Bug report

Bug summary

Use of \textrm latex in Cairo backend raises an exception

Code for reproduction

import matplotlib as mpl
import matplotlib.pyplot as plt

mpl.use('Cairo')
mpl.rc('text', usetex=True)

fig, ax = plt.subplots()

ax.set_xlabel(r'$x [\textrm{cm}]$')
ax.scatter([1, 2], [1, 2], marker='o')
fig.savefig('test-cairo.png')

Raises an exception

ValueError:
x [\textrm{cm}]
^ 
Unknown symbol: \textrm, found '\'  (at char 3), (line:1, col:4) 

Expected outcome

The textrm should work to produce rm text. For reference, this works fine in the Agg backend.

Matplotlib version

• Operating system: linux ubuntu
• Matplotlib version: 3.2.2
• Matplotlib backend: Cairo
• Python version: 3.7.6

Installed with conda