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

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"""utilities to assist in working with pygit2"""

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from __future__ import absolute_import

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from mercurial.node import bin, hex, nullid

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from mercurial import pycompat

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def togitnode(n):

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    """Wrapper to convert a Mercurial binary node to a unicode hexlified node.

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    pygit2 and sqlite both need nodes as strings, not bytes.

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    """

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    assert len(n) == 20

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    return pycompat.sysstr(hex(n))

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def fromgitnode(n):

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    """Opposite of togitnode."""

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    assert len(n) == 40

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    if pycompat.ispy3:

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        return bin(n.encode('ascii'))

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    return bin(n)

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nullgit = togitnode(nullid)