gh-108179: Add error message for parser stack overflows (#108256)

Lib/test/test_syntax.py

@@ -2335,7 +2335,7 @@ while 1:
         source = "-" * 100000 + "4"
         for mode in ["exec", "eval", "single"]:
             with self.subTest(mode=mode):
-                with self.assertRaises(MemoryError):
+                with self.assertRaisesRegex(MemoryError, r"too complex"):
                     compile(source, "<string>", mode)
 
     @support.cpython_only

Parser/pegen.h

@@ -166,6 +166,8 @@ void *_PyPegen_raise_error_known_location(Parser *p, PyObject *errtype,
                                           Py_ssize_t end_lineno, Py_ssize_t end_col_offset,
                                           const char *errmsg, va_list va);
 void _Pypegen_set_syntax_error(Parser* p, Token* last_token);
+void _Pypegen_stack_overflow(Parser *p);
+
 Py_LOCAL_INLINE(void *)
 RAISE_ERROR_KNOWN_LOCATION(Parser *p, PyObject *errtype,
                            Py_ssize_t lineno, Py_ssize_t col_offset,

Parser/pegen_errors.c

@@ -454,3 +454,11 @@ _Pypegen_set_syntax_error(Parser* p, Token* last_token) {
     // generic SyntaxError we just raised if errors are found.
     _PyPegen_tokenize_full_source_to_check_for_errors(p);
 }
+
+void
+_Pypegen_stack_overflow(Parser *p)
+{
+    p->error_indicator = 1;
+    PyErr_SetString(PyExc_MemoryError,
+        "Parser stack overflowed - Python source too complex to parse");
+}

Tools/peg_generator/pegen/c_generator.py

@@ -375,8 +375,7 @@ class CParserGenerator(ParserGenerator, GrammarVisitor):
     def add_level(self) -> None:
         self.print("if (p->level++ == MAXSTACK) {")
         with self.indent():
-            self.print("p->error_indicator = 1;")
+            self.print("_Pypegen_stack_overflow(p);")
-            self.print("PyErr_NoMemory();")
         self.print("}")
 
     def remove_level(self) -> None: