internal compiler error: min_const_generics resolve check didn't stop compilation

[mareksom]

Code

src/main.rs

struct A<const M: u32> {}

struct B<const M: u32> {}

impl<const M: u32> B<M> {
  const M: u32 = M;
}

struct C<const M: u32> {
  a: A<{B::<1>::M}>,
}

fn main() {}

Cargo.toml

[package]
name = "bug"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]

Meta

rustc --version --verbose:

rustc 1.60.0 (7737e0b5c 2022-04-04)
binary: rustc
commit-hash: 7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c
commit-date: 2022-04-04
host: x86_64-unknown-linux-gnu
release: 1.60.0
LLVM version: 14.0.0

Error output

$ cargo build

   Compiling bug v0.1.0 (/home/mareksom/lab/bug)
warning: struct is never constructed: `A`
 --> src/main.rs:1:8
  |
1 | struct A<const M: u32> {}
  |        ^
  |
  = note: `#[warn(dead_code)]` on by default

warning: struct is never constructed: `B`
 --> src/main.rs:3:8
  |
3 | struct B<const M: u32> {}
  |        ^

warning: associated constant is never used: `M`
 --> src/main.rs:6:3
  |
6 |   const M: u32 = M;
  |   ^^^^^^^^^^^^^^^^^

warning: struct is never constructed: `C`
 --> src/main.rs:9:8
  |
9 | struct C<const M: u32> {
  |        ^

warning: Error finalizing incremental compilation session directory `/home/mareksom/lab/bug/target/debug/incremental/bug-3u769ve6liwcr/s-g9f1tqsdvi-1ke0t4i-working`: No such file or directory (os error 2)

error: internal compiler error: min_const_generics resolve check didn't stop compilation
  --> src/main.rs:10:9
   |
10 |   a: A<{B::<1>::M}>,
   |         ^^^^^^^^^
   |
   = note: delayed at compiler/rustc_resolve/src/lib.rs:2886:46

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', compiler/rustc_errors/src/lib.rs:1176:13
stack backtrace:
   0:     0x7f7a074f886d - std::backtrace_rs::backtrace::libunwind::trace::hee598835bc88d35b
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f7a074f886d - std::backtrace_rs::backtrace::trace_unsynchronized::h9cdc730ba5cf5d72
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f7a074f886d - std::sys_common::backtrace::_print_fmt::h75aeaf7ed30e43fa
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/sys_common/backtrace.rs:66:5
   3:     0x7f7a074f886d - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h606862f787600875
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/sys_common/backtrace.rs:45:22
   4:     0x7f7a075584ec - core::fmt::write::he803f0f418caf762
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/core/src/fmt/mod.rs:1190:17
   5:     0x7f7a074e8a98 - std::io::Write::write_fmt::h70bc45872f37e7bb
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/io/mod.rs:1657:15
   6:     0x7f7a074fc847 - std::sys_common::backtrace::_print::h64d038cf8ac3e13e
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/sys_common/backtrace.rs:48:5
   7:     0x7f7a074fc847 - std::sys_common::backtrace::print::h359300b4a7fccf65
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/sys_common/backtrace.rs:35:9
   8:     0x7f7a074fc847 - std::panicking::default_hook::{{closure}}::hf51be35e2f510149
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/panicking.rs:295:22
   9:     0x7f7a074fc510 - std::panicking::default_hook::h03ca0f22e1d2d25e
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/panicking.rs:314:9
  10:     0x7f7a07c882c1 - rustc_driver[6eeb127b85fe99ac]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7f7a074fd124 - std::panicking::rust_panic_with_hook::h3b7380e99b825b63
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/panicking.rs:702:17
  12:     0x7f7a074fcdd7 - std::panicking::begin_panic_handler::{{closure}}::h8e849d0710154ce0
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/panicking.rs:588:13
  13:     0x7f7a074f8d34 - std::sys_common::backtrace::__rust_end_short_backtrace::hedcdaddbd4c46cc5
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/sys_common/backtrace.rs:138:18
  14:     0x7f7a074fcae9 - rust_begin_unwind
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/panicking.rs:584:5
  15:     0x7f7a074c5863 - core::panicking::panic_fmt::he1bbc7336d49a357
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/core/src/panicking.rs:143:14
  16:     0x7f7a08d7133c - core[2734bb1f7d9ec6a5]::panicking::panic_display::<&str>
  17:     0x7f7a0a3c831d - <rustc_errors[bd800fb2a5e0b9f5]::HandlerInner>::flush_delayed
  18:     0x7f7a0a3c677a - <rustc_errors[bd800fb2a5e0b9f5]::HandlerInner as core[2734bb1f7d9ec6a5]::ops::drop::Drop>::drop
  19:     0x7f7a09ae7bb6 - core[2734bb1f7d9ec6a5]::ptr::drop_in_place::<rustc_session[95a8f1c94d15e5dc]::parse::ParseSess>
  20:     0x7f7a09aea45a - <alloc[9a009599db7253ec]::rc::Rc<rustc_session[95a8f1c94d15e5dc]::session::Session> as core[2734bb1f7d9ec6a5]::ops::drop::Drop>::drop
  21:     0x7f7a09acf2ec - core[2734bb1f7d9ec6a5]::ptr::drop_in_place::<rustc_interface[afc566840a941718]::interface::Compiler>
  22:     0x7f7a09ad7f1e - rustc_interface[afc566840a941718]::interface::create_compiler_and_run::<core[2734bb1f7d9ec6a5]::result::Result<(), rustc_errors[bd800fb2a5e0b9f5]::ErrorReported>, rustc_driver[6eeb127b85fe99ac]::run_compi
ler::{closure#1}>
  23:     0x7f7a09abd134 - std[cd3cf6af28dff6de]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[afc566840a941718]::util::run_in_thread_pool_with_globals<rustc_interface[afc566840a941718]::interface::run_comp
iler<core[2734bb1f7d9ec6a5]::result::Result<(), rustc_errors[bd800fb2a5e0b9f5]::ErrorReported>, rustc_driver[6eeb127b85fe99ac]::run_compiler::{closure#1}>::{closure#0}, core[2734bb1f7d9ec6a5]::result::Result<(), rustc_errors[bd800f
b2a5e0b9f5]::ErrorReported>>::{closure#0}, core[2734bb1f7d9ec6a5]::result::Result<(), rustc_errors[bd800fb2a5e0b9f5]::ErrorReported>>
  24:     0x7f7a09af03e9 - <<std[cd3cf6af28dff6de]::thread::Builder>::spawn_unchecked_<rustc_interface[afc566840a941718]::util::run_in_thread_pool_with_globals<rustc_interface[afc566840a941718]::interface::run_compiler<core[2734bb1
f7d9ec6a5]::result::Result<(), rustc_errors[bd800fb2a5e0b9f5]::ErrorReported>, rustc_driver[6eeb127b85fe99ac]::run_compiler::{closure#1}>::{closure#0}, core[2734bb1f7d9ec6a5]::result::Result<(), rustc_errors[bd800fb2a5e0b9f5]::Erro
rReported>>::{closure#0}, core[2734bb1f7d9ec6a5]::result::Result<(), rustc_errors[bd800fb2a5e0b9f5]::ErrorReported>>::{closure#1} as core[2734bb1f7d9ec6a5]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  25:     0x7f7a07508d03 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hf70ac038171e3e1a
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/alloc/src/boxed.rs:1853:9
  26:     0x7f7a07508d03 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::he6690128792365ad
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/alloc/src/boxed.rs:1853:9
  27:     0x7f7a07508d03 - std::sys::unix::thread::Thread::new::thread_start::ha07928d93d5a5ec9
                               at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/sys/unix/thread.rs:108:17
  28:     0x7f7a0741d609 - start_thread
                               at /build/glibc-sMfBJT/glibc-2.31/nptl/pthread_create.c:477:8
  29:     0x7f7a07336163 - clone
  30:                0x0 - <unknown>

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 1.60.0 (7737e0b5c 2022-04-04) running on x86_64-unknown-linux-gnu

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

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

query stack during panic:
end of query stack
warning: `bug` (bin "bug") generated 5 warnings
error: could not compile `bug`; 5 warnings emitted

Backtrace

$ RUST_BACKTRACE=1 cargo build

   Compiling bug v0.1.0 (/home/mareksom/lab/bug)
warning: struct is never constructed: `A`
 --> src/main.rs:1:8
  |
1 | struct A<const M: u32> {}
  |        ^
  |
  = note: `#[warn(dead_code)]` on by default

warning: struct is never constructed: `B`
 --> src/main.rs:3:8
  |
3 | struct B<const M: u32> {}
  |        ^

warning: associated constant is never used: `M`
 --> src/main.rs:6:3
  |
6 |   const M: u32 = M;
  |   ^^^^^^^^^^^^^^^^^

warning: struct is never constructed: `C`
 --> src/main.rs:9:8
  |
9 | struct C<const M: u32> {
  |        ^

warning: Error finalizing incremental compilation session directory `/home/mareksom/lab/bug/target/debug/incremental/bug-3u769ve6liwcr/s-g9f1uxo5u4-1eiyj2b-working`: No such file or directory (os error 2)

error: internal compiler error: min_const_generics resolve check didn't stop compilation
  --> src/main.rs:10:9
   |
10 |   a: A<{B::<1>::M}>,
   |         ^^^^^^^^^
   |
   = note: delayed at compiler/rustc_resolve/src/lib.rs:2886:46

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', compiler/rustc_errors/src/lib.rs:1176:13
stack backtrace:
   0: rust_begin_unwind
             at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/panicking.rs:584:5
   1: core::panicking::panic_fmt
             at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/core/src/panicking.rs:143:14
   2: core::panicking::panic_display::<&str>
   3: <rustc_errors::HandlerInner>::flush_delayed
   4: <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop
   5: core::ptr::drop_in_place::<rustc_session::parse::ParseSess>
   6: <alloc::rc::Rc<rustc_session::session::Session> as core::ops::drop::Drop>::drop
   7: core::ptr::drop_in_place::<rustc_interface::interface::Compiler>
   8: rustc_interface::interface::create_compiler_and_run::<core::result::Result<(), rustc_errors::ErrorReported>, rustc_driver::run_compiler::{closure#1}>
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 1.60.0 (7737e0b5c 2022-04-04) running on x86_64-unknown-linux-gnu

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

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

query stack during panic:
end of query stack
warning: `bug` (bin "bug") generated 5 warnings
error: could not compile `bug`; 5 warnings emitted

[lqd]

Interestingly enough:

• this doesn't seem related to incremental compilation (it reproduces with CARGO_INCREMENTAL=0)
• doesn't occur on nightly
• and seems to have been fixed by resolve: Do not build expensive suggestions if they are not actually used #95255

It's a bit unclear to me why that PR fixed it (and that ICE looks at least a year old), but in any case this piece of code will stop ICEing in 1.61, releasing in a couple weeks.