[ICE]: Panic with recursive type + GAT

[douglas-raillard-arm]

Code

pub trait Functor
{
    type With<T>: Functor;
}

pub struct IdFunctor<T>(T);
impl<T> Functor for IdFunctor<T> {
    type With<T2> = IdFunctor<T2>;
}

impl<T> Functor for Vec<T> {
    type With<T2> = Vec<T2> ;
}


pub struct Compose<F1, F2, T>(F1::With<F2::With<T>>)
where
    F1: Functor + ?Sized,
    F2: Functor + ?Sized;

impl<F1, F2, T> Functor for Compose<F1, F2, T>
where
    F1: Functor + ?Sized,
    F2: Functor + ?Sized
{
    type With<T2> = F1::With<F2::With<T2>> ;
}

pub enum Value<F>
where
    F: Functor + ?Sized,
{
    SignedInt(*mut F::With<i64>),
    Array(*mut Value<Compose<F, Vec<()>, ()>>),

}

fn main() {
    let x: Value<IdFunctor<()>> = Value::SignedInt(&mut IdFunctor(1));
}

Affected release channels

• Previous Stable
• Current Stable
• Current Beta
• Current Nightly

Rust Version

Compiled on the playground so here is the info I could gather:

note: rustc 1.69.0-nightly (d7948c843 2023-01-26) running on x86_64-unknown-linux-gnu
note: compiler flags: --crate-type bin -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2
note: some of the compiler flags provided by cargo are hidden

Current error output

 
⣿
Standard Error

   Compiling playground v0.0.1 (/playground)
warning: unused variable: `x`
  --> src/main.rs:39:9
   |
39 |     let x: Value<IdFunctor<()>> = Value::SignedInt(&mut IdFunctor(1));
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`
   |
   = note: `#[warn(unused_variables)]` on by default

thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', /cargo/registry/src/github.com-1ecc6299db9ec823/ena-0.14.0

[...]

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.69.0-nightly (d7948c843 2023-01-26) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type bin -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [is_sized_raw] computing whether `_` is `Sized`
#1 [layout_of] computing layout of `*mut _`
#2 [layout_of] computing layout of `*mut <Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<IdFunctor<()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()> as Functor>::With<i64>`
#3 [layout_of] computing layout of `Value<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<Compose<IdFunctor<()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>, alloc::vec::Vec<()>, ()>>`
end of query stack
warning: `playground` (bin "playground") generated 1 warning (run `cargo fix --bin "playground"` to apply 1 suggestion)
error: could not compile `playground`; 1 warning emitted

Backtrace

Apologies for pastebin, but github rejects issues with more than 65536 char:
https://pastebin.com/jsEBz8MM

Anything else?

replacing this:

    SignedInt(*mut F::With<i64>),
[...]
    let x: Value<IdFunctor<()>> = Value::SignedInt(&mut IdFunctor(1));

By that:

    SignedInt(F::With<i64>),
[...]
    let x: Value<IdFunctor<()>> = Value::SignedInt(IdFunctor(1));

brings a "normal compiler error":

error[[E0275]](https://doc.rust-lang.org/nightly/error-index.html#E0275): overflow evaluating the requirement `Value<Compose<Compose<Compose<Compose<Compose<Compose<..., ..., ...>, ..., ...>, ..., ...>, ..., ...>, ..., ...>, ..., ...>>: Sized`
  |
  = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`playground`)

Which seems pretty consistent with the error encountered with the pointer:

#0 [is_sized_raw] computing whether `_` is `Sized`

[douglas-raillard-arm]

This came up while attempting to craft a Value type used for an interpreter that has a homogeneous array type. Being able to work with a type like that:

pub enum Value<F>
where
    F: Functor,
{
    SignedInt(F::With<i64>),
    Array(Box<Value<Compose<F, Vec<()>, ()>>>),

}

would allow "sharing" the tag between all the values in the array, without needing any unsafe code and without requiring boxing in the non-array case.

The code with pointers was a result of trying to get passed the Sized issue, where rustc is unable to prove that Compose<F1, F2, T> is Sized even when F1 is Sized and essentially Compose<F1, F2, ()> == F1<F2>`

[matthiaskrgr]

Seems be some kind of overflow while computing layout with -Cdebuginfo=2

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-medium

[apiraino]

bisection points to commit 65c53c3 cc: @bjorn3

searched nightlies: from nightly-2022-07-01 to nightly-2023-01-01
regressed nightly: nightly-2022-12-18
searched commit range: 9c07efe...0468a00
regressed commit: 65c53c3

bisected with cargo-bisect-rustc v0.6.5

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

$ cat test.sh
#!/bin/sh
rustc --crate-type bin -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2 main.rs

cargo bisect-rustc --start=2022-07-01 --end=2023-01-31 --script test.sh --regress ice 

Note that I bisected the issue setting --end=2023-01-31 because it seems that in latest nightly it does not reproduce anymore. Can you confirm @douglas-raillard-arm ?

[bjorn3]

How could that have caused this issue? That was a change in the linkage code, while this crash happens in typeck.

[apiraino]

Ok, after a second run I'll post a better bisection result.

So, the regression really started in fd815a5 cc @compiler-errors

searched nightlies: from nightly-2022-11-15 to nightly-2022-12-10
regressed nightly: nightly-2022-11-25
searched commit range: 70f8737...b3bc6bf
regressed commit: fd815a5

bisected with cargo-bisect-rustc v0.6.5

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --start=2022-11-15 --end=2022-12-10 --script test.sh 

As mentioned before, I could not reproduce in the latest nightly.

thanks @bjorn3 for the tip and sorry about the unneeded mention before!