Properly use thin space after math text operator.

mpetroff · mpetroff · commit 42e9b974028c · 2020-07-11T19:19:31.000Z
A thin space should follow a math operator except when it is followed by something like a parenthesis or a bracket. This should fix issue #17852.
diff --git a/lib/matplotlib/mathtext.py b/lib/matplotlib/mathtext.py
@@ -2876,7 +2876,14 @@ def function(self, s, loc, toks):
         self.push_state()
         state = self.get_state()
         state.font = 'rm'
-        hlist = Hlist([Char(c, state) for c in toks[0]])
+        hlist_list = [Char(c, state) for c in toks[0]]
+        next_char = next((c for c in s[loc+len(toks[0])+1:] if c != ' '), '')
+        delimiters = self._left_delim | self._ambi_delim | self._right_delim
+        if (next_char not in delimiters and
+                toks[0] not in self._overunder_functions):
+            # Add thin space except when followed by parenthesis, bracket, etc.
+            hlist_list += [self._make_space(self._space_widths[r'\,'])]
+        hlist = Hlist(hlist_list)
         self.pop_state()
         hlist.function_name = toks[0]
         return hlist
diff --git a/lib/matplotlib/tests/test_mathtext.py b/lib/matplotlib/tests/test_mathtext.py
@@ -285,6 +285,18 @@ def test_spaces(fig_test, fig_ref):
     fig_ref.subplots().set_title(r"$1\/2\:3~4$")
 
 
+@check_figures_equal(extensions=["png"])
+def test_operator_space(fig_test, fig_ref):
+    fig_test.text(0.1, 0.1, r"$\log 6$")
+    fig_test.text(0.1, 0.2, r"$\log(6)$")
+    fig_test.text(0.1, 0.3, r"$\arcsin 6$")
+    fig_test.text(0.1, 0.4, r"$\arcsin|6|$")
+    fig_ref.text(0.1, 0.1, r"$\mathrm{log\,}6$")
+    fig_ref.text(0.1, 0.2, r"$\mathrm{log}(6)$")
+    fig_ref.text(0.1, 0.3, r"$\mathrm{arcsin\,}6$")
+    fig_ref.text(0.1, 0.4, r"$\mathrm{arcsin}|6|$")
+
+
 def test_mathtext_fallback_valid():
     for fallback in ['cm', 'stix', 'stixsans', 'None']:
         mpl.rcParams['mathtext.fallback'] = fallback
