tests/test-missing-capability.t

rust-nodemap: accounting for dead blocks

By the very append-only nature of the `NodeTree`, inserting
new blocks has the effect of making some of the older ones
useless as they become unreachable.

Therefore some automatic housekeeping will need to be provided.
This is standard procedure in the word of databases, under names
such as "repack" or "vacuum".

The new `masked_readonly_blocks()` will provide callers with
useful information to decide if the nodetree is ripe for
repacking, but all the `NodeTree` can provide is how many
blocks have been masked in the currently mutable part. Analysing
the readonly part would be way too long to do it for each
transaction and defeat the whole purpose of nodemap persistence.
Serializing callers (from the Python layer) will get this figure
before each extraction and maintain an aggregate counter of
unreachable blocks separately.

Note: at this point, the most efficient repacking is just to restart
afresh with a full rescan.

Differential Revision: https://phab.mercurial-scm.org/D8097

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!
  [255]