exchange: add fast path for subrepo check on push...
exchange: add fast path for subrepo check on push
Try to check if .hgsub and .hgsubstate exist at all before looking
for them in every changeset to be pushed. The latter can be quite
expensive for large repositories and the existance check is almost free.
Differential Revision:
https://phab.mercurial-scm.org/D11956