Kestrel

Kestrel LSP

The language server (kestrel-lsp) implements the standard LSP protocol. Anything it offers, your editor will surface — the exact UI depends on the editor. For the install, see Getting Started → Install the LSP Extension.

What the server provides

  • Diagnostics. Errors and warnings as you type, with E-codes that link to Reference → Diagnostics.
  • Completion. Names in scope, member access (obj.), and module paths (std.io.). Completions are HIR-driven, so they reflect what would actually compile, not just what's lexically near.
  • Hover. Type signatures, doc comments, and the resolved type of any expression.
  • Jump-to-definition. Works across modules, including stdlib and dependencies.
  • Find-references. All call sites for a function, all reads of a field, all conformances of a protocol.
  • Rename. Symbol-aware. Renames the declaration and every reference.
  • Document symbols. The outline pane in your editor.
  • Semantic tokens. Better syntax highlighting than a regex-based grammar — the server tells the editor exactly what each token resolves to.
  • Signature help. Inline parameter hints when you're typing a call.
  • Code lens. Inline run/test/debug actions next to functions and tests.

Configuration

The server reads kestrel-lsp.toml from the project root if present:

[diagnostics] unused-binding = "warn" # off | warn | error [completion] include-stdlib = true auto-import = true

Most users don't need to configure anything. The defaults are tuned for typical projects.

Performance

The server is incremental — edits trigger only the analysis affected by the change, not a full re-typecheck. Large projects (thousands of files) stay responsive because the dependency graph is tracked at the symbol level.

Troubleshooting

  • No completions, no diagnostics: the server isn't reaching the project. Check that flock.toml exists at the root and kestrel-lsp is on your PATH.
  • Stale diagnostics: the file system watcher missed an event. Reload the file or restart the LSP from your editor's command palette.
  • High CPU: usually means an analysis loop. Capture the issue with KESTREL_LSP_LOG=trace and file a bug.