ICE when working with infinitely nesting types and ?-operator

dastbe commented 2 years ago

Code

I've hacked it down from an advent of code solution. When

    let version = extend_number(0, itr, 3)?;
    let type_id = extend_number(0, itr, 3)?;

is replaced with u32 literals the compiler emits a (correct) compilation error due to infinitely nesting types.

use std::vec::Vec;
use std::iter::Peekable;

pub fn main() {
    let packet = decode(vec![1,0,1,0]);
}

pub fn decode(bitstream: Vec<u64>) -> Packet {
    let mut bitstream_itr = bitstream.into_iter().peekable();
    return match decode_packet(&mut bitstream_itr) {
        Some(p) => p,
        None    => panic!("expected outer packet"),
    }
}

pub fn decode_packets<I: Iterator<Item = u64>>(itr: &mut Peekable<I>) -> Vec<Packet> {
    let mut res = Vec::new();
    loop {
        match decode_packet(itr) {
            Some(p) => { res.push(p); },
            None    => break
        }
    }

    return res;
}

pub fn decode_packet<I: Iterator<Item = u64>>(itr: &mut Peekable<I>) -> Option<Packet> {
    // get version digits
    let version = extend_number(0, itr, 3)?;
    let type_id = extend_number(0, itr, 3)?;
    return operator_packet(version, type_id, itr);
}

pub fn operator_packet<I: Iterator<Item = u64>>(version: u64, type_id: u64, itr: &mut Peekable<I>) -> Option<Packet> {
    let p = OperatorPacket {
        version: version,
        type_id: type_id,
        packets: decode_packets(&mut itr.take(0).peekable()),
    };

    return Some(Packet::Operator(p));
}

pub fn extend_number<I: Iterator<Item = u64>>(num: u64, itr: &mut Peekable<I>, take: u64) -> Option<u64> {
    let mut value = num;
    for _ in 0..take {
        value *= 2;
        value += itr.next()?;
    }

    return Some(value);
}

#[derive(Debug)]
pub enum Packet {
    Operator(OperatorPacket),
}

#[derive(Debug)]
pub struct OperatorPacket {
    version: u64,
    type_id: u64,
    packets: Vec<Packet>
}

Error output

thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', /Users/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/ena-0.14.0/src/snapshot_vec.rs:199:10
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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 1.59.0-nightly (db9d361a4 2021-11-28) running on aarch64-apple-darwin

note: compiler flags: -C embed-bitcode=no -C split-debuginfo=unpacked -C debuginfo=2 -C incremental --crate-type bin

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

query stack during panic:
#0 [is_copy_raw] computing whether `core::option::Option<core::option::Option<_>>` is `Copy`
#1 [needs_drop_raw] computing whether `core::option::Option<core::option::Option<_>>` needs drop
end of query stack
warning: `aoc-uh-oh` (bin "aoc-uh-oh") generated 4 warnings
error: could not compile `aoc-uh-oh`; 4 warnings emitted

Backtrace

``` stack backtrace: 0: _rust_begin_unwind 1: core::panicking::panic_fmt 2: core::panicking::panic_bounds_check 3: ::probe 4: ::probe_ty_var 5: ::fold_ty 6: <&rustc_middle::ty::list::List as rustc_middle::ty::fold::TypeFoldable>::fold_with:: 7: <&rustc_middle::ty::TyS as rustc_middle::ty::fold::TypeFoldable>::super_fold_with:: 8: <&rustc_middle::ty::list::List as rustc_middle::ty::fold::TypeFoldable>::fold_with:: 9: <&rustc_middle::ty::TyS as rustc_middle::ty::fold::TypeFoldable>::super_fold_with:: 10: <&rustc_middle::ty::list::List as rustc_middle::ty::fold::TypeFoldable>::fold_with:: 11: ::fold_with:: 12: ::canonicalize::> 13: ::evaluate_obligation 14: ::evaluate_obligation_no_overflow 15: rustc_trait_selection::traits::type_known_to_meet_bound_modulo_regions 16: ::enter:: 17: rustc_ty_utils::common_traits::is_copy_raw 18: >::with_task::, bool> 19: rustc_data_structures::stack::ensure_sufficient_stack::<(bool, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job, bool>::{closure#3}> 20: rustc_query_system::query::plumbing::try_execute_query::, bool>> 21: rustc_query_system::query::plumbing::get_query:: 22: ::is_copy_modulo_regions 23: rustc_ty_utils::needs_drop::needs_drop_raw 24: >::with_task::, bool> 25: rustc_data_structures::stack::ensure_sufficient_stack::<(bool, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job, bool>::{closure#3}> 26: rustc_query_system::query::plumbing::try_execute_query::, bool>> 27: rustc_query_system::query::plumbing::get_query:: 28: rustc_ty_utils::instance::inner_resolve_instance 29: rustc_ty_utils::instance::resolve_instance 30: ::with_deps::<>::with_task_impl)>, core::result::Result, rustc_errors::ErrorReported>>::{closure#0}, core::result::Result, rustc_errors::ErrorReported>> 31: >::with_task::)>, core::result::Result, rustc_errors::ErrorReported>> 32: rustc_data_structures::stack::ensure_sufficient_stack::<(core::result::Result, rustc_errors::ErrorReported>, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job)>, core::result::Result, rustc_errors::ErrorReported>>::{closure#3}> 33: rustc_query_system::query::plumbing::get_query:: 34: ::resolve_instance 35: ::resolve_opt_const_arg 36: ::resolve_drop_in_place 37: ::visit_terminator 38: rustc_monomorphize::collector::collect_neighbours 39: rustc_monomorphize::collector::collect_items_rec 40: rustc_monomorphize::collector::collect_items_rec 41: rustc_monomorphize::collector::collect_items_rec 42: rustc_monomorphize::collector::collect_items_rec 43: rustc_monomorphize::collector::collect_items_rec 44: rustc_monomorphize::collector::collect_items_rec 45: rustc_monomorphize::collector::collect_items_rec 46: rustc_monomorphize::collector::collect_items_rec 47: rustc_monomorphize::collector::collect_items_rec 48: rustc_monomorphize::collector::collect_items_rec 49: rustc_monomorphize::collector::collect_items_rec 50: rustc_monomorphize::collector::collect_items_rec 51: rustc_monomorphize::collector::collect_items_rec 52: rustc_monomorphize::collector::collect_items_rec 53: rustc_monomorphize::collector::collect_items_rec 54: rustc_monomorphize::collector::collect_items_rec 55: rustc_monomorphize::collector::collect_items_rec 56: rustc_monomorphize::collector::collect_items_rec 57: rustc_monomorphize::collector::collect_items_rec 58: rustc_monomorphize::collector::collect_items_rec 59: rustc_monomorphize::collector::collect_items_rec 60: rustc_monomorphize::collector::collect_items_rec 61: rustc_monomorphize::collector::collect_items_rec 62: rustc_monomorphize::collector::collect_items_rec 63: rustc_monomorphize::collector::collect_items_rec 64: rustc_monomorphize::collector::collect_items_rec 65: rustc_monomorphize::collector::collect_items_rec 66: rustc_monomorphize::collector::collect_items_rec 67: rustc_monomorphize::collector::collect_items_rec 68: rustc_monomorphize::collector::collect_items_rec 69: rustc_monomorphize::collector::collect_items_rec 70: rustc_monomorphize::collector::collect_items_rec 71: rustc_monomorphize::collector::collect_items_rec 72: rustc_monomorphize::collector::collect_items_rec 73: rustc_monomorphize::collector::collect_items_rec 74: rustc_monomorphize::collector::collect_items_rec 75: rustc_monomorphize::collector::collect_items_rec 76: rustc_monomorphize::collector::collect_items_rec 77: rustc_monomorphize::collector::collect_items_rec 78: rustc_monomorphize::collector::collect_items_rec 79: rustc_monomorphize::collector::collect_items_rec 80: rustc_monomorphize::collector::collect_items_rec 81: rustc_monomorphize::collector::collect_items_rec 82: rustc_monomorphize::collector::collect_items_rec 83: rustc_monomorphize::collector::collect_items_rec 84: rustc_monomorphize::collector::collect_items_rec 85: rustc_monomorphize::collector::collect_items_rec 86: rustc_monomorphize::collector::collect_items_rec 87: rustc_monomorphize::collector::collect_items_rec 88: rustc_monomorphize::collector::collect_items_rec 89: rustc_monomorphize::collector::collect_items_rec 90: rustc_monomorphize::collector::collect_items_rec 91: rustc_monomorphize::collector::collect_items_rec note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace. 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 1.59.0-nightly (db9d361a4 2021-11-28) running on aarch64-apple-darwin note: compiler flags: -C embed-bitcode=no -C split-debuginfo=unpacked -C debuginfo=2 -C incremental --crate-type bin note: some of the compiler flags provided by cargo are hidden query stack during panic: #0 [is_copy_raw] computing whether `core::option::Option>` is `Copy` #1 [needs_drop_raw] computing whether `core::option::Option>` needs drop #2 [resolve_instance] resolving instance `core::ptr::drop_in_place::>>` #3 [collect_and_partition_mono_items] collect_and_partition_mono_items end of query stack ```

Aaron1011 commented 2 years ago

We're incorrectly invoking resolve_instance with an inference car - this should never happen, but we seem to still have inference cars present during monomorphization.

I suspect that this is related to the overflow, and could be solved by skipping Instance::resolve and calling delay_span_bug when we encounter an unresolved inference variable.