tests/test-merge-subrepos.t

templatefilters: add "utf8" to get utf-8 bytes from local-encoding text

This will be applied prior to "|json" filter. This sounds like odd, but it
is necessary to handle local-encoding text as well as raw filename bytes.

Because filenames are bytes in Mercurial and Unix world, {filename|json} should
preserve the original byte sequence, which implies

  {x|json} -> '"' toutf8b(x) '"'

On the other hand, most template strings are in local encoding. Because
"|json" filter have to be byte-transparent to filenames, we need something to
annotate an input as a local string, that's what "|utf8" will do.

  {x|utf8|json} -> '"' toutf8b(fromlocal(x)) '"'

"|utf8" is an explicit call, so aborts if input bytes can't be converted to
UTF-8.

  $ hg init

  $ echo a > a
  $ hg ci -qAm 'add a'

  $ hg init subrepo
  $ echo 'subrepo = http://example.net/libfoo' > .hgsub
  $ hg ci -qAm 'added subrepo'

  $ hg up -qC 0
  $ echo ax > a
  $ hg ci -m 'changed a'
  created new head

  $ hg up -qC 1
  $ cd subrepo
  $ echo b > b
  $ hg add b
  $ cd ..

Should fail, since there are added files to subrepo:

  $ hg merge
  abort: uncommitted changes in subrepository 'subrepo'
  [255]