Git: Fix worktree checkout default actions (microsoft#262414)

* fix worktree checkout default action

* remove comments

* clean up

* fix returns

* change action to 'cancel'

Author: nguyenchristy

extensions/git/src/commands.ts

@@ -2938,7 +2938,25 @@ export class CommandCenter {
 				}
 
 				if (err.gitErrorCode === GitErrorCodes.WorktreeBranchAlreadyUsed) {
-					this.handleWorktreeBranchAlreadyUsed(err);
+					// Not checking out in a worktree (use standard error handling)
+					if (!repository.dotGit.commonPath) {
+						await this.handleWorktreeBranchAlreadyUsed(err);
+						return false;
+					}
+
+					// Check out in a worktree (check if worktree's main repository is open in workspace and if branch is already checked out in main repository)
+					const commonPath = path.dirname(repository.dotGit.commonPath);
+					if (workspace.workspaceFolders && workspace.workspaceFolders.some(folder => pathEquals(folder.uri.fsPath, commonPath))) {
+						const mainRepository = this.model.getRepository(commonPath);
+						if (mainRepository && item.refName && item.refName.replace(`${item.refRemote}/`, '') === mainRepository.HEAD?.name) {
+							const message = l10n.t('Branch "{0}" is already checked out in the current window.', item.refName);
+							await window.showErrorMessage(message, { modal: true });
+							return false;
+						}
+					}
+
+					// Check out in a worktree, (branch is already checked out in existing worktree)
+					await this.handleWorktreeBranchAlreadyUsed(err);
 					return false;
 				}
 
@@ -3744,7 +3762,6 @@ export class CommandCenter {
 		return;
 	}
 
-
 	@command('git.deleteWorktree', { repository: true, repositoryFilter: ['worktree'] })
 	async deleteWorktree(repository: Repository): Promise<void> {
 		if (!repository.dotGit.commonPath) {