mcp: forward log level changes to MCP servers

Fixes microsoft#256267

* Initial plan

* Implement MCP server log level forwarding

Co-authored-by: connor4312 <[email protected]>

* Add tests for MCP server log level functionality

Co-authored-by: connor4312 <[email protected]>

* Move log level forwarding to McpServerRequestHandler and clean up imports

Co-authored-by: connor4312 <[email protected]>

* properly

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: connor4312 <[email protected]>
Co-authored-by: Connor Peet <[email protected]>

Author: Copilot

src/vs/workbench/contrib/mcp/common/mcpServerRequestHandler.ts

@@ -4,6 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { equals } from '../../../../base/common/arrays.js';
+import { assertNever } from '../../../../base/common/assert.js';
 import { DeferredPromise, IntervalTimer } from '../../../../base/common/async.js';
 import { CancellationToken } from '../../../../base/common/cancellation.js';
 import { CancellationError } from '../../../../base/common/errors.js';
@@ -122,6 +123,7 @@ export class McpServerRequestHandler extends Disposable {
 				}, token);
 
 				mcp._serverInit = initialized;
+				mcp._sendLogLevelToServer(opts.logger.getLevel());
 
 				mcp.sendNotification<MCP.InitializedNotification>({
 					method: 'notifications/initialized'
@@ -166,6 +168,11 @@ export class McpServerRequestHandler extends Disposable {
 				this.cancelAllRequests();
 			}
 		}));
+
+		// Listen for log level changes and forward them to the MCP server
+		this._register(logger.onDidChangeLogLevel((logLevel) => {
+			this._sendLogLevelToServer(logLevel);
+		}));
 	}
 
 	/**
@@ -440,6 +447,22 @@ export class McpServerRequestHandler extends Disposable {
 		super.dispose();
 	}
 
+	/**
+	 * Forwards log level changes to the MCP server if it supports logging
+	 */
+	private async _sendLogLevelToServer(logLevel: LogLevel): Promise<void> {
+		try {
+			// Only send if the server supports logging capabilities
+			if (!this.capabilities.logging) {
+				return;
+			}
+
+			await this.setLevel({ level: mapLogLevelToMcp(logLevel) });
+		} catch (error) {
+			this.logger.error(`Failed to set MCP server log level: ${error}`);
+		}
+	}
+
 	/**
 	 * Send an initialize request
 	 */
@@ -531,3 +554,26 @@ export class McpServerRequestHandler extends Disposable {
 		return this.sendRequest<MCP.CompleteRequest, MCP.CompleteResult>({ method: 'completion/complete', params }, token);
 	}
 }
+
+
+/**
+ * Maps VSCode LogLevel to MCP LoggingLevel
+ */
+function mapLogLevelToMcp(logLevel: LogLevel): MCP.LoggingLevel {
+	switch (logLevel) {
+		case LogLevel.Trace:
+			return 'debug'; // MCP doesn't have trace, use debug
+		case LogLevel.Debug:
+			return 'debug';
+		case LogLevel.Info:
+			return 'info';
+		case LogLevel.Warning:
+			return 'warning';
+		case LogLevel.Error:
+			return 'error';
+		case LogLevel.Off:
+			return 'emergency'; // MCP doesn't have off, use emergency
+		default:
+			return assertNever(logLevel); // Off and other levels are not supported
+	}
+}

src/vs/workbench/contrib/mcp/test/common/mcpServerConnection.test.ts

@@ -21,6 +21,7 @@ import { McpServerConnection } from '../../common/mcpServerConnection.js';
 import { McpCollectionDefinition, McpConnectionState, McpServerDefinition, McpServerTransportType } from '../../common/mcpTypes.js';
 import { TestMcpMessageTransport } from './mcpRegistryTypes.js';
 import { ConfigurationTarget } from '../../../../../platform/configuration/common/configuration.js';
+import { Event } from '../../../../../base/common/event.js';
 
 class TestMcpHostDelegate extends Disposable implements IMcpHostDelegate {
 	private readonly _transport: TestMcpMessageTransport;
@@ -288,6 +289,7 @@ suite('Workbench - MCP - ServerConnection', () => {
 			delegate,
 			serverDefinition.launch,
 			{
+				onDidChangeLogLevel: Event.None,
 				getLevel: () => LogLevel.Debug,
 				info: (message: string) => {
 					loggedMessages.push(message);