Compiler panic when using recursive enums

[eternalfrustation]

Apparently, using enums which recursively reference themselves will result in a compiler panic

Below is a minimal enum that demonstrates this

Code

#[derive(Debug, Clone)]
pub enum DocAST {
    Line(DocAST),
    Text(String),
    Multi(Vec<DocAST>),
}

Meta

rustc --version --verbose:

rustc 1.85.0-nightly (d117b7f21 2024-12-31)
binary: rustc
commit-hash: d117b7f211835282b3b177dc64245fff0327c04c
commit-date: 2024-12-31
host: x86_64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.6

Error output

thread 'rustc query cycle handler' panicked at compiler/rustc_query_system/src/query/job.rs:504:9:
deadlock detected as we're unable to find a query cycle to break
current query map:
{"reason":"compiler-message","package_id":"path+file:///myprojects/rascii#0.1.0","manifest_path":"/myprojects/rascii/Cargo.toml","target":{"kind":["bin"],"crate_types":["bin"],"name":"rascii","src_path":"/myprojects/rascii/src/main.rs","edition":"2024","doc":true,"doctest":false,"test":true},"message":{}}
stack backtrace:
   0:     0x7ff77bad056a - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h3bfd73294bb40f7b
   1:     0x7ff77c213426 - core::fmt::write::hdcaca49087f51fc7
   2:     0x7ff77d13bcd1 - std::io::Write::write_fmt::h111e1637c3334990
   3:     0x7ff77bad03c2 - std::sys::backtrace::BacktraceLock::print::hc3646ef95a493c1e
   4:     0x7ff77bad28c9 - std::panicking::default_hook::{{closure}}::h4b5403c3b4e26604
   5:     0x7ff77bad2712 - std::panicking::default_hook::ha8ce32ac4bb77893
   6:     0x7ff77ac3dac8 - std[b0d549a58380ee12]::panicking::update_hook::<alloc[3e6ca5e693a94b55]::boxed::Box<rustc_driver_impl[3d9a82418e2383aa]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7ff77bad3083 - std::panicking::rust_panic_with_hook::h8585f3a7d0c05184
   8:     0x7ff77bad2d7a - std::panicking::begin_panic_handler::{{closure}}::h4ba34aed5dca5a84
   9:     0x7ff77bad0a19 - std::sys::backtrace::__rust_end_short_backtrace::h85d965d23ad807f9
  10:     0x7ff77bad2a3d - rust_begin_unwind
  11:     0x7ff77879df90 - core::panicking::panic_fmt::he33b64161001a34b
  12:     0x7ff77b67c37a - rustc_query_system[89d8cdfdd921bf80]::query::job::break_query_cycles
  13:     0x7ff77ac3438c - std[b0d549a58380ee12]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[5daad5fca9910f79]::util::run_in_thread_pool_with_globals<rustc_interface[5daad5fca9910f79]::interface::run_compiler<(), rustc_driver_impl[3d9a82418e2383aa]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#2}::{closure#1}, ()>
  14:     0x7ff77ac42b84 - <<std[b0d549a58380ee12]::thread::Builder>::spawn_unchecked_<rustc_interface[5daad5fca9910f79]::util::run_in_thread_pool_with_globals<rustc_interface[5daad5fca9910f79]::interface::run_compiler<(), rustc_driver_impl[3d9a82418e2383aa]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#2}::{closure#1}, ()>::{closure#1} as core[d51f785d25e19ba0]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  15:     0x7ff77d10f2c1 - std::sys::pal::unix::thread::Thread::new::thread_start::h9639e0dd1625826a
  16:     0x7ff7774b7f58 - <unknown>
  17:     0x7ff77752a5cc - <unknown>
  18:                0x0 - <unknown>

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

note: please attach the file at `/myprojects/rascii/rustc-ice-2025-02-10T11_25_26-27322.txt` to your bug report

note: compiler flags: --crate-type bin -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED] -C target-cpu=native -C link-arg=-fuse-ld=lld -Z threads=8

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

query stack during panic:
end of query stack
query cycle handler thread panicked, aborting process
sccache: Compile terminated by signal 6
error: could not compile `rascii` (bin "rascii")

Caused by:
  process didn't exit successfully: `sccache /home/sandy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc --crate-name rascii --edition=2024 src/main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=119 --crate-type bin --emit=dep-info,metadata -C embed-bitcode=no -C debuginfo=2 --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values())' -C metadata=782e36cd0d04c0c9 -C extra-filename=-8509920159b569fe --out-dir /myprojects/rascii/target/debug/deps -C incremental=/myprojects/rascii/target/debug/incremental -L dependency=/myprojects/rascii/target/debug/deps -C target-cpu=native -C link-arg=-fuse-ld=lld -Z threads=8` (exit status: 2)

Backtrace

thread 'rustc query cycle handler' panicked at compiler/rustc_query_system/src/query/job.rs:504:9:
deadlock detected as we're unable to find a query cycle to break
current query map:
{"reason":"compiler-message","package_id":"path+file:///myprojects/rascii#0.1.0","manifest_path":"/myprojects/rascii/Cargo.toml","target":{"kind":["bin"],"crate_types":["bin"],"name":"rascii","src_path":"/myprojects/rascii/src/main.rs","edition":"2024","doc":true,"doctest":false,"test":true},"message":{}}
stack backtrace:
   0:     0x7f45234d056a - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h3bfd73294bb40f7b
   1:     0x7f4523c13426 - core::fmt::write::hdcaca49087f51fc7
   2:     0x7f4524b3bcd1 - std::io::Write::write_fmt::h111e1637c3334990
   3:     0x7f45234d03c2 - std::sys::backtrace::BacktraceLock::print::hc3646ef95a493c1e
   4:     0x7f45234d28c9 - std::panicking::default_hook::{{closure}}::h4b5403c3b4e26604
   5:     0x7f45234d2712 - std::panicking::default_hook::ha8ce32ac4bb77893
   6:     0x7f452263dac8 - std[b0d549a58380ee12]::panicking::update_hook::<alloc[3e6ca5e693a94b55]::boxed::Box<rustc_driver_impl[3d9a82418e2383aa]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7f45234d3083 - std::panicking::rust_panic_with_hook::h8585f3a7d0c05184
   8:     0x7f45234d2d7a - std::panicking::begin_panic_handler::{{closure}}::h4ba34aed5dca5a84
   9:     0x7f45234d0a19 - std::sys::backtrace::__rust_end_short_backtrace::h85d965d23ad807f9
  10:     0x7f45234d2a3d - rust_begin_unwind
  11:     0x7f452019df90 - core::panicking::panic_fmt::he33b64161001a34b
  12:     0x7f452307c37a - rustc_query_system[89d8cdfdd921bf80]::query::job::break_query_cycles
  13:     0x7f452263438c - std[b0d549a58380ee12]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[5daad5fca9910f79]::util::run_in_thread_pool_with_globals<rustc_interface[5daad5fca9910f79]::interface::run_compiler<(), rustc_driver_impl[3d9a82418e2383aa]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#2}::{closure#1}, ()>
  14:     0x7f4522642b84 - <<std[b0d549a58380ee12]::thread::Builder>::spawn_unchecked_<rustc_interface[5daad5fca9910f79]::util::run_in_thread_pool_with_globals<rustc_interface[5daad5fca9910f79]::interface::run_compiler<(), rustc_driver_impl[3d9a82418e2383aa]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#2}::{closure#1}, ()>::{closure#1} as core[d51f785d25e19ba0]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  15:     0x7f4524b0f2c1 - std::sys::pal::unix::thread::Thread::new::thread_start::h9639e0dd1625826a
  16:     0x7f451eeb7f58 - <unknown>
  17:     0x7f451ef2a5cc - <unknown>
  18:                0x0 - <unknown>

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

note: please attach the file at `/myprojects/rascii/rustc-ice-2025-02-10T11_27_43-27753.txt` to your bug report

note: compiler flags: --crate-type bin -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED] -C target-cpu=native -C link-arg=-fuse-ld=lld -Z threads=8

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

query stack during panic:
end of query stack
query cycle handler thread panicked, aborting process
sccache: Compile terminated by signal 6
error: could not compile `rascii` (bin "rascii")

Caused by:
  process didn't exit successfully: `sccache /home/sandy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc --crate-name rascii --edition=2024 src/main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=119 --crate-type bin --emit=dep-info,link -C embed-bitcode=no -C debuginfo=2 --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values())' -C metadata=8e36858a67266172 -C extra-filename=-3e25946fc2c85d6b --out-dir /myprojects/rascii/target/debug/deps -C incremental=/myprojects/rascii/target/debug/incremental -L dependency=/myprojects/rascii/target/debug/deps -C target-cpu=native -C link-arg=-fuse-ld=lld -Z threads=8` (exit status: 2)

rustc-ice-2025-02-10T11_27_43-27753.txt

[theemathas]

Seems similar to #136453

Updating your rust should fix this

[fee1-dead]

Please update your Rust version and report again if the issue persists. I am unable to reproduce this on the playground.