def checksubstate(repo, baserev=None):
    """return list of subrepos at a different revision than substate.
    Abort if any subrepos have uncommitted changes."""
    inclsubs = []
    wctx = repo[None]
    if baserev:
        bctx = repo[baserev]
    else:
        bctx = wctx.p1()
    for s in sorted(wctx.substate):
        wctx.sub(s).bailifchanged(True)
        if s not in bctx.substate or bctx.sub(s).dirty():
            inclsubs.append(s)
    return inclsubs
