tests/test-dirstate-backup.t

templater: define interface for objects requiring unwraphybrid()

Prepares for introducing another hybrid-like data type. show() takes context
as an argument so a wrapper class may render its items by pre-configured
template:

  def show(self, context, mapping):
      return (context.expand(self._tmpl, mapping + lm) for lm in self._mappings)

Set up

  $ hg init repo
  $ cd repo

Try to import an empty patch

  $ hg import --no-commit - <<EOF
  > EOF
  applying patch from stdin
  abort: stdin: no diffs found
  [255]

No dirstate backups are left behind

  $ ls .hg/dirstate* | sort
  .hg/dirstate