commentProvider can control collapse state of a thread

src/vs/workbench/api/node/extHost.api.impl.ts

@@ -686,7 +686,9 @@ export function createApiFactory(
 			FileType: extHostTypes.FileType,
 			FoldingRangeList: extHostTypes.FoldingRangeList,
 			FoldingRange: extHostTypes.FoldingRange,
-			FoldingRangeType: extHostTypes.FoldingRangeType
+			FoldingRangeType: extHostTypes.FoldingRangeType,
+
+			CommentThreadCollapsibleState: extHostTypes.CommentThreadCollapsibleState
 		};
 	};
 }

src/vs/workbench/api/node/extHostComments.ts

@@ -103,6 +103,7 @@ function convertCommentThread(vscodeCommentThread: vscode.CommentThread, command
 		resource: vscodeCommentThread.resource.toString(),
 		range: extHostTypeConverter.fromRange(vscodeCommentThread.range),
 		comments: vscodeCommentThread.comments.map(convertComment),
+		collapsibleState: vscodeCommentThread.collapsibleState,
 		reply: vscodeCommentThread.reply ? commandsConverter.toInternal(vscodeCommentThread.reply) : null
 	};
 }

src/vs/workbench/api/node/extHostTypes.ts

@@ -1868,3 +1868,15 @@ export enum FoldingRangeType {
 }
 
 //#endregion
+
+
+export enum CommentThreadCollapsibleState {
+	/**
+	 * Determines an item is collapsed
+	 */
+	Collapsed = 0,
+	/**
+	 * Determines an item is expanded
+	 */
+	Expanded = 1
+}