Tabs width set on width of contents - truncating tabs

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

Python version      :  3.6.8 |Anaconda, Inc.| (default, Dec 29 2018, 19:04:46) 
IPython version     :  7.1.1
Tornado version     :  5.1.1
Bokeh version       :  1.1.0dev8
BokehJS static path :  /Users/jsignell/conda/envs/panel-dev/lib/python3.6/site-packages/bokeh/server/static
node.js version     :  v7.10.0
npm version         :  4.2.0

Description of expected behavior and the observed behavior

The width of the tabs seems to be set based on the width of the item inside the tab without taking the width of the title into account. The result is a truncated tabs object where you can’t click on the second tab ( because it isn’t visible).

I originally raised this as https://github.com/pyviz/panel/issues/284

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

from bokeh.models.widgets import Panel, Tabs, Button
from bokeh.io import output_notebook, show
from bokeh.plotting import figure

output_notebook()

tab1 = Panel(child=Button(label='+', width=30), title="This is a long title")
tab2 = Panel(child=Button(label='-', width=30), title="This is another long title")
tabs = Tabs(tabs=[ tab1, tab2 ])

show(tabs)

Screenshots or screencasts of the bug in action

[philippjfr]

I think what you want is an equal_header_width option (would need to find a better name) on tabs that ensures that the tab headers are all the same width.

[jsignell]

The width needs to be large enough to see the title of every tab. If possible the titles should have a max_width set to 100%/n_tabs and they should wrap or overflow.