This time, they are distinct implementations because the problem they are solving is inherently different.
For listing children of a given name, we *have* to walk the entire library (since we only have tag -> FROM mappings, not the reverse, which is fundamentally the question that "children" answers).
On the flip side, listing the parents of a given name is as straightforward as looking up the FROM values and walking until we can't anymore.
In my own testing, these new implementations are significantly more correct, and handle more edge cases (including things we couldn't support before like `bashbrew children --depth=1 scratch`, `bashbrew children mcr.microsoft.com/windows/servercore`, etc).
They also more correctly handle edge cases like tags that are `FROM` a "`SharedTag`" such that they don't walk up/down both sides of the tree (for example, `orientdb:3.2` -> `FROM eclipse-temurin:8-jdk`, which is both Windows *and* Linux, even though `orientdb:3.2` is Linux-only).
Tianon Gravi