view mercurial/utils/__init__.py @ 40000:0b24fcd88066

dagop: extract descendants() from revlog module

This method needs to be implemented in other storage backends and is
generic if we parameterize the functions for retrieving revision
numbers and parent revision numbers.

Let's extract it to dagop so backends don't need to reinvent the
wheel.

I'm not too worried about performance overhead of the extra function
call because I don't expect anyone to be calling descendants() in a
tight loop.

Differential Revision: https://phab.mercurial-scm.org/D4794