From 045ec8f2cf69533fe0b76c392acae2cd86b3a3ff Mon Sep 17 00:00:00 2001
From: Leo Singer <leo.singer@ligo.org>
Date: Thu, 27 Feb 2020 14:12:39 -0500
Subject: [PATCH] Fix LaTeX error due to labels that become empty in
 simplify_labels

Fixes #8004.
---
 CHANGES.rst                                   |  3 ++
 .../visualization/wcsaxes/tests/test_misc.py  | 40 ++++++++++++++++++-
 astropy/visualization/wcsaxes/ticklabels.py   |  2 +
 3 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index 080564895571..7c61313232be 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -488,6 +488,9 @@ astropy.visualization
   maximum when there are less then ``min_npixels`` in the input array.
   [#9913]
 
+- Fix a bug in simplifying axis labels that affected non-rectangular frames.
+  [#8004, #9991]
+
 astropy.wcs
 ^^^^^^^^^^^
 
diff --git a/astropy/visualization/wcsaxes/tests/test_misc.py b/astropy/visualization/wcsaxes/tests/test_misc.py
index 3c10e27f94c1..8b5315bd96a9 100644
--- a/astropy/visualization/wcsaxes/tests/test_misc.py
+++ b/astropy/visualization/wcsaxes/tests/test_misc.py
@@ -18,7 +18,8 @@
 from astropy.tests.image_tests import ignore_matplotlibrc
 
 from astropy.visualization.wcsaxes.core import WCSAxes
-from astropy.visualization.wcsaxes.frame import RectangularFrame, RectangularFrame1D
+from astropy.visualization.wcsaxes.frame import (
+    EllipticalFrame, RectangularFrame, RectangularFrame1D)
 from astropy.visualization.wcsaxes.utils import get_coord_meta
 from astropy.visualization.wcsaxes.transforms import CurvedTransform
 
@@ -446,3 +447,40 @@ def test_time_wcs(time_spectral_wcs_2d):
     # with a time axis.
 
     plt.subplot(projection=time_spectral_wcs_2d)
+
+
+@pytest.mark.skipif('MATPLOTLIB_LT_21')
+@ignore_matplotlibrc
+def test_simplify_labels_usetex(tmpdir):
+    """Regression test for https://github.com/astropy/astropy/issues/8004."""
+    plt.rc('text', usetex=True)
+
+    header = {
+        'NAXIS': 2,
+        'NAXIS1': 360,
+        'NAXIS2': 180,
+        'CRPIX1': 180.5,
+        'CRPIX2': 90.5,
+        'CRVAL1': 180.0,
+        'CRVAL2': 0.0,
+        'CDELT1': -2 * np.sqrt(2) / np.pi,
+        'CDELT2': 2 * np.sqrt(2) / np.pi,
+        'CTYPE1': 'RA---MOL',
+        'CTYPE2': 'DEC--MOL',
+        'RADESYS': 'ICRS'}
+
+    wcs = WCS(header)
+    fig, ax = plt.subplots(
+        subplot_kw=dict(frame_class=EllipticalFrame, projection=wcs))
+    ax.set_xlim(-0.5, header['NAXIS1'] - 0.5)
+    ax.set_ylim(-0.5, header['NAXIS2'] - 0.5)
+    ax.coords[0].set_ticklabel(exclude_overlapping=True)
+    ax.coords[1].set_ticklabel(exclude_overlapping=True)
+    ax.coords[0].set_ticks(spacing=45 * u.deg)
+    ax.coords[1].set_ticks(spacing=30 * u.deg)
+    ax.grid()
+
+    if not matplotlib.checkdep_usetex(True):
+        pytest.skip('TeX is not available')
+
+    fig.savefig(tmpdir / 'plot.png')
diff --git a/astropy/visualization/wcsaxes/ticklabels.py b/astropy/visualization/wcsaxes/ticklabels.py
index d515f5abd44c..d910722fd345 100644
--- a/astropy/visualization/wcsaxes/ticklabels.py
+++ b/astropy/visualization/wcsaxes/ticklabels.py
@@ -93,6 +93,8 @@ def simplify_labels(self):
                     self.text[axis][i] = self.text[axis][i][start:]
                     if starts_dollar:
                         self.text[axis][i] = '$' + self.text[axis][i]
+                if self.text[axis][i] == '$$':
+                    self.text[axis][i] = ''
 
     def set_pad(self, value):
         self._pad = value