rustc query cycle handler panic

[fe3dback]

It is an invalid data structure (because it is recursive), and the complier can't know size on compile time.
But compiler panic is unexpected here.

Code

use brg_core::prelude::{Chunk, V2};

#[derive(Default, Copy, Clone)]
pub struct LodQuadTree {
    pos:   V2,
    size:  V2,
    len:   u32,
    child: Option<[LodQuadTree; 4]>, // problem on this line (recursive)
}

Meta

rustc --version --verbose:

rustc 1.86.0-nightly (f85c6de55 2025-01-26)
binary: rustc
commit-hash: f85c6de55206dbee5ffedfd821df1503a7b92346
commit-date: 2025-01-26
host: x86_64-unknown-linux-gnu
release: 1.86.0-nightly
LLVM version: 19.1.7

Error output

thread 'rustc query cycle handler' panicked at compiler/rustc_query_system/src/query/job.rs:502:9:
deadlock detected as we're unable to find a query cycle to break
current query map:
{}
stack backtrace:
   0:     0x7adb02bb1625 - std::backtrace::Backtrace::create::h016cd0347bc39098
   1:     0x7adb00f8e6f5 - std::backtrace::Backtrace::force_capture::h90cd71109775fcb3
   2:     0x7adb0015b864 - std[cc940dec3ff43b12]::panicking::update_hook::<alloc[5f7a888829935c2b]::boxed::Box<rustc_driver_impl[af2bdb3744899392]::install_ice_hook::{closure#1}>>::{closure#0}
   3:     0x7adb00fa7073 - std::panicking::rust_panic_with_hook::hbfeeff1ab3569ba1
   4:     0x7adb00fa6d6a - std::panicking::begin_panic_handler::{{closure}}::h32c93c4f5d28ab99
   5:     0x7adb00fa46e9 - std::sys::backtrace::__rust_end_short_backtrace::h1884c239824d44f7
   6:     0x7adb00fa6a2d - rust_begin_unwind
   7:     0x7adafdc39bd0 - core::panicking::panic_fmt::he58927c3c03479ba
   8:     0x7adb00b9dcba - rustc_query_system[b5c6449b7ccd2566]::query::job::break_query_cycles
   9:     0x7adb001517dc - std[cc940dec3ff43b12]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[d0d5d02e7a56d74f]::util::run_in_thread_pool_with_globals<rustc_interface[d0d5d02e7a56d74f]::interface::run_compiler<(), rustc_driver_impl[af2bdb3744899392]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#2}::{closure#1}, ()>
  10:     0x7adb00162e98 - <<std[cc940dec3ff43b12]::thread::Builder>::spawn_unchecked_<rustc_interface[d0d5d02e7a56d74f]::util::run_in_thread_pool_with_globals<rustc_interface[d0d5d02e7a56d74f]::interface::run_compiler<(), rustc_driver_impl[af2bdb3744899392]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#2}::{closure#1}, ()>::{closure#1} as core[c1de5c9ad145c0db]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  11:     0x7adb0266832b - std::sys::pal::unix::thread::Thread::new::thread_start::hb22e947f5885a296
  12:     0x7adafc69ca94 - start_thread
                               at ./nptl/pthread_create.c:447:8
  13:     0x7adafc729c3c - clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:78:0
  14:                0x0 - <unknown>


rustc version: 1.86.0-nightly (f85c6de55 2025-01-26)
platform: x86_64-unknown-linux-gnu

[compiler-errors]

Can you share more information about how you're invoking the Rust compiler? Are you passing any -Z flags perhaps?

[fe3dback]

yes, forgot to write about custom config

.cargo/config.toml

[target.x86_64-unknown-linux-gnu]
linker = "clang"
rustflags = [
    "-C",
    # fast unstable linker
    "link-arg=-fuse-ld=mold",
    # (Nightly) Make the current crate share its generic instantiations
    "-Zshare-generics=y",
    "-Zthreads=0",
]

[unstable]
codegen-backend = true

[profile.dev]
codegen-backend = "cranelift"

[profile.dev.package."*"]
codegen-backend = "llvm"

[lqd]

Does reproducing this require code from brg_core?

[fe3dback]

no, it is reproduced in minimum main.rs:

pub struct LodQuadTree {
    child: Option<[LodQuadTree; 4]>, // problem on this line (recursive)
}

fn main() {
    println!("hello world")
}

[lqd]

I personally can't reproduce this.

Aaaaaaaaaaaaaaaaaaaaaaaaaaaaah I know what this is. It's the driver queries with -Zthreads>1.

[lqd]

Summary: this is fixed on nightly.

Whenever you're using nightly, the error messages mention to update and check again, for that very reason.

note: please make sure that you have updated to the latest nightly

This is a duplicate of #135870 and was already fixed by #135988. I've verified that updating your toolchain to at least nightly-2025-01-28 should prevent this issue from appearing in your project. Feel free to reopen if it happens again.

Thanks for opening an issue!

[fe3dback]

confirm, after update to latest nightly, I get correct error message error[E0072]: recursive type LodQuadTree has infinite size, and compiler no longer panics.