Stack overflow when parsing deeply nested map

Reproduction:

fn main() {
    let _: Result<ron::Value, _> = ron::from_str(&"{".repeat(10_000));
}

Found by fuzzing, I'll make a distinct PR to add the fuzzer.

[juntyr]

serde_json 'gets around' this issue by setting an inner depth limit and checking against it: https://github.com/serde-rs/json/blob/379412b13875cfb2e440937c4508944d48ee6c96/src/de.rs#L1272-L1287. Given serde's recursive parser architecture, I'm not sure if something better than such a custom error message could be achieved.

[juntyr]

This issue is not with ron itself but with serde's recursive design. The serde_stacker crate provides a Serializer and Deserializer wrapper for users who want to parse highly recursive datastructures by dynamically growing the stack as needed.

[juntyr]

I closed this issue a bit prematurely - while the problem is fundamental to serde and serde_stacker can be used to alleviate the issue in many cases, in the end there has to be some limit or we crash. Hence, I think it is better to allow users to specify that limit explicitly in #420.