underflow while calculating type sizes

[matthiaskrgr]

only happens when rustc is compiled with debug assertions enabled

auto-reduced (treereduce-rust):

#[repr(align(4))]
enum AlsoAlign16 {
    Foo { limb_with_noniche16: NoNiche16 },
    Bar,
}

struct NoNiche16(u64, u64);

fn main() {}

original code

original:

//@ run-pass
#![allow(dead_code)]

use std::mem;

// Raising alignment
#[repr(align(16))]
enum Align16 {
    Foo { foo: u32 },
    Bar { bar: u32 },
}

// Raise alignment by maximum
#[repr(align(1), align(16))]
#[repr(align(32))]
#[repr(align(4))]
enum Align32 {
    Foo,
    Bar,
}

// Not reducing alignment
#[repr(align(4))]
enum AlsoAlign16 {
    Foo { limb_with_noniche16: NoNiche16 },
    Bar,
}

// No niche for discriminant when used as limb
#[repr(align(16))]
struct NoNiche16(u64, u64);

// Discriminant will require extra space, but enum needs to stay compatible
// with alignment 16
#[repr(align(1))]
enum AnotherAlign16 {
    Foo { limb_with_noniche16: NoNiche16 },
    Bar,
    Baz,
}

fn main() {
    assert_eq!(mem::align_of::<Align16>(), 16);
    assert_eq!(mem::size_of::<Align16>(), 16);

    assert_eq!(mem::align_of::<Align32>(), 1);
    assert_eq!(mem::size_of::<Align32>(), 32);

    assert_eq!(mem::align_of::<AlsoAlign16>(), 16);
    assert_eq!(mem::size_of::<AlsoAlign16>(), 16);

    assert_eq!(mem::align_of::<AnotherAlign16>(), 16);
    assert_eq!(mem::size_of::<AnotherAlign16>(), 32);
}

Version information

rustc 1.78.0-dev
binary: rustc
commit-hash: unknown
commit-date: unknown
host: x86_64-unknown-linux-gnu
release: 1.78.0-dev
LLVM version: 18.1.0

Command:
/home/matthias/.rustup/toolchains/local-debug-assertions/bin/rustc -Zprint-type-sizes

Program output

warning: enum `AlsoAlign16` is never used
 --> /tmp/icemaker_global_tempdir.jQa79k0ZO1IC/rustc_testrunner_tmpdir_reporting.vxVUC0DEKwwH/mvce.rs:2:6
  |
2 | enum AlsoAlign16 {
  |      ^^^^^^^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

warning: struct `NoNiche16` is never constructed
 --> /tmp/icemaker_global_tempdir.jQa79k0ZO1IC/rustc_testrunner_tmpdir_reporting.vxVUC0DEKwwH/mvce.rs:7:8
  |
7 | struct NoNiche16(u64, u64);
  |        ^^^^^^^^^

thread 'rustc' panicked at compiler/rustc_session/src/code_stats.rs:176:32:
attempt to subtract with overflow
stack backtrace:
   0:     0x7f6901ded829 - std::backtrace_rs::backtrace::libunwind::trace::h71aa28bdc5089aab
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/../../backtrace/src/backtrace/libunwind.rs:105:5
   1:     0x7f6901ded829 - std::backtrace_rs::backtrace::trace_unsynchronized::hc71f6f29c4d7cf67
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f6901ded829 - std::sys_common::backtrace::_print_fmt::h8e1e2ea27397ed17
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f6901ded829 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h28aca7b36a9d50a9
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f6901e82737 - core::fmt::rt::Argument::fmt::h67bfbe6caf20ecda
                               at /home/matthias/vcs/github/rust_debug_assertions/library/core/src/fmt/rt.rs:142:9
   5:     0x7f6901e82737 - core::fmt::write::h2b3e0bd86bdfc209
                               at /home/matthias/vcs/github/rust_debug_assertions/library/core/src/fmt/mod.rs:1153:17
   6:     0x7f6901e01855 - std::io::Write::write_fmt::h136db78b548c4ef6
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/io/mod.rs:1843:15
   7:     0x7f6901ded5e4 - std::sys_common::backtrace::_print::h5b92b1853c8de3bd
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f6901ded5e4 - std::sys_common::backtrace::print::h490b617a207e3b67
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f6901e11733 - std::panicking::default_hook::{{closure}}::h45adea5532c8b211
  10:     0x7f6901e11431 - std::panicking::default_hook::hd02efd9905101244
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/panicking.rs:292:9
  11:     0x7f68fe91e6f8 - rustc_driver_impl[392676b3d88fadab]::install_ice_hook::{closure#0}
                               at /home/matthias/vcs/github/rust_debug_assertions/compiler/rustc_driver_impl/src/lib.rs:1350:17
  12:     0x7f68fe91e6f8 - <alloc[7d65993373035c28]::boxed::Box<rustc_driver_impl[392676b3d88fadab]::install_ice_hook::{closure#0}> as core[aa444211b5f41879]::ops::function::Fn<(&dyn for<'a, 'b> core[aa444211b5f41879]::ops::function::Fn<(&'a core[aa444211b5f41879]::panic::panic_info::PanicInfo<'b>,), Output = ()> + core[aa444211b5f41879]::marker::Sync + core[aa444211b5f41879]::marker::Send, &core[aa444211b5f41879]::panic::panic_info::PanicInfo)>>::call
                               at /home/matthias/vcs/github/rust_debug_assertions/library/alloc/src/boxed.rs:2034:9
  13:     0x7f6901e11e65 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::hc3e26a573d0d775a
                               at /home/matthias/vcs/github/rust_debug_assertions/library/alloc/src/boxed.rs:2034:9
  14:     0x7f6901e11e65 - std::panicking::rust_panic_with_hook::h62b1349491684a47
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/panicking.rs:783:13
  15:     0x7f6901dee699 - std::panicking::begin_panic_handler::{{closure}}::ha9ba801d79b7df26
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/panicking.rs:649:13
  16:     0x7f6901dedad6 - std::sys_common::backtrace::__rust_end_short_backtrace::h143ebb6cbd4c764e
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/sys_common/backtrace.rs:171:18
  17:     0x7f6901e11a34 - rust_begin_unwind
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/panicking.rs:645:5
  18:     0x7f6901e9b425 - core::panicking::panic_fmt::h7cdaca6ac7987f65
                               at /home/matthias/vcs/github/rust_debug_assertions/library/core/src/panicking.rs:72:14
  19:     0x7f6901e9b4d5 - core::panicking::panic::h0a00db0f39d75437
                               at /home/matthias/vcs/github/rust_debug_assertions/library/core/src/panicking.rs:145:5
  20:     0x7f6900e5db52 - <rustc_session[96c1b509bcbd92de]::code_stats::CodeStats>::print_type_sizes
                               at /home/matthias/vcs/github/rust_debug_assertions/compiler/rustc_session/src/code_stats.rs:176:32
  21:     0x7f68fe944339 - rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}::{closure#1}
                               at /home/matthias/vcs/github/rust_debug_assertions/compiler/rustc_driver_impl/src/lib.rs:451:17
  22:     0x7f68fe944339 - <rustc_interface[e9562a9c472c94f0]::interface::Compiler>::enter::<rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}::{closure#1}, core[aa444211b5f41879]::result::Result<core[aa444211b5f41879]::option::Option<rustc_interface[e9562a9c472c94f0]::queries::Linker>, rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>
                               at /home/matthias/vcs/github/rust_debug_assertions/compiler/rustc_interface/src/queries.rs:309:19
  23:     0x7f68fe974320 - rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}
                               at /home/matthias/vcs/github/rust_debug_assertions/compiler/rustc_driver_impl/src/lib.rs:388:22
  24:     0x7f68fe974320 - rustc_interface[e9562a9c472c94f0]::interface::run_compiler::<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}::{closure#0}
                               at /home/matthias/vcs/github/rust_debug_assertions/compiler/rustc_interface/src/interface.rs:477:31
  25:     0x7f68fe974320 - rustc_span[87e9bd33af79061d]::set_source_map::<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}::{closure#0}>
                               at /home/matthias/vcs/github/rust_debug_assertions/compiler/rustc_span/src/lib.rs:1275:5
  26:     0x7f68fe9251b2 - rustc_interface[e9562a9c472c94f0]::interface::run_compiler::<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}
                               at /home/matthias/vcs/github/rust_debug_assertions/compiler/rustc_interface/src/interface.rs:463:13
  27:     0x7f68fe9251b2 - rustc_interface[e9562a9c472c94f0]::util::run_in_thread_pool_with_globals::<rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}
                               at /home/matthias/vcs/github/rust_debug_assertions/compiler/rustc_interface/src/util.rs:119:13
  28:     0x7f68fe9251b2 - <scoped_tls[af7c8664e9f149d3]::ScopedKey<rustc_span[87e9bd33af79061d]::SessionGlobals>>::set::<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_pool_with_globals<rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>
                               at /home/matthias/.cargo/registry/src/index.crates.io-6f17d22bba15001f/scoped-tls-1.0.1/src/lib.rs:137:9
  29:     0x7f68fe97e341 - rustc_span[87e9bd33af79061d]::create_session_globals_then::<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_interface[e9562a9c472c94f0]::util::run_in_thread_pool_with_globals<rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}>
                               at /home/matthias/vcs/github/rust_debug_assertions/compiler/rustc_span/src/lib.rs:136:5
  30:     0x7f68fe97e341 - rustc_interface[e9562a9c472c94f0]::util::run_in_thread_with_globals::<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_pool_with_globals<rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}::{closure#0}
                               at /home/matthias/vcs/github/rust_debug_assertions/compiler/rustc_interface/src/util.rs:80:38
  31:     0x7f68fe97e341 - std[9e45a94ab2b939d9]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_with_globals<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_pool_with_globals<rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/sys_common/backtrace.rs:155:18
  32:     0x7f68fe931da3 - <std[9e45a94ab2b939d9]::thread::Builder>::spawn_unchecked_::<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_with_globals<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_pool_with_globals<rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#1}::{closure#0}
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/thread/mod.rs:528:17
  33:     0x7f68fe931da3 - <core[aa444211b5f41879]::panic::unwind_safe::AssertUnwindSafe<<std[9e45a94ab2b939d9]::thread::Builder>::spawn_unchecked_<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_with_globals<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_pool_with_globals<rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#1}::{closure#0}> as core[aa444211b5f41879]::ops::function::FnOnce<()>>::call_once
                               at /home/matthias/vcs/github/rust_debug_assertions/library/core/src/panic/unwind_safe.rs:272:9
  34:     0x7f68fe931da3 - std[9e45a94ab2b939d9]::panicking::try::do_call::<core[aa444211b5f41879]::panic::unwind_safe::AssertUnwindSafe<<std[9e45a94ab2b939d9]::thread::Builder>::spawn_unchecked_<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_with_globals<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_pool_with_globals<rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#1}::{closure#0}>, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/panicking.rs:552:40
  35:     0x7f68fe931da3 - std[9e45a94ab2b939d9]::panicking::try::<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, core[aa444211b5f41879]::panic::unwind_safe::AssertUnwindSafe<<std[9e45a94ab2b939d9]::thread::Builder>::spawn_unchecked_<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_with_globals<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_pool_with_globals<rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#1}::{closure#0}>>
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/panicking.rs:516:19
  36:     0x7f68fe931da3 - std[9e45a94ab2b939d9]::panic::catch_unwind::<core[aa444211b5f41879]::panic::unwind_safe::AssertUnwindSafe<<std[9e45a94ab2b939d9]::thread::Builder>::spawn_unchecked_<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_with_globals<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_pool_with_globals<rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#1}::{closure#0}>, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/panic.rs:146:14
  37:     0x7f68fe931da3 - <std[9e45a94ab2b939d9]::thread::Builder>::spawn_unchecked_::<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_with_globals<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_pool_with_globals<rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#1}
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/thread/mod.rs:527:30
  38:     0x7f68fe931da3 - <<std[9e45a94ab2b939d9]::thread::Builder>::spawn_unchecked_<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_with_globals<rustc_interface[e9562a9c472c94f0]::util::run_in_thread_pool_with_globals<rustc_interface[e9562a9c472c94f0]::interface::run_compiler<core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>, rustc_driver_impl[392676b3d88fadab]::run_compiler::{closure#0}>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[aa444211b5f41879]::result::Result<(), rustc_span[87e9bd33af79061d]::ErrorGuaranteed>>::{closure#1} as core[aa444211b5f41879]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
                               at /home/matthias/vcs/github/rust_debug_assertions/library/core/src/ops/function.rs:250:5
  39:     0x7f6901de823e - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h6534edd00de45d0a
                               at /home/matthias/vcs/github/rust_debug_assertions/library/alloc/src/boxed.rs:2020:9
  40:     0x7f6901de823e - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hfc923cc959abd00c
                               at /home/matthias/vcs/github/rust_debug_assertions/library/alloc/src/boxed.rs:2020:9
  41:     0x7f6901de823e - std::sys::pal::unix::thread::Thread::new::thread_start::h57135b15377165e8
                               at /home/matthias/vcs/github/rust_debug_assertions/library/std/src/sys/pal/unix/thread.rs:108:17
  42:     0x7f68fbca955a - <unknown>
  43:     0x7f68fbd26a3c - <unknown>
  44:                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: rustc 1.78.0-dev running on x86_64-unknown-linux-gnu

note: compiler flags: -Z print-type-sizes -Z dump-mir-dir=dir

query stack during panic:
end of query stack
warning: 2 warnings emitted

[matthiaskrgr]

print-type-size type: `unwind::libunwind::_Unwind_Exception`: 32 bytes, alignment: 8 bytes
print-type-size     field `.exception_class`: 8 bytes
print-type-size     field `.exception_cleanup`: 8 bytes
print-type-size     field `.private`: 16 bytes
print-type-size type: `AlsoAlign16`: 24 bytes, alignment: 8 bytes
print-type-size     discriminant: 8 bytes
print-type-size     variant `Foo`: 16 bytes
print-type-size         field `.limb_with_noniche16`: 16 bytes
print-type-size     variant `Bar`: 18446744073709551612 bytes  // <<<<<<<<<<<<<< ------------- lol

[matthiaskrgr]

without debug assertions:

print-type-size type: `unwind::libunwind::_Unwind_Exception`: 32 bytes, alignment: 8 bytes
print-type-size     field `.exception_class`: 8 bytes
print-type-size     field `.exception_cleanup`: 8 bytes
print-type-size     field `.private`: 16 bytes
print-type-size type: `AlsoAlign16`: 24 bytes, alignment: 8 bytes
print-type-size     discriminant: 8 bytes
print-type-size     variant `Foo`: 16 bytes
print-type-size         field `.limb_with_noniche16`: 16 bytes
print-type-size     variant `Bar`: 18446744073709551612 bytes
print-type-size type: `NoNiche16`: 16 bytes, alignment: 8 bytes
print-type-size     field `.0`: 8 bytes
print-type-size     field `.1`: 8 bytes
print-type-size type: `std::option::Option<extern "C" fn(unwind::libunwind::_Unwind_Reason_Code, *mut unwind::libunwind::_Unwind_Exception)>`: 8 bytes, alignment: 8 bytes
print-type-size     variant `Some`: 8 bytes
print-type-size         field `.0`: 8 bytes
print-type-size     variant `None`: 0 bytes
print-type-size type: `std::ptr::DynMetadata<dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>`: 8 bytes, alignment: 8 bytes
print-type-size     field `.vtable_ptr`: 8 bytes
print-type-size     field `.phantom`: 0 bytes
print-type-size type: `std::result::Result<isize, !>`: 8 bytes, alignment: 8 bytes
print-type-size     variant `Ok`: 8 bytes
print-type-size         field `.0`: 8 bytes
print-type-size type: `{closure@std::rt::lang_start<()>::{closure#0}}`: 8 bytes, alignment: 8 bytes
print-type-size     end padding: 8 bytes
print-type-size type: `unwind::libunwind::_Unwind_Action`: 4 bytes, alignment: 4 bytes
print-type-size     discriminant: 4 bytes
print-type-size     variant `_UA_SEARCH_PHASE`: 0 bytes
print-type-size     variant `_UA_CLEANUP_PHASE`: 0 bytes
print-type-size     variant `_UA_HANDLER_FRAME`: 0 bytes
print-type-size     variant `_UA_FORCE_UNWIND`: 0 bytes
print-type-size     variant `_UA_END_OF_STACK`: 0 bytes
print-type-size type: `unwind::libunwind::_Unwind_Reason_Code`: 4 bytes, alignment: 4 bytes
print-type-size     discriminant: 4 bytes
print-type-size     variant `_URC_NO_REASON`: 0 bytes
print-type-size     variant `_URC_FOREIGN_EXCEPTION_CAUGHT`: 0 bytes
print-type-size     variant `_URC_FATAL_PHASE2_ERROR`: 0 bytes
print-type-size     variant `_URC_FATAL_PHASE1_ERROR`: 0 bytes
print-type-size     variant `_URC_NORMAL_STOP`: 0 bytes
print-type-size     variant `_URC_END_OF_STACK`: 0 bytes
print-type-size     variant `_URC_HANDLER_FOUND`: 0 bytes
print-type-size     variant `_URC_INSTALL_CONTEXT`: 0 bytes
print-type-size     variant `_URC_CONTINUE_UNWIND`: 0 bytes
print-type-size     variant `_URC_FAILURE`: 0 bytes
print-type-size type: `std::process::ExitCode`: 1 bytes, alignment: 1 bytes
print-type-size     field `.0`: 1 bytes
print-type-size type: `std::sys::pal::unix::process::process_common::ExitCode`: 1 bytes, alignment: 1 bytes
print-type-size     field `.0`: 1 bytes
print-type-size type: `std::marker::PhantomData<dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>`: 0 bytes, alignment: 1 bytes
print-type-size type: `unwind::libunwind::_Unwind_Context`: 0 bytes, alignment: 1 bytes

[compiler-errors]

A "quick" fix would probably need to do saturating sub...

[lolbinarycat]

triage: no ice on stable or nightly rust (playground)

[matthiaskrgr]

this requires debug assertions...