mcp: adopt finalized completions API, support resolved args for prompts too (microsoft#250909)

Refs microsoft#248418

Author: connor4312

src/vs/workbench/contrib/mcp/browser/mcpPromptArgumentPick.ts

@@ -82,7 +82,7 @@ export class McpPromptArgumentPick extends Disposable {
 			quickPick.activeItems = restore?.activeItems ?? [];
 			quickPick.buttons = i > 0 ? [this._quickInputService.backButton] : [];
 
-			const value = await this._getArg(arg, !!restore, token);
+			const value = await this._getArg(arg, !!restore, args, token);
 			if (value.type === 'back') {
 				i -= 2;
 			} else if (value.type === 'cancel') {
@@ -102,15 +102,15 @@ export class McpPromptArgumentPick extends Disposable {
 		return args;
 	}
 
-	private async _getArg(arg: MCP.PromptArgument, didRestoreState: boolean, token?: CancellationToken): Promise<Action> {
+	private async _getArg(arg: MCP.PromptArgument, didRestoreState: boolean, argsSoFar: Record<string, string | undefined>, token?: CancellationToken): Promise<Action> {
 		const { quickPick } = this;
 		const store = new DisposableStore();
 
 		const input$ = observableValue(this, quickPick.value);
 		const asyncPicks = [
 			{
 				name: localize('mcp.arg.suggestions', 'Suggestions'),
-				observer: this._promptCompletions(arg, input$),
+				observer: this._promptCompletions(arg, input$, argsSoFar),
 			},
 			{
 				name: localize('mcp.arg.files', 'Files'),
@@ -218,9 +218,16 @@ export class McpPromptArgumentPick extends Disposable {
 		}
 	}
 
-	private _promptCompletions(arg: MCP.PromptArgument, input: IObservable<string>) {
+	private _promptCompletions(arg: MCP.PromptArgument, input: IObservable<string>, argsSoFar: Record<string, string | undefined>) {
+		const alreadyResolved: Record<string, string> = {};
+		for (const [key, value] of Object.entries(argsSoFar)) {
+			if (value) {
+				alreadyResolved[key] = value;
+			}
+		}
+
 		return this._asyncCompletions(input, async (i, t) => {
-			const items = await this.prompt.complete(arg.name, i, t);
+			const items = await this.prompt.complete(arg.name, i, alreadyResolved, t);
 			return items.map((i): PickItem => ({ id: `suggest:${i}`, label: i, action: 'suggest' }));
 		});
 	}

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

@@ -668,10 +668,11 @@ class McpPrompt implements IMcpPrompt {
 		return result.messages;
 	}
 
-	async complete(argument: string, prefix: string, token?: CancellationToken): Promise<string[]> {
+	async complete(argument: string, prefix: string, alreadyResolved: Record<string, string>, token?: CancellationToken): Promise<string[]> {
 		const result = await McpServer.callOn(this._server, h => h.complete({
 			ref: { type: 'ref/prompt', name: this._definition.name },
-			argument: { name: argument, value: prefix, }
+			argument: { name: argument, value: prefix },
+			context: { arguments: alreadyResolved },
 		}, token), token);
 		return result.completion.values;
 	}
@@ -849,7 +850,9 @@ class McpResourceTemplate implements IMcpResourceTemplate {
 		const result = await McpServer.callOn(this._server, h => h.complete({
 			ref: { type: 'ref/resource', uri: this._definition.uriTemplate },
 			argument: { name: templatePart, value: prefix },
-			resolved: mapValues(alreadyResolved, v => Array.isArray(v) ? v.join('/') : v),
+			context: {
+				arguments: mapValues(alreadyResolved, v => Array.isArray(v) ? v.join('/') : v),
+			},
 		}, token), token);
 		return result.completion.values;
 	}

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

@@ -521,7 +521,7 @@ export class McpServerRequestHandler extends Disposable {
 	/**
 	 * Find completions for an argument
 	 */
-	complete(params: MCP.CompleteRequest2['params'], token?: CancellationToken): Promise<MCP.CompleteResult> {
-		return this.sendRequest<MCP.CompleteRequest2, MCP.CompleteResult>({ method: 'completion/complete', params }, token);
+	complete(params: MCP.CompleteRequest['params'], token?: CancellationToken): Promise<MCP.CompleteResult> {
+		return this.sendRequest<MCP.CompleteRequest, MCP.CompleteResult>({ method: 'completion/complete', params }, token);
 	}
 }

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

@@ -330,7 +330,7 @@ export interface IMcpPrompt {
 	readonly arguments: readonly MCP.PromptArgument[];
 
 	/** Gets string completions for the given prompt part. */
-	complete(argument: string, prefix: string, token: CancellationToken): Promise<string[]>;
+	complete(argument: string, prefix: string, alreadyResolved: Record<string, string>, token: CancellationToken): Promise<string[]>;
 
 	resolve(args: Record<string, string | undefined>, token?: CancellationToken): Promise<IMcpPromptMessage[]>;
 }

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

@@ -14,16 +14,8 @@
  */
 export namespace MCP {
 
-	// https://github.com/modelcontextprotocol/modelcontextprotocol/pull/598
-	export interface CompleteRequest2 extends MCP.CompleteRequest {
-		params: MCP.CompleteRequest['params'] & {
-			/**
-			 * Previously-resolved variables in a URI template. The keys of the object
-			 * are be the template's variable expressions including surrounding braces.
-			 */
-			resolved?: { [key: string]: string };
-		};
-	}
+	// Nothing, yet
+
 }
 
 //#endregion
@@ -1144,6 +1136,16 @@ export namespace MCP {
 				 */
 				value: string;
 			};
+
+			/**
+			 * Additional, optional context for completions
+			 */
+			context?: {
+				/**
+				 * Previously-resolved variables in a URI template or prompt.
+				 */
+				arguments?: { [key: string]: string };
+			};
 		};
 	}