tests/test-issue1993.t

copies: fix crash on in changeset-centric tracing from commit to itself

When we trace copies from a changeset to itself, the "work" queue ends
up empty and we hit the "assert False" after it.

It was only the last of the three added tests that failed before this
patch. That is because the other two cases have fast paths, so
_committedforwardcopies() is never reached.

Differential Revision: https://phab.mercurial-scm.org/D6675

  $ hg init a
  $ cd a
  $ echo a > a
  $ hg ci -Am0
  adding a
  $ echo b > b
  $ hg ci -Am1
  adding b
  $ hg tag -r0 default
  warning: tag default conflicts with existing branch name
  $ hg log
  changeset:   2:30a83d1e4a1e
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added tag default for changeset f7b1eb17ad24
  
  changeset:   1:925d80f479bb
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     1
  
  changeset:   0:f7b1eb17ad24
  tag:         default
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     0
  
  $ hg update 'tag(default)'
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ hg parents
  changeset:   0:f7b1eb17ad24
  tag:         default
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     0
  
  $ hg update 'branch(default)'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg parents
  changeset:   2:30a83d1e4a1e
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added tag default for changeset f7b1eb17ad24
  

  $ cd ..