bokeh layout with different size elements does not pack tightly

[johnzzzzzzz]

I am trying to make a layout with 4 skinny elements tightly packed on one row followed by 1 long element in the next row.

The row of small elements packed nicely to the left before the bokeh layout refactor #3450
Now the elements are aligned in columns, with the column width equal to the max width of the elements in that column.
Is there a trick to Layout rows with multiple objects on one row that are tightly packed and a single object on the next row? Not like this

Also when using sizing_mode='fixed', I get the error:
WARNING:bokeh.core.validation.check:W-1005 (FIXED_SIZING_MODE): 'fixed' sizing mode requires width and height to be set: Column(id='1009', ...)

I am using holoviews version '1.12.5' and bokeh version '1.2.0' from a fresh install of anaconda python 2.7 as of Aug 15, 2019

import holoviews as hv
hv.extension('bokeh')
def block(height=100, width=100, color='yellow'):
    # Create a dvi of a fixed size and a colored block inside
    template = '<svg>  <rect x="0" y="0" width="{width}" height="{height}", fill="{color}"/>{color}</svg>'
    rect = template.format(**locals())
    return hv.Div(rect).opts(height=height, width=width)

layout = (
    block(width=100, height=100, color='red') + 
    block(width=100, height=100, color='blue') + 
    block(width=100, height=100, color='green') + 
    block(width=100, height=100, color='yellow') + 
    block(width=400, height=100, color='gray') 
    # block(width=10,  height=10,  color='purple') +
    # block(width=10,  height=10,  color='orange') +
    # block(width=10,  height=10,  color='brown')
).cols(4)

sizing_modes = [ None, "fixed", "stretch_width", "stretch_height", "stretch_both",
                "scale_width", "scale_height", "scale_both"]
exp = dict()
for sizing in sizing_modes:
    exp[sizing] = layout.opts(sizing_mode = sizing,
                                height=200,
                                width=400,
                                title=str(sizing),
                                clone=True)
exp['fixed']

[philippjfr]

This is not in scope for HoloViews Layout. We are planning on adding more complex layouts but if you need this now I'd recommend using Panel Rows and Columns. The generalization of layouts is covered by this very old issue.