contrib/undumprevlog

rust-changelog: introducing an intermediate `ChangelogEntry`

Before this change, client code needing to extract, e.g, the Node ID and the
description from a changeset had no other choice than calling both
`entry_for_rev()` and `data_for_rev()`. This duplicates some (limited) computation, and
more importantly imposes bad hygiene for client code: at some point of developement,
the client code would have to pass over both entry and data in its internal layers,
which at some point of development would raise the question whether they are consistent.

We introduce the intermediate `ChangelogEntry` from which both conversion to the generic
`RevlogEntry` and extraction of `ChangelogRevisionData` are possible.
It might grow some convenience methods in the future.

We keep the `data_for_rev()` method of `Changelog` for compatibility, pointing users at the more
powerful alternative.

#!/usr/bin/env python3
# Undump a dump from dumprevlog
# $ hg init
# $ undumprevlog < repo.dump


import sys
from mercurial.node import bin
from mercurial import (
    encoding,
    revlog,
    transaction,
    vfs as vfsmod,
)
from mercurial.utils import procutil

from mercurial.revlogutils import (
    constants as revlog_constants,
)

for fp in (sys.stdin, sys.stdout, sys.stderr):
    procutil.setbinary(fp)

opener = vfsmod.vfs(b'.', False)
tr = transaction.transaction(
    sys.stderr.write, opener, {b'store': opener}, b"undump.journal"
)
while True:
    l = sys.stdin.readline()
    if not l:
        break
    if l.startswith("file:"):
        f = encoding.strtolocal(l[6:-1])
        assert f.endswith(b'.i')
        r = revlog.revlog(
            opener,
            target=(revlog_constants.KIND_OTHER, b'undump-revlog'),
            radix=f[:-2],
        )
        procutil.stdout.write(b'%s\n' % f)
    elif l.startswith("node:"):
        n = bin(l[6:-1])
    elif l.startswith("linkrev:"):
        lr = int(l[9:-1])
    elif l.startswith("parents:"):
        p = l[9:-1].split()
        p1 = bin(p[0])
        p2 = bin(p[1])
    elif l.startswith("length:"):
        length = int(l[8:-1])
        sys.stdin.readline()  # start marker
        d = encoding.strtolocal(sys.stdin.read(length))
        sys.stdin.readline()  # end marker
        r.addrevision(d, tr, lr, p1, p2)

tr.close()