add folder to worskpace can lead to duplicate folders

src/vs/workbench/browser/actions/workspaceCommands.ts

@@ -70,7 +70,7 @@ CommandsRegistry.registerCommand({
 			}
 
 			// Add and show Files Explorer viewlet
-			return workspaceEditingService.addFolders(folders.map(folder => ({ uri: folder })))
+			return workspaceEditingService.addFolders(folders.map(folder => ({ uri: resources.removeTrailingPathSeparator(folder) })))
 				.then(() => viewletService.openViewlet(viewletService.getDefaultViewletId(), true))
 				.then(() => undefined);
 		});

src/vs/workbench/services/workspace/node/workspaceEditingService.ts

@@ -21,7 +21,7 @@ import { BackupFileService } from 'vs/workbench/services/backup/node/backupFileS
 import { ICommandService } from 'vs/platform/commands/common/commands';
 import { distinct } from 'vs/base/common/arrays';
 import { isLinux, isWindows, isMacintosh } from 'vs/base/common/platform';
-import { isEqual, basename, isEqualOrParent } from 'vs/base/common/resources';
+import { isEqual, basename, isEqualOrParent, getComparisonKey } from 'vs/base/common/resources';
 import { INotificationService, Severity } from 'vs/platform/notification/common/notification';
 import { IFileService } from 'vs/platform/files/common/files';
 import { IEnvironmentService } from 'vs/platform/environment/common/environment';
@@ -205,7 +205,7 @@ export class WorkspaceEditingService implements IWorkspaceEditingService {
 		if (state !== WorkbenchState.WORKSPACE) {
 			let newWorkspaceFolders = this.contextService.getWorkspace().folders.map(folder => ({ uri: folder.uri } as IWorkspaceFolderCreationData));
 			newWorkspaceFolders.splice(typeof index === 'number' ? index : newWorkspaceFolders.length, 0, ...foldersToAdd);
-			newWorkspaceFolders = distinct(newWorkspaceFolders, folder => isLinux ? folder.uri.toString() : folder.uri.toString().toLowerCase());
+			newWorkspaceFolders = distinct(newWorkspaceFolders, folder => getComparisonKey(folder.uri));
 
 			if (state === WorkbenchState.EMPTY && newWorkspaceFolders.length === 0 || state === WorkbenchState.FOLDER && newWorkspaceFolders.length === 1) {
 				return Promise.resolve(); // return if the operation is a no-op for the current state