Fixes missing onDidChangeSemanticTokens event support in DocumentRangeSemanticTokensProvider to provide API parity with DocumentSemanticTokensProvider.

Problem

The DocumentRangeSemanticTokensProvider interface lacked the onDidChangeSemanticTokens event that is available in DocumentSemanticTokensProvider. This prevented extensions from notifying VS Code when range-specific semantic tokens needed to be refreshed, forcing unnecessary re-computation and limiting performance optimizations.

This was originally reported against the Language Server Protocol via the C# team (microsoft/vscode-languageserver-node#1672).

Solution

Added optional onDidChangeSemanticTokens?: Event<void> property to DocumentRangeSemanticTokensProvider following the same pattern as the document provider:

export interface DocumentRangeSemanticTokensProvider {
	onDidChange?: Event<void>;  // New optional event
	getLegend(): SemanticTokensLegend;
	provideDocumentRangeSemanticTokens(model: ITextModel, range: Range, token: CancellationToken): ProviderResult<SemanticTokens>;
}

Implementation

• Interface: Added optional onDidChange event property to maintain backward compatibility
• Main Thread: Updated MainThreadDocumentRangeSemanticTokensProvider to accept and handle event emitters
• Registration: Enhanced registration logic to support optional event subscriptions with proper cleanup
• Protocol: Added $emitDocumentRangeSemanticTokensEvent method for cross-process communication
• Extension Host: Updated registration to forward events from extensions to main thread
• API: Updated VS Code extension API definition to expose the new capability

Usage

Extensions can now implement event-driven semantic token refreshing:

class MyRangeProvider implements vscode.DocumentRangeSemanticTokensProvider {
	private _onDidChangeSemanticTokens = new vscode.EventEmitter<void>();
	readonly onDidChangeSemanticTokens = this._onDidChangeSemanticTokens.event;

	constructor() {
		// Refresh tokens when configuration changes
		vscode.workspace.onDidChangeConfiguration(() => {
			this._onDidChangeSemanticTokens.fire();
		});
	}

	provideDocumentRangeSemanticTokens(document, range, token) {
		// Implementation here
	}
}

Testing

Added comprehensive tests verifying both scenarios:

• Providers with onDidChangeSemanticTokens event work correctly
• Providers without the event continue to work (backward compatibility)

The changes are fully backward compatible - existing range semantic token providers continue to work unchanged, while new providers can opt into event-driven refreshing for better performance.

Fixes #268140

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.