Language Server Protocol (LSP)

Quick Start

import { createConnection, TextDocuments, ProposedFeatures } from 'vscode-languageserver/node';
import { TextDocument } from 'vscode-languageserver-textdocument';

const connection = createConnection(ProposedFeatures.all);
const documents = new TextDocuments(TextDocument);

connection.onInitialize((params) => ({
  capabilities: {
    textDocumentSync: TextDocumentSyncKind.Incremental,
    completionProvider: { resolveProvider: true },
    hoverProvider: true,
    definitionProvider: true,
    diagnosticProvider: { interFileDependencies: false, workspaceDiagnostics: false }
  }
}));

documents.onDidChangeContent((change) => {
  validateDocument(change.document);
});

documents.listen(connection);
connection.listen();

Core Concepts

• Connection: JSON-RPC communication channel between client and server
• TextDocuments: Manages open document state with incremental sync
• Capabilities: Server declares features in onInitialize response
• Diagnostics: Errors/warnings pushed via connection.sendDiagnostics()

Common Providers

Key Patterns

• Use TextDocument.positionAt(offset) and offsetAt(position) for conversions
• Return null from handlers when no result available
• Diagnostics use DiagnosticSeverity.Error | Warning | Information | Hint
• Use Location for definitions, LocationLink for richer go-to-definition