Bokeh Spacer sets height to one pixel with scale_width set

ALL software version info (bokeh, python, OS, browser, any other relevant packages)

bokeh: 0.12.15 python: 3.6.4 OS: Mac OS 10.12.6 browser: Google Chrome 65.0.3325.181 (Official Build) (64-bit)

Description of expected behavior and the observed behavior

I would expect to see a moderate amount of vertical separation between widgets, keeping the width/height ratio constant. However when I inspect the location the element should be, I see that it has a height of 1 pixel, regardless of the aspect ratio. I did not have this issue when putting a Spacer in a row. Putting the plot in the column too and skipping the row does not fix the problem.

Complete, minimal, self-contained example code that reproduces the issue

I modified the sliders.py example code to put the widgets in two separate boxes, then grouped them and a spacer in a column.

import numpy as np

from bokeh.io import curdoc
from bokeh.layouts import row, column, widgetbox, Spacer
from bokeh.models import ColumnDataSource
from bokeh.models.widgets import Slider, TextInput
from bokeh.plotting import figure

# Set up data
N = 200
x = np.linspace(0, 4*np.pi, N)
y = np.sin(x)
source = ColumnDataSource(data=dict(x=x, y=y))


# Set up plot
plot = figure(plot_height=400, plot_width=400, title="my sine wave",
              tools="crosshair,pan,reset,save,wheel_zoom",
              x_range=[0, 4*np.pi], y_range=[-2.5, 2.5])

plot.line('x', 'y', source=source, line_width=3, line_alpha=0.6)


# Set up widgets
text = TextInput(title="title", value='my sine wave')
offset = Slider(title="offset", value=0.0, start=-5.0, end=5.0, step=0.1)
amplitude = Slider(title="amplitude", value=1.0, start=-5.0, end=5.0, step=0.1)
phase = Slider(title="phase", value=0.0, start=0.0, end=2*np.pi)
freq = Slider(title="frequency", value=1.0, start=0.1, end=5.1, step=0.1)


# Set up callbacks
def update_title(attrname, old, new):
    plot.title.text = text.value

text.on_change('value', update_title)

def update_data(attrname, old, new):

    # Get the current slider values
    a = amplitude.value
    b = offset.value
    w = phase.value
    k = freq.value

    # Generate the new curve
    x = np.linspace(0, 4*np.pi, N)
    y = a*np.sin(k*x + w) + b

    source.data = dict(x=x, y=y)

for w in [offset, amplitude, phase, freq]:
    w.on_change('value', update_data)


# Set up layouts and add to document
##### BEGIN RELEVANT SECTION #####
input1 = widgetbox(text, offset)
input2 = widgetbox(amplitude, phase, freq)
inputs = column(input1, 
              Spacer(width=400, height=400, sizing_mode='scale_width'),
              input2, sizing_mode='scale_width')
##### END RELEVANT SECTION #####

curdoc().add_root(row(inputs, plot, sizing_mode='scale_width'))
curdoc().title = "Sliders"

Screenshots or screencasts of the bug in action

[bryevdv]

This appears to be fixed by #8085:

however @mattpap it appears Spacer was removed from bokeh.layouts, we should restore this transitive import from bokeh.models.layouts

[mattpap]

Using Div may serve as a temporary workaround, however, this solution may not work as expected in newer versions of bokeh. Currently this works, because empty Div has intrinsic padding, which seems to be a bug on its own.