Previously, ltree_prefix_eq_ci() used lowercasing with the default collation; while ltree_crc32_sz() used tolower() directly. These were equivalent only if the default collation provider was libc and the encoding was single-byte. Change both to use casefolding with the default collation. Backpatch through 18, where the casefolding APIs were introduced. The bug exists in earlier versions, but would require some adaptation. A REINDEX is required for ltree indexes where the database default collation is not libc. Reviewed-by: Chao Li <li.evan.chao@gmail.com> Reviewed-by: Peter Eisentraut <peter@eisentraut.org> Backpatch-through: 18 Discussion: https://postgr.es/m/450ceb6260cad30d7afdf155d991a9caafee7c0d.camel@j-davis.com Discussion: https://postgr.es/m/01fc00fd66f641b9693d4f9f1af0ccf44cbdfbdf.camel@j-davis.com