hghave: add a check for pygit2 This will make it easy to use availability of pygit2 as in conditions such as `#if pygit2` and `(pygit2 !)`. It also makes it a little clearer why the test case skipped (when that happens). Differential Revision: https://phab.mercurial-scm.org/D8267

localrepo: add git extension to autoextensions list Differential Revision: https://phab.mercurial-scm.org/D8266

gitlog: implement __iter__ on changelog This allows `hg phase --force --draft -r .` to work, for example. Differential Revision: https://phab.mercurial-scm.org/D8264

gitlog: fix embarassing bug that prevented log from showing correct parents We had the correct parents in the database, but the changelog was always returning p1 for all parents. Oops. Differential Revision: https://phab.mercurial-scm.org/D8263

git: add readfast() method to manifest Mysteriously, on a different system a handful of things don't work without this, including log. This is especially odd to be because log works in the test. In any event, it's legal for readfast() to just return read(), so that's what we do. Differential Revision: https://phab.mercurial-scm.org/D8262

git: make {shortest()} return shortest *unique* prefix It used to return the prefix of the specified length as long as the full node was unique (i.e. always). Differential Revision: https://phab.mercurial-scm.org/D8256

git: skeleton of a new extension to _directly_ operate on git repos This is based in part of work I did years ago in hgit, but it's mostly new code since I'm using pygit2 instead of dulwich and the hg storage interfaces have improved. Some cleanup of old hgit code by Pulkit, which I greatly appreciate. test-git-interop.t does not cover a whole lot of cases, but it passes. It includes status, diff, making a new commit, and `hg annotate` working on the git repository. This is _not_ (yet) production quality code: this is an experiment. Known technical debt lurking in this implementation: * Writing bookmarks just totally ignores transactions. * The way progress is threaded down into the gitstore is awful. * Ideally we'd find a way to incrementally reindex DAGs. I'm not sure how to do that efficiently, so we might need a "known only fast-forwards" mode on the DAG indexer for use on `hg commit` and friends. * We don't even _try_ to do anything reasonable for `hg pull` or `hg push`. * Mercurial need an interface for the changelog type. Tests currently require git 2.24 as far as I'm aware: `git status` has some changed output that I didn't try and handle in a compatible way. This patch has produced some interesting cleanups, most recently on the manifest type. I expect continuing down this road will produce other meritorious cleanups throughout our code. Differential Revision: https://phab.mercurial-scm.org/D6734

hg-core: add a compilation error if trying to compile outside of Linux For now, we can only provide support for Linux in `hg-core`, so we have to be explicit about it in case anyone wonders why their Dirstate is suddenly broken, or why the crate does not compile (on Windows for example). Differential Revision: https://phab.mercurial-scm.org/D8246

gzip: use the stdlib version with python 3 (issue6284) It turned out that the stdlib gained the feature we missed in python 3.1. We can now use it directly.

gzip: indent the custom Gzip code We need a new conditional in the next changesets (Adding 3.8 support). We do the large code move beforehand for clarity.

gzip: rename the argument to `mtime` to match upstream python Python gained the feature we missed in 3.1. The argument name is `mtime`. We align our version for consistency.

heptapod-ci: run the test from outside the test directory This will help detecting case where this is broken.