reachableroots: if allocating a new set fails, use PyErr_NoMemory() My inspection of the implementation of PySet_New() indicates that it does *not* reliably set an exception in the cases where it returns NULL (as far as I can tell it'll never do that!), so let's set that up ourselves.

reachableroots: default to the C implementation This patch is part of a series of patches to speed up the computation of revset.reachableroots by introducing a C implementation. The main motivation is to speed up smartlog on big repositories. At the end of the series, on our big repositories the computation of reachableroots is 10-50x faster and smartlog on is 2x-5x faster. Before this patch, reachableroots was computed in pure Python by default. This patch makes the C implementation the default and provides a speedup for reachableroots.

changelog: add way to call the reachableroots C implementation This patch is part of a series of patches to speed up the computation of revset.reachableroots by introducing a C implementation. The main motivation is to speed up smartlog on big repositories. At the end of the series, on our big repositories the computation of reachableroots is 10-50x faster and smartlog on is 2x-5x faster. This patch allows us to call the new C implementation of reachableroots from python by creating an entry point in the changelog class.