def _trimchunk(revlog, revs, startidx, endidx=None):
    """returns revs[startidx:endidx] without empty trailing revs

    Doctest Setup
    >>> revlog = _testrevlog([
    ...  5,  #0
    ...  10, #1
    ...  12, #2
    ...  12, #3 (empty)
    ...  17, #4
    ...  21, #5
    ...  21, #6 (empty)
    ... ])

    Contiguous cases:
    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 0)
    [0, 1, 2, 3, 4, 5]
    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 0, 5)
    [0, 1, 2, 3, 4]
    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 0, 4)
    [0, 1, 2]
    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 2, 4)
    [2]
    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 3)
    [3, 4, 5]
    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 3, 5)
    [3, 4]

    Discontiguous cases:
    >>> _trimchunk(revlog, [1, 3, 5, 6], 0)
    [1, 3, 5]
    >>> _trimchunk(revlog, [1, 3, 5, 6], 0, 2)
    [1]
    >>> _trimchunk(revlog, [1, 3, 5, 6], 1, 3)
    [3, 5]
    >>> _trimchunk(revlog, [1, 3, 5, 6], 1)
    [3, 5]
    """
    length = revlog.length
    if endidx is None:
        endidx = len(revs)
    if revs[endidx - 1] < len(revlog):
        while endidx > 1 and endidx > startidx and length(revs[endidx - 1]
            ) == 0:
            endidx -= 1
    return revs[startidx:endidx]
