bpo-40334: PEP 617 implementation: New PEG parser for CPython (GH-19503)

Co-authored-by: Guido van Rossum <guido@python.org>
Co-authored-by: Lysandros Nikolaou <lisandrosnik@gmail.com>

Tools/peg_generator/scripts/find_max_nesting.py

@@ -0,0 +1,61 @@
+#!/usr/bin/env python3.8
+"""Find the maximum amount of nesting for an expression that can be parsed
+without causing a parse error.
+
+Starting at the INITIAL_NESTING_DEPTH, an expression containing n parenthesis
+around a 0 is generated then tested with both the C and Python parsers. We
+continue incrementing the number of parenthesis by 10 until both parsers have
+failed. As soon as a single parser fails, we stop testing that parser.
+
+The grammar file, initial nesting size, and amount by which the nested size is
+incremented on each success can be controlled by changing the GRAMMAR_FILE,
+INITIAL_NESTING_DEPTH, or NESTED_INCR_AMT variables.
+
+Usage: python -m scripts.find_max_nesting
+"""
+import os
+import sys
+from tempfile import TemporaryDirectory
+from pathlib import Path
+from typing import Any
+
+from _peg_parser import parse_string
+
+GRAMMAR_FILE = "data/python.gram"
+INITIAL_NESTING_DEPTH = 10
+NESTED_INCR_AMT = 10
+
+
+FAIL = "\033[91m"
+ENDC = "\033[0m"
+
+
+def check_nested_expr(nesting_depth: int) -> bool:
+    expr = f"{'(' * nesting_depth}0{')' * nesting_depth}"
+
+    try:
+        parse_string(expr)
+        print(f"Nesting depth of {nesting_depth} is successful")
+        return True
+    except Exception as err:
+        print(f"{FAIL}(Failed with nesting depth of {nesting_depth}{ENDC}")
+        print(f"{FAIL}\t{err}{ENDC}")
+        return False
+
+
+def main() -> None:
+    print(f"Testing {GRAMMAR_FILE} starting at nesting depth of {INITIAL_NESTING_DEPTH}...")
+
+    nesting_depth = INITIAL_NESTING_DEPTH
+    succeeded = True
+    while succeeded:
+        expr = f"{'(' * nesting_depth}0{')' * nesting_depth}"
+        if succeeded:
+            succeeded = check_nested_expr(nesting_depth)
+        nesting_depth += NESTED_INCR_AMT
+
+    sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()