tests/test-merge8.t

changegroup: use a copy of hookargs when invoking the changegroup hook

addchangegroup creates a runhook function that is used to invoke the
changegroup and incoming hooks, but at the time the function is called,
the contents of hookargs associated with the transaction may have been
modified externally. For instance, bundle2 code affects it with
obsolescence markers and bookmarks info.

It also creates problems when a single transaction is used with multiple
changegroups added (as per an upcoming change), whereby the contents
of hookargs are that of after adding a latter changegroup when invoking
the hook for the first changegroup.

Test for changeset ba7c74081861
(update dirstate correctly for non-branchmerge updates)
  $ hg init a
  $ cd a
  $ echo a > a
  $ hg add a
  $ hg commit -m a
  $ cd ..
  $ hg clone a b
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd a
  $ hg mv a b
  $ hg commit -m move
  $ echo b >> b
  $ hg commit -m b
  $ cd ../b
  $ hg pull ../a
  pulling from ../a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 1 files
  (run 'hg update' to get a working copy)
  $ hg update
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ cd ..