rust: dagop.headrevs() Rust counterparts...
rust: dagop.headrevs() Rust counterparts
This introduces two Rust implementations for `mercurial.dagop.headrevs`.
The algorithm is identical to the Python version.
Depending on the caller, one or the other could be the most practical, or
the most performant, by minimizing the amount of memory copy and allocations.
Differential Revision:
https://phab.mercurial-scm.org/D5580
