rust-dirs-multiset: improve temporary error message While we wait on a future patch that could verify that the paths passed to `DirsMultiset` have been audited, we still need to handle this error. This patch makes it easier to bubble up and makes the error clearer. Also, this patch introduces the `subslice_index` function that could be useful for other - albeit niche - purposes. Differential Revision: https://phab.mercurial-scm.org/D7921

exchange: check the `ui.clonebundleprefers` form while processing (issue6257) Otherwise the clone command will emit a long stacktrace if there is no `=` character. Differential Revision: https://phab.mercurial-scm.org/D7969

copies: add a new test dedicated to testing chain of changeset with merge The copies test we currently have usually focus on simple case that do not dive too much into longer chains involving merges. This new test file focus on extensive testing of these case to validate their behavior and make sure the various copies algorithm have the same behavior. And… actually these test are currently broken for the changeset centric algorithm since 99ebde4fec99, but it went undetected because these case were not tested. Differential Revision: https://phab.mercurial-scm.org/D8078

hgext: initial version of fastexport extension Differential Revision: https://phab.mercurial-scm.org/D7733