Fix microsoft#143881

Author: Jackson Kearl

src/vs/workbench/contrib/files/browser/views/explorerView.ts

@@ -58,6 +58,7 @@ import { IEditorResolverService } from 'vs/workbench/services/editor/common/edit
 import { IPaneCompositePartService } from 'vs/workbench/services/panecomposite/browser/panecomposite';
 import { INotificationService } from 'vs/platform/notification/common/notification';
 import { EditorOpenSource } from 'vs/platform/editor/common/editor';
+import { ResourceMap } from 'vs/base/common/map';
 
 interface IExplorerViewColors extends IColorMapping {
 	listDropBackground?: ColorValue | undefined;
@@ -691,13 +692,31 @@ export class ExplorerView extends ViewPane implements IExplorerView {
 				if (!previousInput && input.length === 1 && this.configurationService.getValue<IFilesConfiguration>().explorer.expandSingleFolderWorkspaces) {
 					await this.tree.expand(input[0]).catch(() => { });
 				}
-				if (Array.isArray(previousInput) && previousInput.length < input.length) {
-					// Roots added to the explorer -> expand them.
-					await Promise.all(input.slice(previousInput.length).map(async item => {
-						try {
-							await this.tree.expand(item);
-						} catch (e) { }
-					}));
+				// TODO@jkearl: Hidden & Probably not needed, remove eventaully.
+				const useOldStyle = this.configurationService.getValue<boolean>('explorer.legacyWorkspaceFolderExpandMode');
+				if (useOldStyle) {
+					if (Array.isArray(previousInput) && previousInput.length < input.length) {
+						// Roots added to the explorer -> expand them.
+						await Promise.all(input.slice(previousInput.length).map(async item => {
+							try {
+								await this.tree.expand(item);
+							} catch (e) { }
+						}));
+					}
+				} else {
+					if (Array.isArray(previousInput)) {
+						const previousRoots = new ResourceMap<true>();
+						previousInput.forEach(previousRoot => previousRoots.set(previousRoot.resource, true));
+
+						// Roots added to the explorer -> expand them.
+						await Promise.all(input.map(async item => {
+							if (!previousRoots.has(item.resource)) {
+								try {
+									await this.tree.expand(item);
+								} catch (e) { }
+							}
+						}));
+					}
 				}
 			}
 			if (initialInputSetup) {