matplotlib · ksunden · Aug 21, 2023 · Aug 21, 2023
diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
@@ -1936,6 +1936,7 @@ def csnames(group, names):
        p.function = csnames("name", self._function_names)

        p.group = p.start_group + ZeroOrMore(p.token)("group") + p.end_group
+        p.unclosed_group = (p.start_group + ZeroOrMore(p.token)("group") + StringEnd())

        p.frac  = cmd(r"\frac", p.required_group("num") + p.required_group("den"))
        p.dfrac = cmd(r"\dfrac", p.required_group("num") + p.required_group("den"))
@@ -1984,6 +1985,7 @@ def csnames(group, names):
        p.token <<= (
            p.simple
            | p.auto_delim
+            | p.unclosed_group
            | p.unknown_symbol  # Must be last
        )

@@ -2072,7 +2074,7 @@ def main(self, s, loc, toks):
        return [Hlist(toks)]

    def math_string(self, s, loc, toks):
-        return self._math_expression.parseString(toks[0][1:-1])
+        return self._math_expression.parseString(toks[0][1:-1], parseAll=True)

    def math(self, s, loc, toks):
        hlist = Hlist(toks)
@@ -2294,6 +2296,9 @@ def end_group(self, s, loc, toks):
        self.pop_state()
        return []

+    def unclosed_group(self, s, loc, toks):
+        raise ParseFatalException(s, len(s), "Expected '}'")
+
    def font(self, s, loc, toks):
        self.get_state().font = toks["font"]
        return []

diff --git a/lib/matplotlib/tests/test_mathtext.py b/lib/matplotlib/tests/test_mathtext.py
@@ -320,6 +320,7 @@ def test_fontinfo():
        (r'$a^2^2$', r'Double superscript'),
        (r'$a_2_2$', r'Double subscript'),
        (r'$a^2_a^2$', r'Double superscript'),
+        (r'$a = {b$', r"Expected '}'"),
    ],
    ids=[
        'hspace without value',
@@ -347,7 +348,8 @@ def test_fontinfo():
        'unknown symbol',
        'double superscript',
        'double subscript',
-        'super on sub without braces'
+        'super on sub without braces',
+        'unclosed group',
    ]
 )
 def test_mathtext_exceptions(math, msg):