sidedata-exchange: rewrite sidedata on-the-fly whenever possible When a A exchanges with B, the difference of their supported sidedata categories is made, and the responsibility is always with the client to generated it: - If A pushes to B and B requires category `foo` that A does not have, A will need to generate it when sending it to B. - If A pulls from B and A needs category `foo`, it will generate `foo` before the end of the transaction. - Any category that is not required is removed. If peers are not compatible, abort. It is forbidden to rewrite sidedata for a rev that already has sidedata, since that would introduce unreachable (garbage) data in the data file, something we're not prepared for yet. Differential Revision: https://phab.mercurial-scm.org/D10032

revlog-index: add `replace_sidedata_info` method During a `pull` operation where the server does not provide sidedata, the client that requires it should generate them on-the-fly. In the generic case, we need to wait for the changelog + manifests + filelogs to be added, since we don't know what the sidedata computers might need: this means rewriting the sidedata of index entries from within the pull transaction (and no further back) right after we've added them. Both Python and C implementations only allow for rewriting the sidedata offset and length for revs within the transaction where they were created. Differential Revision: https://phab.mercurial-scm.org/D10031

revlogv2: temporarily forbid inline revlogs See inline comments. I plan to fix the underlying issue before revlogv2 is stabilized. Differential Revision: https://phab.mercurial-scm.org/D10030