debug: expose parent session on DebugSessions

For https://github.com/microsoft/vscode/issues/123403

src/vs/vscode.proposed.d.ts

@@ -3309,4 +3309,16 @@ declare module 'vscode' {
 	}
 
 	//#endregion
+
+	//#region Expose parent session on DebugSessions - https://github.com/microsoft/vscode/issues/123403#issuecomment-843269200
+
+	export interface DebugSession {
+		/**
+		 * The parent session of this debug session, if it was created as a child.
+		 * @see DebugSessionOptions.parentSession
+		 */
+		readonly parentSession?: DebugSession;
+	}
+
+	//#endregion
 }

src/vs/workbench/api/browser/mainThreadDebugService.ts

@@ -329,7 +329,8 @@ export class MainThreadDebugService implements MainThreadDebugServiceShape, IDeb
 					type: session.configuration.type,
 					name: session.name,
 					folderUri: session.root ? session.root.uri : undefined,
-					configuration: session.configuration
+					configuration: session.configuration,
+					parent: session.parentSession?.getId(),
 				};
 			}
 		}

src/vs/workbench/api/common/extHost.protocol.ts

@@ -1780,6 +1780,7 @@ export interface IDebugSessionFullDto {
 	id: DebugSessionUUID;
 	type: string;
 	name: string;
+	parent: DebugSessionUUID | undefined;
 	folderUri: UriComponents | undefined;
 	configuration: IConfig;
 }

src/vs/workbench/api/common/extHostDebugService.ts

@@ -845,7 +845,8 @@ export abstract class ExtHostDebugServiceBase implements IExtHostDebugService, E
 				let ds = this._debugSessions.get(dto.id);
 				if (!ds) {
 					const folder = await this.getFolder(dto.folderUri);
-					ds = new ExtHostDebugSession(this._debugServiceProxy, dto.id, dto.type, dto.name, folder, dto.configuration);
+					const parent = dto.parent ? this._debugSessions.get(dto.parent) : undefined;
+					ds = new ExtHostDebugSession(this._debugServiceProxy, dto.id, dto.type, dto.name, folder, dto.configuration, parent);
 					this._debugSessions.set(ds.id, ds);
 					this._debugServiceProxy.$sessionCached(ds.id);
 				}
@@ -872,7 +873,8 @@ export class ExtHostDebugSession implements vscode.DebugSession {
 		private _type: string,
 		private _name: string,
 		private _workspaceFolder: vscode.WorkspaceFolder | undefined,
-		private _configuration: vscode.DebugConfiguration) {
+		private _configuration: vscode.DebugConfiguration,
+		private _parentSession: vscode.DebugSession | undefined) {
 	}
 
 	public get id(): string {
@@ -886,12 +888,15 @@ export class ExtHostDebugSession implements vscode.DebugSession {
 	public get name(): string {
 		return this._name;
 	}
-
 	public set name(name: string) {
 		this._name = name;
 		this._debugServiceProxy.$setDebugSessionName(this._id, name);
 	}
 
+	public get parentSession(): vscode.DebugSession | undefined {
+		return this._parentSession;
+	}
+
 	_acceptNameChanged(name: string) {
 		this._name = name;
 	}