Add unclosed group to grammar

Co-authored-by: Kyle Sunden <git@ksunden.space>

Author: devRD

lib/matplotlib/_mathtext.py

@@ -1894,6 +1894,7 @@ 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"))
@@ -1942,6 +1943,7 @@ def csnames(group, names):
         p.token <<= (
             p.simple
             | p.auto_delim
+            | p.unclosed_group
             | p.unknown_symbol  # Must be last
         )
 
@@ -2251,6 +2253,9 @@ 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 []

lib/matplotlib/tests/test_mathtext.py

@@ -320,7 +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 end of text'),
+        (r'$a = {b$', r"Expected '}'"),
     ],
     ids=[
         'hspace without value',
@@ -349,7 +349,7 @@ def test_fontinfo():
         'double superscript',
         'double subscript',
         'super on sub without braces',
-        'math string with no closing braces'
+        'unclosed group'
     ]
 )
 def test_mathtext_exceptions(math, msg):