tests/test-phabricator.t

cext-revlog: fixed  __delitem__ for uninitialized nodetree

This is a bug in a code path that's seldom used, because in practice
(at least in the whole test suite), calls to `del index[i:j]` currently
just don't happen before the nodetree has been initialized.
However, in our current work to replace the nodetree by a Rust implementation,
this is of course systematic.

In `index_slice_del()`, if the slice start is smaller than `self->length`,
the whole of `self->added` has to be cleared.

Before this change, the clearing was done only by the call to
`index_invalidate_added(self, 0)`, that happens only for initialized
nodetrees. Hence the removal was effective only from `start` to `self->length`.

The consequence is index corruption, with bogus results in subsequent calls,
and in particular errors such as `ValueError("parent out of range")`, due to
the fact that parents of entries in `self->added` are now just invalid.

This is detected by the rebase tests, under conditions that the nodetree
of revlog.c is never initialized. The provided specific test is more direct.

Differential Revision: https://phab.mercurial-scm.org/D7603

#require vcr
  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > phabricator = 
  > EOF
  $ hg init repo
  $ cd repo
  $ cat >> .hg/hgrc <<EOF
  > [phabricator]
  > url = https://phab.mercurial-scm.org/
  > callsign = HG
  > 
  > [auth]
  > hgphab.schemes = https
  > hgphab.prefix = phab.mercurial-scm.org
  > # When working on the extension and making phabricator interaction
  > # changes, edit this to be a real phabricator token. When done, edit
  > # it back. The VCR transcripts will be auto-sanitised to replace your real
  > # token with this value.
  > hgphab.phabtoken = cli-hahayouwish
  > EOF
  $ VCR="$TESTDIR/phabricator"