Merge pull request matplotlib#20235 from aitikgupta/warn-mathtext

Author: anntzer

lib/matplotlib/tests/test_ticker.py

@@ -577,6 +577,18 @@ def test_cursor_dummy_axis(self, data, expected):
         fmt = sf.format_data_short
         assert fmt(data) == expected
 
+    def test_mathtext_ticks(self):
+        mpl.rcParams.update({
+            'font.family': 'serif',
+            'font.serif': 'cmr10',
+            'axes.formatter.use_mathtext': False
+        })
+
+        with pytest.warns(UserWarning, match='cmr10 font should ideally'):
+            fig, ax = plt.subplots()
+            ax.set_xticks([-1, 0, 1])
+            fig.canvas.draw()
+
 
 class FakeAxis:
     """Allow Formatter to be called without having a "full" plot set up."""

lib/matplotlib/ticker.py

@@ -475,6 +475,22 @@ def __init__(self, useOffset=None, useMathText=None, useLocale=None):
         self._usetex = mpl.rcParams['text.usetex']
         if useMathText is None:
             useMathText = mpl.rcParams['axes.formatter.use_mathtext']
+            if useMathText is False:
+                try:
+                    ufont = mpl.font_manager.findfont(
+                        mpl.font_manager.FontProperties(
+                            mpl.rcParams["font.family"]
+                        ),
+                        fallback_to_default=False,
+                    )
+                except ValueError:
+                    ufont = None
+
+                if ufont == str(cbook._get_data_path("fonts/ttf/cmr10.ttf")):
+                    _api.warn_external(
+                        "cmr10 font should ideally be used with "
+                        "mathtext, set axes.formatter.use_mathtext to True"
+                    )
         self.set_useMathText(useMathText)
         self.orderOfMagnitude = 0
         self.format = ''