tests/test-debugindexdot.t

context: make repo[<filtered binary nodeid>] match node

If you pass in a binary nodeid of a filtered node to repo.__getitem__,
it would run through this code:

    try:
        self._node = changeid
	self._rev = repo.changelog.rev(changeid)
	return
    except error.FilteredLookupError:
        raise
    except LookupError:
         pass

However, repo.changelog.rev() would raise a FilteredLookupError, not
FilteredRepoLookupError. Instead, we would hit the "except
LookupError" and continue, trying to interpret the nodeid as a
bookmark etc. The end result would be an error like this:

  abort: unknown revision 'ddadbd7c40ef8b8ad6d0d01a7a842092fc431798'!

After this patch, it would instead be:

  abort: 00changelog.i@ddadbd7c40ef8b8ad6d0d01a7a842092fc431798: filtered node!

This only happens when we get a binary nodeid, which means it's not
string directly from the user, so it would be a programming error if
it happened. It's therefore a little hard to test (I checked
test-context.py, but it doesn't use obsmarkers).

It looks like this has been wrong ever since dc25ed84bee8 (changectx:
issue a FilteredRepoLookupError when applicable, 2014-10-15).

Differential Revision: https://phab.mercurial-scm.org/D3144

Just exercise debugindexdot
Create a short file history including a merge.
  $ hg init t
  $ cd t
  $ echo a > a
  $ hg ci -qAm t1 -d '0 0'
  $ echo a >> a
  $ hg ci -m t2 -d '1 0'
  $ hg up -qC 0
  $ echo b >> a
  $ hg ci -m t3 -d '2 0'
  created new head
  $ HGMERGE=true hg merge -q
  $ hg ci -m merge -d '3 0'

  $ hg debugindexdot a
  digraph G {
  	-1 -> 0
  	0 -> 1
  	0 -> 2
  	2 -> 3
  	1 -> 3
  }

  $ cd ..