index: drop support for negative indexes into the index I want index[i] to work for any valid revnum including -1 (as it already does), and I also want len(index) to be the number of revisions in the index (not counting the null revision), so it cannot also support negative revision numbers other than -1 for nullid. I didn't bother removing support for it from revlog v0. Differential Revision: https://phab.mercurial-scm.org/D4019

index: handle index[-1] as nullid more explicitly I find it more intuitive to check if "pos == -1" than to first add the index length (which includes one extra item for the nullid) and compare that to "length - 1". However, because test-parseindex2.py compares the whole index (up to len(index)-1), we need to also preserve that other check for a little while more. I'll remove it soon. Differential Revision: https://phab.mercurial-scm.org/D4018

index: store nullrev as -1 in nodetree Nothing important, it just seems more natural to not map nullrev to INT_MAX. We just need to change the revision encoding a little to make space for the -1. Differential Revision: https://phab.mercurial-scm.org/D4005

index: create function for deleting node from nodetree A node is marked deleted by nt_insert(self, node, -1), but "-1" could mean so many things (notably nullrev), so let's hide it in a function. The function could possibly also remove nodes from the tree in the future (it currently only marks them deleted). Differential Revision: https://phab.mercurial-scm.org/D4004