tests/test-revisions.t

wireprotov2: allow multiple fields to follow revision maps

The *data wire protocol commands emit a series of CBOR values.
Because revision/delta data may be large, their data is emitted
outside the map as a top-level bytestring value.

Before this commit, we'd emit a single optional bytestring
value after the revision descriptor map. This got the job done.
But it was limiting in that we could only send a single field.
And, it required the consumer to know that the presence of a
key in the map implied the existence of a following bytestring
value.

This commit changes the encoding strategy so top-level bytestring
values in the stream are explicitly denoted in a "fieldsfollowing"
key. This key contains an array defining what fields that follow
and the expected size of each field.

By defining things this way, we can easily send N bytestring
values without any ambiguity about their order. In addition,
clients only need to know how to parse ``fieldsfollowing`` to
know if extra values are present.

Because this breaks backwards compatibility, we've bumped the version
number of the wire protocol version 2 API endpoint.

Differential Revision: https://phab.mercurial-scm.org/D4620

  $ hg init repo
  $ cd repo

  $ echo 0 > a
  $ hg ci -qAm 0
  $ for i in 5 8 14 43 167; do
  >   hg up -q 0
  >   echo $i > a
  >   hg ci -qm $i
  > done
  $ cat <<EOF >> .hg/hgrc
  > [alias]
  > l = log -T '{rev}:{shortest(node,1)}\n'
  > EOF

  $ hg l
  5:00f
  4:7ba5d
  3:7ba57
  2:72
  1:9
  0:b
  $ cat <<EOF >> .hg/hgrc
  > [experimental]
  > revisions.disambiguatewithin=not 4
  > EOF
  $ hg l
  5:0
  4:7ba5d
  3:7b
  2:72
  1:9
  0:b
9 was unambiguous and still is
  $ hg l -r 9
  1:9
7 was ambiguous and still is
  $ hg l -r 7
  abort: 00changelog.i@7: ambiguous identifier!
  [255]
7b is no longer ambiguous
  $ hg l -r 7b
  3:7b

  $ cd ..