git log :/a --
'
+test_expect_success '"git log :/detached -- " should find a commit only in HEAD' '
+ test_when_finished "git checkout master" &&
+ git checkout --detach &&
+ # Must manually call `test_tick` instead of using `test_commit`,
+ # because the latter additionally creates a tag, which would make
+ # the commit reachable not only via HEAD.
+ test_tick &&
+ git commit --allow-empty -m detached &&
+ test_tick &&
+ git commit --allow-empty -m something-else &&
+ git log :/detached --
+'
+
+test_expect_success '"git log :/detached -- " should not find an orphaned commit' '
+ test_must_fail git log :/detached --
+'
+
+test_expect_success '"git log :/detached -- " should find HEAD only of own worktree' '
+ git worktree add other-tree HEAD &&
+ git -C other-tree checkout --detach &&
+ test_tick &&
+ git -C other-tree commit --allow-empty -m other-detached &&
+ git -C other-tree log :/other-detached -- &&
+ test_must_fail git log :/other-detached --
+'
+
test_expect_success '"git log -- :/a" should not be ambiguous' '
git log -- :/a
'