tests/test-revset-dirstate-parents.t

fsmonitor: add new watchman notifications to fsmonitor extension

The fsmonitor extension currently sends state-enter and state-leave
notifications to watchman on the update operation. This commit creates
additional notifications for the following events :

- transaction creation and commit/abort. A state-enter notification will be
  sent when a transaction is created.  It will provide the working copy
  parent's hash. A state-leave notification will be sent when the
  transaction is committed or aborted. It will provide the working copy
  parent's hash.
- calls to set-parent will cause state-enter and state-leave notifications
  to be sent. The state-enter notification will be sent prior to the
  set-parent operation and the working copy parent's hash will be provided at
  this time. The state-leave notification will be sent after the set-parent
  operation completes providing the working copy parents hash.

Test Plan:
tested on dev server to check that necessary notifications were sent/received

Differential Revision: https://phab.mercurial-scm.org/D989

  $ HGENCODING=utf-8
  $ export HGENCODING

  $ try() {
  >   hg debugrevspec --debug $@
  > }

  $ log() {
  >   hg log --template '{rev}\n' -r "$1"
  > }

  $ hg init repo
  $ cd repo

  $ try 'p1()'
  (func
    (symbol 'p1')
    None)
  * set:
  <baseset []>
  $ try 'p2()'
  (func
    (symbol 'p2')
    None)
  * set:
  <baseset []>
  $ try 'parents()'
  (func
    (symbol 'parents')
    None)
  * set:
  <baseset+ []>

null revision
  $ log 'p1()'
  $ log 'p2()'
  $ log 'parents()'

working dir with a single parent
  $ echo a > a
  $ hg ci -Aqm0
  $ log 'p1()'
  0
  $ log 'tag() and p1()'
  $ log 'p2()'
  $ log 'parents()'
  0
  $ log 'tag() and parents()'

merge in progress
  $ echo b > b
  $ hg ci -Aqm1
  $ hg up -q 0
  $ echo c > c
  $ hg ci -Aqm2
  $ hg merge -q
  $ log 'p1()'
  2
  $ log 'p2()'
  1
  $ log 'tag() and p2()'
  $ log 'parents()'
  1
  2

  $ cd ..