Properly handle transplant_source in changeset extra fields
Mercurial changeset can contain extra data in it, notably a transplant_source
field
referencing another changeset id. In contrary to other extra fields, this one stores
the changeset reference in binary instead of using the hexadecimal representation.
So to ease original changeset extra data exploitation and avoid decoding errors, prefer to store the hexadecimal representation of the changeset id in the swh revision metadata.
Related #1729 (closed)
Test Plan
A new test case has been added.
Migrated from D1507 (view on Phabricator)