revset-benchmark: use a generic revset to test `heads(commonancestors())` This allow to benchmark revset performance in other repositories than just the mercurial one.

revlog: reintroduce `revlog.descendant` as deprecated Reintroduce `revlog.descendant` to help extensions authors update their extensions in order to use the new API.

context: reintroduce `ctx.descendant` as deprecated Reintroduce `ctx.descendant` to help extensions authors update their extensions in order to use the new API.

obsolete: explode if metadata contains invalid UTF-8 sequence (API) The current metadata API can be a source of bugs since it forces callers to process encoding conversion by themselves. So let's make it reject bad data as a last ditch. I assume there's no metadata field which is supposed to store arbitrary BLOB like transplant_source.

obsolete: store user name and note in UTF-8 (issue5754) (BC) Before, user names were stored in local encoding and transferred across repositories, which made it impossible to restore non-ASCII user names on different platforms. This patch fixes new markers to be encoded in UTF-8 and decoded back to local encoding when displaying. Existing markers are unfixable so they may result in mojibake. I don't like the API that requires metadata dict to be UTF-8 encoded, which is a source of bugs, but there's no abstraction layer to process the encoding thingy efficiently. So we apply the same rule as extras dict to obsstore metadata.

obsolete: clarify users in markerusers() never contain None

revset: special case commonancestors(none()) to be empty set This matches the behavior of ancestor(none()). From an implementation perspective, ancestor() and commonancestors() are intersection, and ancestors() is union, so it would make some sense that commonancestors(none()) returned all revisions. However, ancestor(none()) isn't implemented as such, which breaks ancestor(x) == max(commonancestors(x)). From a user perspective, ancestors of nothing is nothing whichever type of operation the ancestor predicate does.

revset: clarify heads() order doesn't matter while computing common ancestors Follows up 5460926352ee and 52f19a840543.

hghave: require clang-format >= 6 due to output change

cext: reformat with clang-format 6.0 It appears some changes in clang-format affect our code. I didn't dig into that deeper since the new output looks better.