sidedata-exchange: add `wanted_sidedata` and `sidedata_computers` to repos...
sidedata-exchange: add `wanted_sidedata` and `sidedata_computers` to repos
Each repo will advertise the sidedata categories it requires (categories being
unique and canonical), and have a set of "computers", functions to generate
sidedata from `(repo, revlog, rev, previous_sidedata)`, for a given category.
The set of computers can be a superset of the set of the wanted categories, but
not smaller: repos are expected to be coherent in their handling of sidedata.
Differential Revision:
https://phab.mercurial-scm.org/D10028
