From ba8980c9fe31a2b4f64094b3ada765a6ff4dea1e Mon Sep 17 00:00:00 2001
From: tfpf <19171016+tfpf@users.noreply.github.com>
Date: Mon, 22 Aug 2022 22:04:47 +0530
Subject: [PATCH 1/2] When glyph is not found in `cmr10`, substitute from
 `cmsy10`.

---
 lib/matplotlib/_mathtext.py | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
index 44bb5a9e8fd8..5cc2dc052ce1 100644
--- a/lib/matplotlib/_mathtext.py
+++ b/lib/matplotlib/_mathtext.py
@@ -475,6 +475,14 @@ class UnicodeFonts(TruetypeFonts):
     symbol can not be found in the font.
     """
 
+    # Some glyphs are not present in the `cmr10` font, and must be brought in
+    # from `cmsy10`. Map the Unicode indices of those glyphs to the indices at
+    # which they are found in `cmsy10`.
+    _cmr10_substitutions = {
+        0x00D7: 0x00A3,  # Multiplication sign.
+        0x2212: 0x00A1,  # Minus sign.
+    }
+
     def __init__(self, *args, **kwargs):
         # This must come first so the backend's owner is set correctly
         fallback_rc = mpl.rcParams['mathtext.fallback']
@@ -541,11 +549,11 @@ def _get_glyph(self, fontname, font_class, sym):
             found_symbol = False
             font = self._get_font(new_fontname)
             if font is not None:
-                if font.family_name == "cmr10" and uniindex == 0x2212:
-                    # minus sign exists in cmsy10 (not cmr10)
+                if (uniindex in self._cmr10_substitutions
+                        and font.family_name == "cmr10"):
                     font = get_font(
                         cbook._get_data_path("fonts/ttf/cmsy10.ttf"))
-                    uniindex = 0xa1
+                    uniindex = self._cmr10_substitutions[uniindex]
                 glyphindex = font.get_char_index(uniindex)
                 if glyphindex != 0:
                     found_symbol = True

From f53301d2db02708452e18618237b716595c3a803 Mon Sep 17 00:00:00 2001
From: tfpf <19171016+tfpf@users.noreply.github.com>
Date: Mon, 22 Aug 2022 23:20:11 +0530
Subject: [PATCH 2/2] Test that `cmr10` in Mathtext does not warn about missing
 `\times`.

---
 lib/matplotlib/tests/test_ticker.py | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/lib/matplotlib/tests/test_ticker.py b/lib/matplotlib/tests/test_ticker.py
index e91d3236020d..b474dfdd5eaa 100644
--- a/lib/matplotlib/tests/test_ticker.py
+++ b/lib/matplotlib/tests/test_ticker.py
@@ -1,6 +1,7 @@
 from contextlib import nullcontext
 import itertools
 import locale
+import logging
 import re
 
 import numpy as np
@@ -725,6 +726,24 @@ def test_mathtext_ticks(self):
             ax.set_xticks([-1, 0, 1])
             fig.canvas.draw()
 
+    def test_cmr10_substitutions(self, caplog):
+        mpl.rcParams.update({
+            'font.family': 'cmr10',
+            'mathtext.fontset': 'cm',
+            'axes.formatter.use_mathtext': True,
+        })
+
+        # Test that it does not log a warning about missing glyphs.
+        with caplog.at_level(logging.WARNING, logger='matplotlib.mathtext'):
+            fig, ax = plt.subplots()
+            ax.plot([-0.03, 0.05], [40, 0.05])
+            ax.set_yscale('log')
+            yticks = [0.02, 0.3, 4, 50]
+            formatter = mticker.LogFormatterSciNotation()
+            ax.set_yticks(yticks, map(formatter, yticks))
+            fig.canvas.draw()
+            assert not caplog.text
+
     def test_empty_locs(self):
         sf = mticker.ScalarFormatter()
         sf.set_locs([])