dirstate-tree: Keep a counter of descendant nodes that have an entry...
dirstate-tree: Keep a counter of descendant nodes that have an entry
… and change the `DirstateMap::has_dir` method to be based on this counter
being non-zero instead of the mere presence of a node.
A node with zero descendent with an entry currently should be removed from
the tree, but soon we’ll make the dirstate track additional nodes.
(Specifically, for non-ignored directories in order to keep track of their
mtime and optimize status by doing fewer `read_dir` calls.)
Differential Revision:
https://phab.mercurial-scm.org/D10922
