Handle parser stack overflows more gracefully

[MeGaGiGaGon]

Summary

Currently, if you have a file that causes a stack overflow in the parser ruff/ty will crash with the usual message thread 'main' (...) has overflowed its stack. It would be nice if there was a better/more clear error when that happens, to differentiate logic-based errors in ruff/ty from "your file is too big/complex" errors.

Version

ruff 0.14.14 (8b2e7b3 2026-01-22) / ty 0.0.14 (16597f5e2 2026-01-26)

[MichaReiser]

I think we should fix the parser instead. It shouldn't panic for any <= 4GB Python file.

This may require rewriting some recursive parsing to use loops or we can dynamically grow the stack size, using something like stacker

[MeGaGiGaGon]

I didn't suggest that initially since because in all the things I tried cpython's limits are set lower that where ruff/ty currently stack overflow, so all valid python should also still be covered. It would be cool though.

[samuelcolvin]

It's pretty easy to get a stack oveflow which is unfortunate for those of us using ruff to parase untrusted code.

Here's a simple MRE that works with main when run with cargo run --release -- 5000:

//! MRE: pure ruff_python_parser stack overflow on deeply nested parens.

use ruff_python_parser::parse_module;

fn main() {
    let depth: usize = std::env::args()
        .nth(1)
        .and_then(|s| s.parse().ok())
        .unwrap_or(2000);

    let mut code = String::with_capacity(depth * 2 + 1);
    for _ in 0..depth {
        code.push('(');
    }
    code.push('1');
    for _ in 0..depth {
        code.push(')');
    }

    println!("parsing expr with paren depth = {depth}, bytes = {}", code.len());
    match parse_module(&code) {
        Ok(_) => println!("parsed OK"),
        Err(e) => println!("parse error: {e}"),
    }
    println!("survived");
}