annotate hgext/git/index.py @ 44477:ad718271a9eb

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

from __future__ import absolute_import

import collections
import os
import sqlite3

import pygit2

from mercurial.i18n import _

from mercurial import (
    encoding,
    error,
    node as nodemod,
    pycompat,
)

from . import gitutil


_CURRENT_SCHEMA_VERSION = 1
_SCHEMA = (
    """
CREATE TABLE refs (
  -- node and name are unique together. There may be more than one name for
  -- a given node, and there may be no name at all for a given node (in the
  -- case of an anonymous hg head).
  node TEXT NOT NULL,
  name TEXT
);

-- The "possible heads" of the repository, which we use to figure out
-- if we need to re-walk the changelog.
CREATE TABLE possible_heads (
  node TEXT NOT NULL
);

-- The topological heads of the changelog, which hg depends on.
CREATE TABLE heads (
  node TEXT NOT NULL
);

-- A total ordering of the changelog
CREATE TABLE changelog (
  rev INTEGER NOT NULL PRIMARY KEY,
  node TEXT NOT NULL,
  p1 TEXT,
  p2 TEXT
);

CREATE UNIQUE INDEX changelog_node_idx ON changelog(node);
CREATE UNIQUE INDEX changelog_node_rev_idx ON changelog(rev, node);

-- Changed files for each commit, which lets us dynamically build
-- filelogs.
CREATE TABLE changedfiles (
  node TEXT NOT NULL,
  filename TEXT NOT NULL,
  -- 40 zeroes for deletions
  filenode TEXT NOT NULL,
-- to handle filelog parentage:
  p1node TEXT,
  p1filenode TEXT,
  p2node TEXT,
  p2filenode TEXT
);

CREATE INDEX changedfiles_nodes_idx
  ON changedfiles(node);

PRAGMA user_version=%d
"""
    % _CURRENT_SCHEMA_VERSION
)


def _createdb(path):
    # print('open db', path)
    # import traceback
    # traceback.print_stack()
    db = sqlite3.connect(encoding.strfromlocal(path))
    db.text_factory = bytes

    res = db.execute('PRAGMA user_version').fetchone()[0]

    # New database.
    if res == 0:
        for statement in _SCHEMA.split(';'):
            db.execute(statement.strip())

        db.commit()

    elif res == _CURRENT_SCHEMA_VERSION:
        pass

    else:
        raise error.Abort(_(b'sqlite database has unrecognized version'))

    db.execute('PRAGMA journal_mode=WAL')

    return db


_OUR_ORDER = (
    pygit2.GIT_SORT_TOPOLOGICAL | pygit2.GIT_SORT_TIME | pygit2.GIT_SORT_REVERSE
)

_DIFF_FLAGS = 1 << 21  # GIT_DIFF_FORCE_BINARY, which isn't exposed by pygit2


def _find_nearest_ancestor_introducing_node(
    db, gitrepo, file_path, walk_start, filenode
):
    """Find the nearest ancestor that introduces a file node.

    Args:
      db: a handle to our sqlite database.
      gitrepo: A pygit2.Repository instance.
      file_path: the path of a file in the repo
      walk_start: a pygit2.Oid that is a commit where we should start walking
                  for our nearest ancestor.

    Returns:
      A hexlified SHA that is the commit ID of the next-nearest parent.
    """
    assert isinstance(file_path, str), 'file_path must be str, got %r' % type(
        file_path
    )
    assert isinstance(filenode, str), 'filenode must be str, got %r' % type(
        filenode
    )
    parent_options = {
        row[0].decode('ascii')
        for row in db.execute(
            'SELECT node FROM changedfiles '
            'WHERE filename = ? AND filenode = ?',
            (file_path, filenode),
        )
    }
    inner_walker = gitrepo.walk(walk_start, _OUR_ORDER)
    for w in inner_walker:
        if w.id.hex in parent_options:
            return w.id.hex
    raise error.ProgrammingError(
        'Unable to find introducing commit for %s node %s from %s',
        (file_path, filenode, walk_start),
    )


def fill_in_filelog(gitrepo, db, startcommit, path, startfilenode):
    """Given a starting commit and path, fill in a filelog's parent pointers.

    Args:
      gitrepo: a pygit2.Repository
      db: a handle to our sqlite database
      startcommit: a hexlified node id for the commit to start at
      path: the path of the file whose parent pointers we should fill in.
      filenode: the hexlified node id of the file at startcommit

    TODO: make filenode optional
    """
    assert isinstance(
        startcommit, str
    ), 'startcommit must be str, got %r' % type(startcommit)
    assert isinstance(
        startfilenode, str
    ), 'startfilenode must be str, got %r' % type(startfilenode)
    visit = collections.deque([(startcommit, startfilenode)])
    while visit:
        cnode, filenode = visit.popleft()
        commit = gitrepo[cnode]
        parents = []
        for parent in commit.parents:
            t = parent.tree
            for comp in path.split('/'):
                try:
                    t = gitrepo[t[comp].id]
                except KeyError:
                    break
            else:
                introducer = _find_nearest_ancestor_introducing_node(
                    db, gitrepo, path, parent.id, t.id.hex
                )
                parents.append((introducer, t.id.hex))
        p1node = p1fnode = p2node = p2fnode = gitutil.nullgit
        for par, parfnode in parents:
            found = int(
                db.execute(
                    'SELECT COUNT(*) FROM changedfiles WHERE '
                    'node = ? AND filename = ? AND filenode = ? AND '
                    'p1node NOT NULL',
                    (par, path, parfnode),
                ).fetchone()[0]
            )
            if found == 0:
                assert par is not None
                visit.append((par, parfnode))
        if parents:
            p1node, p1fnode = parents[0]
        if len(parents) == 2:
            p2node, p2fnode = parents[1]
        if len(parents) > 2:
            raise error.ProgrammingError(
                b"git support can't handle octopus merges"
            )
        db.execute(
            'UPDATE changedfiles SET '
            'p1node = ?, p1filenode = ?, p2node = ?, p2filenode = ? '
            'WHERE node = ? AND filename = ? AND filenode = ?',
            (p1node, p1fnode, p2node, p2fnode, commit.id.hex, path, filenode),
        )
    db.commit()


def _index_repo(gitrepo, db, progress_factory=lambda *args, **kwargs: None):
    # Identify all references so we can tell the walker to visit all of them.
    all_refs = gitrepo.listall_references()
    possible_heads = set()
    prog = progress_factory(b'refs')
    for pos, ref in enumerate(all_refs):
        if prog is not None:
            prog.update(pos)
        if not (
            ref.startswith('refs/heads/')  # local branch
            or ref.startswith('refs/tags/')  # tag
            or ref.startswith('refs/remotes/')  # remote branch
            or ref.startswith('refs/hg/')  # from this extension
        ):
            continue
        try:
            start = gitrepo.lookup_reference(ref).peel(pygit2.GIT_OBJ_COMMIT)
        except ValueError:
            # No commit to be found, so we don't care for hg's purposes.
            continue
        possible_heads.add(start.id)
    # Optimization: if the list of heads hasn't changed, don't
    # reindex, the changelog. This doesn't matter on small
    # repositories, but on even moderately deep histories (eg cpython)
    # this is a very important performance win.
    #
    # TODO: we should figure out how to incrementally index history
    # (preferably by detecting rewinds!) so that we don't have to do a
    # full changelog walk every time a new commit is created.
    cache_heads = {x[0] for x in db.execute('SELECT node FROM possible_heads')}
    walker = None
    cur_cache_heads = {h.hex for h in possible_heads}
    if cur_cache_heads == cache_heads:
        return
    for start in possible_heads:
        if walker is None:
            walker = gitrepo.walk(start, _OUR_ORDER)
        else:
            walker.push(start)

    # Empty out the existing changelog. Even for large-ish histories
    # we can do the top-level "walk all the commits" dance very
    # quickly as long as we don't need to figure out the changed files
    # list.
    db.execute('DELETE FROM changelog')
    if prog is not None:
        prog.complete()
    prog = progress_factory(b'commits')
    # This walker is sure to visit all the revisions in history, but
    # only once.
    for pos, commit in enumerate(walker):
        if prog is not None:
            prog.update(pos)
        p1 = p2 = nodemod.nullhex
        if len(commit.parents) > 2:
            raise error.ProgrammingError(
                (
                    b"git support can't handle octopus merges, "
                    b"found a commit with %d parents :("
                )
                % len(commit.parents)
            )
        if commit.parents:
            p1 = commit.parents[0].id.hex
        if len(commit.parents) == 2:
            p2 = commit.parents[1].id.hex
        db.execute(
            'INSERT INTO changelog (rev, node, p1, p2) VALUES(?, ?, ?, ?)',
            (pos, commit.id.hex, p1, p2),
        )

        num_changedfiles = db.execute(
            "SELECT COUNT(*) from changedfiles WHERE node = ?",
            (commit.id.hex,),
        ).fetchone()[0]
        if not num_changedfiles:
            files = {}
            # I *think* we only need to check p1 for changed files
            # (and therefore linkrevs), because any node that would
            # actually have this commit as a linkrev would be
            # completely new in this rev.
            p1 = commit.parents[0].id.hex if commit.parents else None
            if p1 is not None:
                patchgen = gitrepo.diff(p1, commit.id.hex, flags=_DIFF_FLAGS)
            else:
                patchgen = commit.tree.diff_to_tree(
                    swap=True, flags=_DIFF_FLAGS
                )
            new_files = (p.delta.new_file for p in patchgen)
            files = {
                nf.path: nf.id.hex
                for nf in new_files
                if nf.id.raw != nodemod.nullid
            }
            for p, n in files.items():
                # We intentionally set NULLs for any file parentage
                # information so it'll get demand-computed later. We
                # used to do it right here, and it was _very_ slow.
                db.execute(
                    'INSERT INTO changedfiles ('
                    'node, filename, filenode, p1node, p1filenode, p2node, '
                    'p2filenode) VALUES(?, ?, ?, ?, ?, ?, ?)',
                    (commit.id.hex, p, n, None, None, None, None),
                )
    db.execute('DELETE FROM heads')
    db.execute('DELETE FROM possible_heads')
    for hid in possible_heads:
        h = hid.hex
        db.execute('INSERT INTO possible_heads (node) VALUES(?)', (h,))
        haschild = db.execute(
            'SELECT COUNT(*) FROM changelog WHERE p1 = ? OR p2 = ?', (h, h)
        ).fetchone()[0]
        if not haschild:
            db.execute('INSERT INTO heads (node) VALUES(?)', (h,))

    db.commit()
    if prog is not None:
        prog.complete()


def get_index(gitrepo, progress_factory=lambda *args, **kwargs: None):
    cachepath = os.path.join(
        pycompat.fsencode(gitrepo.path), b'..', b'.hg', b'cache'
    )
    if not os.path.exists(cachepath):
        os.makedirs(cachepath)
    dbpath = os.path.join(cachepath, b'git-commits.sqlite')
    db = _createdb(dbpath)
    # TODO check against gitrepo heads before doing a full index
    # TODO thread a ui.progress call into this layer
    _index_repo(gitrepo, db, progress_factory)
    return db