tests/test-missing-capability.t

sharesafe: add functionality to automatically downgrade shares

Reasoning is same as previous patch which adds automatic upgrade support.

Downgrade is required as if automatic upgrade is enabled, all shares upgrade and
then source repository downgrades, shares won't work. We need to downgrade them.

Differential Revision: https://phab.mercurial-scm.org/D9680

Checking how hg behaves when one side of a pull/push doesn't support
some capability (because it's running an older hg version, usually).

  $ hg init repo1
  $ cd repo1
  $ echo a > a; hg add -q a; hg commit -q -m a
  $ hg bookmark a
  $ hg clone -q . ../repo2
  $ cd ../repo2

  $ touch $TESTTMP/disable-lookup.py
  $ disable_cap() {
  >   rm -f $TESTTMP/disable-lookup.pyc # pyc caching is buggy
  >   cat <<EOF > $TESTTMP/disable-lookup.py
  > from mercurial import extensions, wireprotov1server
  > def wcapabilities(orig, *args, **kwargs):
  >   cap = orig(*args, **kwargs)
  >   cap.remove(b'$1')
  >   return cap
  > extensions.wrapfunction(wireprotov1server, '_capabilities', wcapabilities)
  > EOF
  > }
  $ cat >> ../repo1/.hg/hgrc <<EOF
  > [extensions]
  > disable-lookup = $TESTTMP/disable-lookup.py
  > EOF
  $ cat >> .hg/hgrc <<EOF
  > [ui]
  > ssh = "$PYTHON" "$TESTDIR/dummyssh"
  > EOF

  $ hg pull ssh://user@dummy/repo1 -r tip -B a
  pulling from ssh://user@dummy/repo1
  no changes found

  $ disable_cap lookup
  $ hg pull ssh://user@dummy/repo1 -r tip -B a
  pulling from ssh://user@dummy/repo1
  abort: other repository doesn't support revision lookup, so a rev cannot be specified.
  [255]

  $ disable_cap pushkey
  $ hg pull ssh://user@dummy/repo1 -r tip -B a
  pulling from ssh://user@dummy/repo1
  abort: remote bookmark a not found!
  [10]