ice: mir_const_qualif: MIR had errors

[matthiaskrgr]

auto-reduced (treereduce-rust):

//!

//!

//!

//! }
//! ```

use std::mem;

macro_rules! define_reify_functions {
    ($(
        fn $name:ident $(<$($param:ident),*>)?
            for $(extern $abi:tt)? fn($($arg:ident: $arg_ty:ty),*) -> $ret_ty:ty;
    )+) => {
        $(pub const fn $name<
            $($($param,)*)?
            F: Fn($($arg_ty),*) -> $ret_ty + Copy
        >(f: F) -> $(extern $abi)? fn($($arg_ty),*) -> $ret_ty {


            assert!(mem::size_of::<F>() == 0, );

            $(extern $abi)? fn wrapper<
                $($($param,)*)?
                F: Fn($($arg_ty),*) -> $ret_ty + Copy
            >($($arg: $arg_ty),*) -> $ret_ty {
                let f = unsafe {


                    mem::MaybeUninit::<F>::uninit().assume_init()
                };
                f($($arg),*)
            }
            let _f_proof = f;
            wrapper::<
                $($($param,)*)?
                F
            >
        })+
    }
}

define_reify_functions! {
    fn _reify_to_extern_c_fn_unary<A, R> for extern "C" fn(arg: A) -> R;






    fn reify_to_extern_c_fn_hrt_bridge<R> for extern "C" fn(bridge: super::BridgeConfig<'_>) -> R;
}

original code

original:

//! Abstraction for creating `fn` pointers from any callable that *effectively*
//! has the equivalent of implementing `Default`, even if the compiler neither
//! provides `Default` nor allows reifying closures (i.e. creating `fn` pointers)
//! other than those with absolutely no captures.
//!
//! More specifically, for a closure-like type to be "effectively `Default`":
//! * it must be a ZST (zero-sized type): no information contained within, so
//!   that `Default`'s return value (if it were implemented) is unambiguous
//! * it must be `Copy`: no captured "unique ZST tokens" or any other similar
//!   types that would make duplicating values at will unsound
//!   * combined with the ZST requirement, this confers a kind of "telecopy"
//!     ability: similar to `Copy`, but without keeping the value around, and
//!     instead "reconstructing" it (a noop given it's a ZST) when needed
//! * it must be *provably* inhabited: no captured uninhabited types or any
//!   other types that cannot be constructed by the user of this abstraction
//!   * the proof is a value of the closure-like type itself, in a sense the
//!     "seed" for the "telecopy" process made possible by ZST + `Copy`
//!   * this requirement is the only reason an abstraction limited to a specific
//!     usecase is required: ZST + `Copy` can be checked with *at worst* a panic
//!     at the "attempted `::default()` call" time, but that doesn't guarantee
//!     that the value can be soundly created, and attempting to use the typical
//!     "proof ZST token" approach leads yet again to having a ZST + `Copy` type
//!     that is not proof of anything without a value (i.e. isomorphic to a
//!     newtype of the type it's trying to prove the inhabitation of)
//!
//! A more flexible (and safer) solution to the general problem could exist once
//! `const`-generic parameters can have type parameters in their types:
//!
//! ```rust,ignore (needs future const-generics)
//! extern "C" fn ffi_wrapper<
//!     A, R,
//!     F: Fn(A) -> R,
//!     const f: F, // <-- this `const`-generic is not yet allowed
//! >(arg: A) -> R {
//!     f(arg)
//! }
//! ```

use std::mem;

// FIXME(eddyb) this could be `trait` impls except for the `const fn` requirement.
macro_rules! define_reify_functions {
    ($(
        fn $name:ident $(<$($param:ident),*>)?
            for $(extern $abi:tt)? fn($($arg:ident: $arg_ty:ty),*) -> $ret_ty:ty;
    )+) => {
        $(pub const fn $name<
            $($($param,)*)?
            F: Fn($($arg_ty),*) -> $ret_ty + Copy
        >(f: F) -> $(extern $abi)? fn($($arg_ty),*) -> $ret_ty {
            // FIXME(eddyb) describe the `F` type (e.g. via `type_name::<F>`) once panic
            // formatting becomes possible in `const fn`.
            assert!(mem::size_of::<F>() == 0, "selfless_reify: closure must be zero-sized");

            $(extern $abi)? fn wrapper<
                $($($param,)*)?
                F: Fn($($arg_ty),*) -> $ret_ty + Copy
            >($($arg: $arg_ty),*) -> $ret_ty {
                let f = unsafe {
                    // SAFETY: `F` satisfies all criteria for "out of thin air"
                    // reconstructability (see module-level doc comment).
                    mem::MaybeUninit::<F>::uninit().assume_init()
                };
                f($($arg),*)
            }
            let _f_proof = f;
            wrapper::<
                $($($param,)*)?
                F
            >
        })+
    }
}

define_reify_functions! {
    fn _reify_to_extern_c_fn_unary<A, R> for extern "C" fn(arg: A) -> R;

    // HACK(eddyb) this abstraction is used with `for<'a> fn(BridgeConfig<'a>)
    // -> T` but that doesn't work with just `reify_to_extern_c_fn_unary`
    // because of the `fn` pointer type being "higher-ranked" (i.e. the
    // `for<'a>` binder).
    // FIXME(eddyb) try to remove the lifetime from `BridgeConfig`, that'd help.
    fn reify_to_extern_c_fn_hrt_bridge<R> for extern "C" fn(bridge: super::BridgeConfig<'_>) -> R;
}

Version information

rustc 1.78.0-nightly (340bb19fe 2024-02-14)
binary: rustc
commit-hash: 340bb19fea20fd5f9357bbfac542fad84fc7ea2b
commit-date: 2024-02-14
host: x86_64-unknown-linux-gnu
release: 1.78.0-nightly
LLVM version: 18.1.0

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc --crate-type=lib

Program output

thread 'rustc' panicked at compiler/rustc_mir_transform/src/lib.rs:268:9:
mir_const_qualif: MIR had errors
stack backtrace:
   0:     0x7f406118ce46 - std::backtrace_rs::backtrace::libunwind::trace::h741b35e6ebf0ea82
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5
   1:     0x7f406118ce46 - std::backtrace_rs::backtrace::trace_unsynchronized::hf3b09a36cbdb818e
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f406118ce46 - std::sys_common::backtrace::_print_fmt::hd9ddcb56e855ae1f
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f406118ce46 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h1d659f3f1b376713
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f40611dd46c - core::fmt::rt::Argument::fmt::h268aa39b6fb00372
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/core/src/fmt/rt.rs:142:9
   5:     0x7f40611dd46c - core::fmt::write::h3ca4c8a121ee4a21
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/core/src/fmt/mod.rs:1120:17
   6:     0x7f406118087f - std::io::Write::write_fmt::hbae5643614f30ef5
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/io/mod.rs:1854:15
   7:     0x7f406118cbf4 - std::sys_common::backtrace::_print::h46251963e880a6db
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f406118cbf4 - std::sys_common::backtrace::print::hf7d8eafd5758e700
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f406118f93b - std::panicking::default_hook::{{closure}}::h762f7d01310422ff
  10:     0x7f406118f689 - std::panicking::default_hook::h6bf045830ee7f539
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/panicking.rs:292:9
  11:     0x7f4063ff2bac - std[3c399c9137e7035e]::panicking::update_hook::<alloc[b5118abce3d9b84a]::boxed::Box<rustc_driver_impl[aed52aad4ff697f9]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7f40611900a0 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h183d4d6c4a9f8452
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/alloc/src/boxed.rs:2030:9
  13:     0x7f40611900a0 - std::panicking::rust_panic_with_hook::hf47919d70d1ff480
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/panicking.rs:785:13
  14:     0x7f406118fda9 - std::panicking::begin_panic_handler::{{closure}}::h5fbc7433175e9186
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/panicking.rs:651:13
  15:     0x7f406118d326 - std::sys_common::backtrace::__rust_end_short_backtrace::h2b0c01029bb6a245
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/sys_common/backtrace.rs:171:18
  16:     0x7f406118fb14 - rust_begin_unwind
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/panicking.rs:647:5
  17:     0x7f40611d9975 - core::panicking::panic_fmt::h213e6f8381440dd9
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/core/src/panicking.rs:72:14
  18:     0x7f4065528ff1 - rustc_mir_transform[a16df670bd198a8c]::mir_const_qualif
  19:     0x7f4065528d21 - rustc_query_impl[2b06c656d5e1ef18]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[2b06c656d5e1ef18]::query_impl::mir_const_qualif::dynamic_query::{closure#2}::{closure#0}, rustc_middle[70484f9a8b697519]::query::erase::Erased<[u8; 4usize]>>
  20:     0x7f406552804b - rustc_query_system[27a374b315d29eb0]::query::plumbing::try_execute_query::<rustc_query_impl[2b06c656d5e1ef18]::DynamicConfig<rustc_query_system[27a374b315d29eb0]::query::caches::DefIdCache<rustc_middle[70484f9a8b697519]::query::erase::Erased<[u8; 4usize]>>, false, false, false>, rustc_query_impl[2b06c656d5e1ef18]::plumbing::QueryCtxt, false>
  21:     0x7f4065527dc9 - rustc_query_impl[2b06c656d5e1ef18]::query_impl::mir_const_qualif::get_query_non_incr::__rust_end_short_backtrace
  22:     0x7f4065527bfe - rustc_middle[70484f9a8b697519]::query::plumbing::query_get_at::<rustc_query_system[27a374b315d29eb0]::query::caches::DefIdCache<rustc_middle[70484f9a8b697519]::query::erase::Erased<[u8; 4usize]>>>
  23:     0x7f406358f097 - rustc_mir_transform[a16df670bd198a8c]::mir_promoted
  24:     0x7f40657fb812 - rustc_query_impl[2b06c656d5e1ef18]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[2b06c656d5e1ef18]::query_impl::mir_promoted::dynamic_query::{closure#2}::{closure#0}, rustc_middle[70484f9a8b697519]::query::erase::Erased<[u8; 16usize]>>
  25:     0x7f40657fbabb - rustc_query_system[27a374b315d29eb0]::query::plumbing::try_execute_query::<rustc_query_impl[2b06c656d5e1ef18]::DynamicConfig<rustc_query_system[27a374b315d29eb0]::query::caches::VecCache<rustc_span[193b94924c128396]::def_id::LocalDefId, rustc_middle[70484f9a8b697519]::query::erase::Erased<[u8; 16usize]>>, false, false, false>, rustc_query_impl[2b06c656d5e1ef18]::plumbing::QueryCtxt, false>
  26:     0x7f40660a745d - rustc_query_impl[2b06c656d5e1ef18]::query_impl::mir_promoted::get_query_non_incr::__rust_end_short_backtrace
  27:     0x7f40660a756e - rustc_borrowck[90372d0f1f178afe]::mir_borrowck
  28:     0x7f40660a74a1 - rustc_query_impl[2b06c656d5e1ef18]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[2b06c656d5e1ef18]::query_impl::mir_borrowck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[70484f9a8b697519]::query::erase::Erased<[u8; 8usize]>>
  29:     0x7f40653858f0 - rustc_query_system[27a374b315d29eb0]::query::plumbing::try_execute_query::<rustc_query_impl[2b06c656d5e1ef18]::DynamicConfig<rustc_query_system[27a374b315d29eb0]::query::caches::VecCache<rustc_span[193b94924c128396]::def_id::LocalDefId, rustc_middle[70484f9a8b697519]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[2b06c656d5e1ef18]::plumbing::QueryCtxt, false>
  30:     0x7f406538540c - rustc_query_impl[2b06c656d5e1ef18]::query_impl::mir_borrowck::get_query_non_incr::__rust_end_short_backtrace
  31:     0x7f4065c136f0 - rustc_interface[85a46e65fd36dd64]::passes::analysis
  32:     0x7f4065c131e9 - rustc_query_impl[2b06c656d5e1ef18]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[2b06c656d5e1ef18]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[70484f9a8b697519]::query::erase::Erased<[u8; 1usize]>>
  33:     0x7f40661b0025 - rustc_query_system[27a374b315d29eb0]::query::plumbing::try_execute_query::<rustc_query_impl[2b06c656d5e1ef18]::DynamicConfig<rustc_query_system[27a374b315d29eb0]::query::caches::SingleCache<rustc_middle[70484f9a8b697519]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[2b06c656d5e1ef18]::plumbing::QueryCtxt, false>
  34:     0x7f40661afd89 - rustc_query_impl[2b06c656d5e1ef18]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  35:     0x7f406602e055 - rustc_interface[85a46e65fd36dd64]::interface::run_compiler::<core[7e3aa1eb1ad3b865]::result::Result<(), rustc_span[193b94924c128396]::ErrorGuaranteed>, rustc_driver_impl[aed52aad4ff697f9]::run_compiler::{closure#0}>::{closure#0}
  36:     0x7f40661c7b58 - std[3c399c9137e7035e]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[85a46e65fd36dd64]::util::run_in_thread_with_globals<rustc_interface[85a46e65fd36dd64]::util::run_in_thread_pool_with_globals<rustc_interface[85a46e65fd36dd64]::interface::run_compiler<core[7e3aa1eb1ad3b865]::result::Result<(), rustc_span[193b94924c128396]::ErrorGuaranteed>, rustc_driver_impl[aed52aad4ff697f9]::run_compiler::{closure#0}>::{closure#0}, core[7e3aa1eb1ad3b865]::result::Result<(), rustc_span[193b94924c128396]::ErrorGuaranteed>>::{closure#0}, core[7e3aa1eb1ad3b865]::result::Result<(), rustc_span[193b94924c128396]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[7e3aa1eb1ad3b865]::result::Result<(), rustc_span[193b94924c128396]::ErrorGuaranteed>>
  37:     0x7f40661c7984 - <<std[3c399c9137e7035e]::thread::Builder>::spawn_unchecked_<rustc_interface[85a46e65fd36dd64]::util::run_in_thread_with_globals<rustc_interface[85a46e65fd36dd64]::util::run_in_thread_pool_with_globals<rustc_interface[85a46e65fd36dd64]::interface::run_compiler<core[7e3aa1eb1ad3b865]::result::Result<(), rustc_span[193b94924c128396]::ErrorGuaranteed>, rustc_driver_impl[aed52aad4ff697f9]::run_compiler::{closure#0}>::{closure#0}, core[7e3aa1eb1ad3b865]::result::Result<(), rustc_span[193b94924c128396]::ErrorGuaranteed>>::{closure#0}, core[7e3aa1eb1ad3b865]::result::Result<(), rustc_span[193b94924c128396]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[7e3aa1eb1ad3b865]::result::Result<(), rustc_span[193b94924c128396]::ErrorGuaranteed>>::{closure#1} as core[7e3aa1eb1ad3b865]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  38:     0x7f40611991e5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h1516af221a452bc1
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/alloc/src/boxed.rs:2016:9
  39:     0x7f40611991e5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hff2a9d52ad89d581
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/alloc/src/boxed.rs:2016:9
  40:     0x7f40611991e5 - std::sys::pal::unix::thread::Thread::new::thread_start::hf359248e8c5b2b25
                               at /rustc/340bb19fea20fd5f9357bbfac542fad84fc7ea2b/library/std/src/sys/pal/unix/thread.rs:108:17
  41:     0x7f4060f4a9eb - <unknown>
  42:     0x7f4060fce7cc - <unknown>
  43:                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-nightly (340bb19fe 2024-02-14) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -Z dump-mir-dir=dir

query stack during panic:
#0 [mir_const_qualif] const checking `reify_to_extern_c_fn_hrt_bridge`
#1 [mir_promoted] promoting constants in MIR for `reify_to_extern_c_fn_hrt_bridge`
#2 [mir_borrowck] borrow-checking `reify_to_extern_c_fn_hrt_bridge`
#3 [analysis] running analysis passes on this crate
end of query stack
error[E0433]: failed to resolve: there are too many leading `super` keywords
  --> /tmp/icemaker_global_tempdir.PRGFGEJ4g674/rustc_testrunner_tmpdir_reporting.rq3zBfWzREvH/mvce.rs:53:69
   |
53 |     fn reify_to_extern_c_fn_hrt_bridge<R> for extern "C" fn(bridge: super::BridgeConfig<'_>) -> R;
   |                                                                     ^^^^^ there are too many leading `super` keywords

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0433`.

[matthiaskrgr]

Test is from library/proc_macro/src/bridge/selfless_reify.rs originally

cleaned up a bit

use std::mem;

macro_rules! define_reify_functions {
    ($(
        fn $name:ident $(<$($param:ident),*>)?
            for $(extern $abi:tt)? fn($($arg:ident: $arg_ty:ty),*) -> $ret_ty:ty;
    )+) => {
        $(pub const fn $name<
            $($($param,)*)?
            F: Fn($($arg_ty),*) -> $ret_ty + Copy
        >(f: F) -> $(extern $abi)? fn($($arg_ty),*) -> $ret_ty {


            assert!(mem::size_of::<F>() == 0, );

            $(extern $abi)? fn wrapper<
                $($($param,)*)?
                F: Fn($($arg_ty),*) -> $ret_ty + Copy
            >($($arg: $arg_ty),*) -> $ret_ty {
                let f = unsafe {


                    mem::MaybeUninit::<F>::uninit().assume_init()
                };
                f($($arg),*)
            }
            let _f_proof = f;
            wrapper::<
                $($($param,)*)?
                F
            >
        })+
    }
}

define_reify_functions! {
    fn _reify_to_extern_c_fn_unary<A, R> for extern "C" fn(arg: A) -> R;

    fn reify_to_extern_c_fn_hrt_bridge<R> for extern "C" fn(bridge: super::BridgeConfig<'_>) -> R;
}

[matthiaskrgr]

Regression in #121071 cc @nnethercote

[matthiaskrgr]

Another smaller example :3

fn main(_: <lib2::GenericType<42> as lib2::TypeFn>::Output) {}

[jieyouxu]

@rustbot label +A-mir -needs-triage