Make pegen output error detection checks after loop body for '*' rules.

Currently, the pegen output produces this for '+' rules:

    if (_n == 0 || p->error_indicator) {
        PyMem_Free(_children);
        p->level--;
        return NULL;
    }

But for '*' rules, no check is done at all, (skipping the _n == 0 makes sesnse of course)

For '*' it's possible for an error to be raised when parsing children, and currently the parser
sets the error flag/exception but does not return NULL, so parent rules might not detect the
error appropriately, as in this code:

        if (
            (a = _PyPegen_expect_token(p, FSTRING_START))  // token='FSTRING_START'
            &&
            (b = _loop0_79_rule(p))  // fstring_middle*
            &&
            (c = _PyPegen_expect_token(p, FSTRING_END))  // token='FSTRING_END'
        )

In this example, _PyPegen_expect_token can raise a SyntaxWarning which trips a debug assert.

This change outputs the same p->error_indicator check for '*' rules as for '+' rules.

Author: stestagg

Lib/test/test_fstring.py

@@ -604,6 +604,19 @@ def test_concat_decode_failure_does_not_crash(self):
 '''
         assert_python_ok('-c', script)
 
+    def test_memoryerror_during_concat_does_not_crash(self):
+        # gh-153182: Recursion/Memory errors parsing f-strings should be properly unwound
+        # and the parser should not attempt to continue parsing after the error. (In this case,
+        # a SyntaxWarning will subsequently be raised for the invalid escape, triggering a debug assert
+        # from the existing Exception)
+        script = r'''
+try:
+    compile('(x""f"\\{0}"<' * 1276, "<test>", "exec")
+except MemoryError:
+    pass
+'''
+        assert_python_ok('-c', script)
+
     def test_literal(self):
         self.assertEqual(f'', '')
         self.assertEqual(f'a', 'a')

Misc/NEWS.d/next/Core_and_Builtins/2026-07-09-15-39-19.gh-issue-153437.Dj2sRs.rst

@@ -0,0 +1,2 @@
+Fix an issue where some grammar rules tried to continue parsing after an
+error