scmutil: accept multiple predecessors in 'replacements' (API)...
scmutil: accept multiple predecessors in 'replacements' (API)
This changeset makes 'cleanupnodes' accepts multiple predecessors as
`replacements` keys. The same as it accepts multiple successors as
`replacements` values. To avoid breaking all callers, the old and new ways are
currently valid at the same time. We'll deprecate and drop the old way later.
This change is the first step toward a better tracking of "fold" event in the
evolution history. While working on the "rewind" command (in the evolve
extension), we realized that first class tracking of folds are necessary.
We already have good tracking of splits. When walking the evolution history
from predecessors to successors, that makes for a clear distinction between
having multiple successors because of the actual splitting of a changeset or
content-divergences.
The "rewind" command allows restoring older evolution of a stack of
changesets. One of its mode walks the evolution history to automatically find
appropriate predecessors. This means walking from successors to predecessors.
In this case, we need to be able to make the same distinction between an
actual fold and other cases. So we will have to track folds explicitly.
This changesets only focus on making it possible to express fold at the
`cleanupnodes` API level. The actual tracking will be implemented later.
