revlog: calculate base revisions iteratively
This is in preparation for generaldelta, where the revlog entry base field is
reinterpreted as the deltaparent. For that reason we also rename the base
function to chainbase.
Without generaldelta, performance is unaffected, but generaldelta will suffer
from this in _addrevision, since delta chains will be walked repeatedly.
A cache has been added to eliminate this problem completely.
$ hg init
$ echo a > a
$ hg ci -qAm 'add a'
$ hg init subrepo
$ echo 'subrepo = http://example.net/libfoo' > .hgsub
$ hg ci -qAm 'added subrepo'
$ hg up -qC 0
$ echo ax > a
$ hg ci -m 'changed a'
created new head
$ hg up -qC 1
$ cd subrepo
$ echo b > b
$ hg add b
$ cd ..
Should fail, since there are added files to subrepo:
$ hg merge
abort: outstanding uncommitted changes in subrepository 'subrepo'
[255]