In pre-monorepo times the svn staging directory was .git/svn. The below error message wasn't mentioning the new name yet.
Can't push git rev 104cfa289d9 because svn status is not empty: ! llvm/trunk/include/llvm
Can't push git rev 104cfa289d9 because status in svn staging dir (.git/llvm-upstream-svn) is not empty: ! llvm/trunk/include/llvm