When 'got rebase' is successful, the worktree is switched to the
rebased branch.  However, when there are no commits on the current
branch to rebase, got will error and worktree is left unmodified.
More than once I have not paid attention to the error message (instead
treating it more as information), and assumed that the branch was
switched, only to end up committing later changes to origin/main
instead of main.

Since a noop rebase could also be seen as successful rebase operation,
we could switch the branch as well, and exit with code 0 instead of 1.
If my memory serves me right, git rebase also behaves similarly when
there is no commits to rebase.

diff a9e66726ec8e6d4997a024f572ee53719f7b9cdb /home/jrick/src/got
blob - 488cd9f35722bed936af6e7d9e2c6aa77ea2a3d8
file + got/got.c
--- got/got.c
+++ got/got.c
@@ -9147,12 +9147,16 @@ cmd_rebase(int argc, char *argv[])
 				goto done;
 			error = NULL;
 		} else {
-			static char msg[128];
-			snprintf(msg, sizeof(msg),
-			    "%s is already based on %s",
+			printf("%s is already based on %s\n",
 			    got_ref_get_name(branch),
 			    got_worktree_get_head_ref_name(worktree));
-			error = got_error_msg(GOT_ERR_SAME_BRANCH, msg);
+			error = switch_head_ref(branch, branch_head_commit_id,
+			    worktree, repo);
+			if (error)
+				goto done;
+			error = got_worktree_checkout_files(worktree,
+			    &merged_paths, repo, update_progress, &upa,
+			    check_cancelled, NULL);
 			goto done;
 		}
 		error = got_worktree_rebase_prepare(&new_base_branch,
blob - b17666eaf0ae899543adfa66236bdfd3eb49e92d
file + regress/cmdline/rebase.sh
--- regress/cmdline/rebase.sh
+++ regress/cmdline/rebase.sh
@@ -247,7 +247,10 @@ test_rebase_ancestry_check() {
 	(cd $testroot/wt && got rebase newbranch > $testroot/stdout \
 		2> $testroot/stderr)
 
-	echo -n > $testroot/stdout.expected
+	echo "refs/heads/newbranch is already based on refs/heads/master" \
+		> $testroot/stdout.expected
+	echo "Switching work tree from refs/heads/master to refs/heads/newbranch" \
+		>> $testroot/stdout.expected
 	cmp -s $testroot/stdout.expected $testroot/stdout
 	ret="$?"
 	if [ "$ret" != "0" ]; then
@@ -256,8 +259,7 @@ test_rebase_ancestry_check() {
 		return 1
 	fi
 
-	echo "got: refs/heads/newbranch is already based on refs/heads/master" \
-		> $testroot/stderr.expected
+	echo -n > $testroot/stderr.expected
 	cmp -s $testroot/stderr.expected $testroot/stderr
 	ret="$?"
 	if [ "$ret" != "0" ]; then