* Fix stack overflow on deeply-nested JSON in json.loads()
json.loads() on a deeply-nested array or object payload (e.g.
'[' * 50000 + ']' * 50000) overflowed the native Rust stack and
crashed the interpreter process with SIGSEGV. CPython raises
RecursionError on the same input via _Py_EnterRecursiveCall in
Modules/_json.c.
The recursion lives in the mutual call chain:
JsonScanner::parse_object / parse_array
-> JsonScanner::call_scan_once
-> JsonScanner::parse_object / parse_array
Every descent funnels through call_scan_once, so wrapping its body
with vm.with_recursion covers both '{' and '[' paths (and their
mixed nesting) with a single guard.
Before:
./rustpython -c "import json; json.loads('[' * 50000 + ']' * 50000)"
-> SIGSEGV (exit 139)
After:
-> RecursionError: maximum recursion depth exceeded while
decoding a JSON object from a string
Verified:
- extra_tests/snippets/stdlib_json.py: all assertions pass
(includes 3 new regression cases: array, object, alternating
nesting at depth 100000)
- cargo run -- -m test test_json: 214 passed, 0 regressed
(9 skipped, 13 expected failures, all pre-existing)
- depth 500000 no longer crashes (RecursionError)
- shallow parsing unchanged
* Enable test_highly_nested_objects_decoding
Per @ShaharNaveh's review on #7632: this test was previously marked
`@unittest.skip("TODO: RUSTPYTHON; crashes")` because json.loads
would SIGSEGV on the 500_000-deep input. The recursion-guard added
in this PR makes it raise RecursionError like CPython, so the skip
decorator can be removed.
$ cargo run -- -m unittest \
test.test_json.test_recursion.TestCRecursion.test_highly_nested_objects_decoding \
test.test_json.test_recursion.TestPyRecursion.test_highly_nested_objects_decoding
...
Ran 2 tests in 0.825s
OK
$ cargo run -- -m test test_json
Ran 214 tests (7 skipped, 13 expected failures) — all pass.
