Two test cases for incorrect region inference

[brson]

I came up with these two similar test cases for region-related ICEs. They both have to do with JsonDeserializer's interior pointer.

pub trait Deserializable<D> {
    static fn deserialize(&self, d: &D) -> self;
}

pub impl<D> int: Deserializable<D> {
    static fn deserialize(&self, _d: &D) -> int { fail }
}

struct JsonDeserializer {
    stack: &int,
}

impl JsonDeserializer {
}

trait Unflattenator<T> {
    fn unflatten(&self) -> T;
}

struct DeserializingUnflattenator<D, T: Deserializable<D>> {
    bogus: ()
}

fn from_reader<D>() -> D { fail }

fn unflatten<D, T: Deserializable<D>>(_s: &DeserializingUnflattenator<D, T>) -> T {
    let deser: &D = &from_reader();
    deserialize(deser)
}

fn m(_t: &r/int) {
    let unflat: DeserializingUnflattenator<JsonDeserializer, int> = DeserializingUnflattenator { bogus: () };
    unflatten(&unflat);
}

fn main() {
}

note: cannot encode region variables lifetime re_infer(ReVar(RegionVid(0)))
error: internal compiler error: Cannot encode region variables

pub trait Deserializable<D> {
    static fn deserialize(&self, d: &D) -> self;
}

pub impl<D> int: Deserializable<D> {
    static fn deserialize(&self, d: &D) -> int { fail }
}

struct JsonDeserializer {
    stack: &int,
}

impl JsonDeserializer {
}

trait Unflattenator<T> {
    fn unflatten(&self) -> T;
}

struct DeserializingUnflattenator<D, T: Deserializable<D>> {
    bogus: ()
}

fn from_reader<D>() -> D { fail }

fn unflatten<D, T: Deserializable<D>>() -> T {
    let deser: &D = &from_reader();
    deserialize(deser)
}

fn m(foo: &r/int) {
    unflatten::<JsonDeserializer, int>();
}

fn main() {
}

/home/brian/dev/rust2/src/test/run-pass/flatpipe-encode2.rs:32:16: 32:32 error: Unconstrained region variable #0
/home/brian/dev/rust2/src/test/run-pass/flatpipe-encode2.rs:32     unflatten::<JsonDeserializer, int>();

[erickt]

@nikomatsakis: I bisected my Cannot encode region variables bug and it seems to match up with issue. I thought this bug was recent, but I just did a big bisection and found it's been present since 2012-10-23, in ab89b5c, where I made the serialization traits take type parameters. So the JSON decoder has been busted for a couple months now because we didn't have a proper test case. I'm guessing this bug is from region inference not properly working with trait type parameters.

[erickt]

Oh and here's the test case I used to reduce the bug down to that commit:

extern mod std;
use std::json;
use std::serialization::{Deserializable, deserialize};

fn main() {
    do io::with_str_reader("[1]") |rdr| {
        let deser = result::unwrap(json::Deserializer(rdr));
        let x: ~[int] = deserialize(&deser);
        io::println(fmt!("%?", x));
    }
}

[erickt]

Here's the modern version of the test case:

extern mod std;
use std::json;
use std::serialize;

fn main() {
    let json = json::from_str("[1]").unwrap();
    let _x: ~[int] = serialize::Decodable::decode(&json::Decoder(json));
}