Fix rm failing on in-sync worktree

internal/timber/remove_test.go

@@ -123,6 +123,17 @@ func TestRemoveWithNoArgsFromSubdirectoryRemovesCurrentWorktree(t *testing.T) {
 	testRepository.assertPathMissing(t, testRepository.worktreePath(branchName))
 }
 
+func TestRemoveMainWhenInSyncWithUpstream(t *testing.T) {
+	t.Parallel()
+
+	testRepository := newTestRepository(t)
+	require.NoError(t, testRepository.runTimber(t, "create", at(testRepoName, "main")).err)
+
+	result := testRepository.runTimber(t, "remove", at(testRepoName, "main"))
+	require.NoError(t, result.err, result.stderr)
+	testRepository.assertPathMissing(t, testRepository.worktreePath("main"))
+}
+
 func TestRemoveFailsWhenUnmergedWithoutForce(t *testing.T) {
 	t.Parallel()
 	const branchName = "feature/unmerged"

internal/timber/repository.go

@@ -62,8 +62,11 @@ func (x *Repository) branchExists(branchName string) (bool, error) {
 func (x *Repository) branchMergedToUpstream(branchName string, branchRef referenceName, upstreamRef referenceName) (bool, error) {
 	// A self-named upstream (foo tracking origin/foo) is trivially
 	// contained after a push; it says nothing about landing on the
-	// upstream branch, so never treat it as merged.
-	if isSelfNamedUpstream(branchName, upstreamRef) {
+	// upstream branch, so never treat it as merged. The default branch
+	// tracking itself (main tracking origin/main) is the exception: its
+	// upstream is the landing branch, so containment means everything
+	// local is pushed and safe to remove.
+	if isSelfNamedUpstream(branchName, upstreamRef) && !x.isDefaultUpstream(upstreamRef) {
 		return false, nil
 	}
 
@@ -89,6 +92,16 @@ func (x *Repository) branchMergedToUpstream(branchName string, branchRef referen
 	return false, err
 }
 
+// isDefaultUpstream reports whether ref is the remote-tracking ref of the
+// repository's default branch (for example refs/remotes/origin/main).
+func (x *Repository) isDefaultUpstream(ref referenceName) bool {
+	defaultBranch, err := x.remoteHeadBranch()
+	if err != nil {
+		return false
+	}
+	return string(ref) == remoteRefPrefix+defaultBranch
+}
+
 func (x *Repository) branchStillExists(branchRef referenceName) (bool, error) {
 	_, err := x.git("show-ref", "--verify", "--quiet", string(branchRef))
 	if err == nil {