Bug report

Bug summary

If matplotlib.axes.Axes.indicate_inset is called without specifying the label kwarg, then it sets indicate_inset as a default value (as per the source). If it does so while mpl.rc('text', usetex=True) is set and also creating a legend, LaTeX attempts to typeset the label indicate_inset, but fails due to the unescaped underscore. A solution is to pass label='' to indicate_inset, which should possibly be the new default.

Code for reproduction

import matplotlib as mpl
import matplotlib.pyplot as plt
mpl.rc('text', usetex=True)

fig, ax = plt.subplots(1,1)
axins   = ax.inset_axes([0.25, 0.65, 0.3, 0.3])
ax.indicate_inset_zoom(axins)
ax.legend(loc='best')
plt.show()

Actual outcome
A typical long LaTeX callback list, the relevant snippets are:

.
.
.
  File "/usr/lib/python3/dist-packages/matplotlib/texmanager.py", line 310, in _run_checked_subprocess
    raise RuntimeError(
RuntimeError: latex was not able to process the following string:
b'indicate_inset'
.
.
.
! Missing $ inserted.
<inserted text> 
                $
l.14 ...{10.000000}{12.500000}{\sffamily indicate_
                                                  inset}
No pages of output.
.
.
.

Matplotlib version

• Operating system: Ubuntu 20.04.1LTS, kernel version 5.4.0-62-generic
• Matplotlib version 3.1.2
• Matplotlib backend TkAgg:
• Python version: 3.8.5
• Other libraries: irrelevant

python and matplotlib both installed from official ubuntu repositories