Language Server (onion-lsp)

The Onion Language Server provides IDE features for .on files. It is used by the VSCode extension (vscode-onion/) and can be integrated with any editor that supports the Language Server Protocol.

Starting the server

onion-lsp

The server communicates over stdin/stdout using LSP.

Supported features

Feature	Description
Syntax diagnostics	Compilation errors reported as you type
Hover	Documentation for keywords, built-in types, and user-defined symbols
Go to definition	Jump to the definition of a user-defined symbol
Code completion	Keywords, built-ins, modules, and user-defined symbols
Document symbols	Outline view of classes, interfaces, methods, enums, records, and fields
Workspace symbols	Search symbols across all open documents
Signature help	Method signatures while typing a call
Rename symbol	Rename occurrences of the symbol at the cursor in the current file

Symbol support

The language server indexes the following symbols from open documents:

• Classes, interfaces, enums, and records
• Methods (def)
• Class-level fields (val / var)
• Method arguments and local variables

Symbol information is used for completion, hover, go-to-definition, and both document and workspace symbol requests.

VSCode integration

Install the vscode-onion extension. It will automatically start onion-lsp when you open an .on file and connect it to the editor.