formatting, and textDocument/hover, with textDocument/publishDiagnostics pushed after each change.
• src/diagnostics.rs turns noyalib parse errors into LSP diagnostic objects (collect) and wraps them in the publishDiagnostics notification (publish_diagnostics).
• src/format.rs implements formatting as a single TextEdit replacing the whole document with noyalib’s CST formatter output (full_document_edits). One edit keeps the response self-contained; the client needs no cross-document reasoning to apply it.
• src/hover.rs answers textDocument/hover (hover_at): a small Markdown card with the position and the document’s overall type when the buffer parses, or the parse error at the cursor when it does not. byte_offset_of maps an LSP line and column to a byte offset. Schema-driven hover descriptions are tracked as future work.

Data flow

Editor sends didOpen or didChange with the full text; the server stores it, parses it, and pushes diagnostics. Formatting and hover read the stored text on request. Nothing is written to disk.

Testing

Unit tests drive Server::handle_message with raw JSON-RPC strings. Two libFuzzer targets feed it arbitrary messages (fuzz_handle_message) and arbitrary document text through didChange (fuzz_did_change); CI replays the seed corpus on every push. docs/protocol-coverage.md lists which LSP methods are implemented.

Lockstep

The crate pins noyalib at the identical =0.0.X and releases with it (core ADR-0005).