ICE: `expected type for .. but found Const(false) when instantiating`

[matthiaskrgr]

auto-reduced (treereduce-rust):

#![feature(const_trait_impl, effects)]

trait Add42 {}

impl const Add42 for () {
    fn add<A: ~const Add42>(self) -> Foo {
        Foo
    }
}

original:

#![feature(const_trait_impl, effects)]
#![feature(generic_arg_infer)]
#![feature(generic_const_exprs)]
#![allow(incomplete_features)]

struct Foo<const N: usize>;

impl<const N: usize> Foo<N> {
    fn add<A: ~const Add42>(self) -> Foo<{ A::add(N) }> {
        //~^ ERROR `~const` is not allowed here
        //~| ERROR mismatched types
        Foo
    }
}

#[const_trait]
trait Add42 {
    fn add(a: usize) -> usize;
}

impl const Add42 for () {
    fn add<A: ~const Add42>(self) -> Foo<{ A::add(N) }> {
        //~^ ERROR `~const` is not allowed here
        //~| ERROR mismatched types
        Foo
    }
}

fn bar<A: const Add42, const N: usize>(_: Foo<N>) -> Foo<{ A::add(N) }> {
    //~^ ERROR `~const` is not allowed here
    //~| ERROR mismatched types
    Foo
}

fn main() {
    let foo = Foo::<0>;
    let foo = bar::<(), _>(foo);
    let _foo = bar::<(), _>(foo);
}

Version information

rustc 1.81.0-nightly (ba1d7f4a0 2024-06-29)
binary: rustc
commit-hash: ba1d7f4a083e6402679105115ded645512a7aea8
commit-date: 2024-06-29
host: x86_64-unknown-linux-gnu
release: 1.81.0-nightly
LLVM version: 18.1.7

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output

error[E0407]: method `add` is not a member of trait `Add42`
 --> /tmp/icemaker_global_tempdir.xB9oQHak7XZe/rustc_testrunner_tmpdir_reporting.Lp6W2hBmunyv/mvce.rs:6:5
  |
6 | /     fn add<A: ~const Add42>(self) -> Foo {
7 | |         Foo
8 | |     }
  | |_____^ not a member of trait `Add42`

error[E0412]: cannot find type `Foo` in this scope
 --> /tmp/icemaker_global_tempdir.xB9oQHak7XZe/rustc_testrunner_tmpdir_reporting.Lp6W2hBmunyv/mvce.rs:6:38
  |
6 |     fn add<A: ~const Add42>(self) -> Foo {
  |                                      ^^^ not found in this scope

error[E0425]: cannot find value `Foo` in this scope
 --> /tmp/icemaker_global_tempdir.xB9oQHak7XZe/rustc_testrunner_tmpdir_reporting.Lp6W2hBmunyv/mvce.rs:7:9
  |
7 |         Foo
  |         ^^^ not found in this scope

warning: the feature `effects` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.xB9oQHak7XZe/rustc_testrunner_tmpdir_reporting.Lp6W2hBmunyv/mvce.rs:1:30
  |
1 | #![feature(const_trait_impl, effects)]
  |                              ^^^^^^^
  |
  = note: see issue #102090 <https://github.com/rust-lang/rust/issues/102090> for more information
  = note: `#[warn(incomplete_features)]` on by default

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.xB9oQHak7XZe/rustc_testrunner_tmpdir_reporting.Lp6W2hBmunyv/mvce.rs:9:2
  |
9 | }
  |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.xB9oQHak7XZe/rustc_testrunner_tmpdir_reporting.Lp6W2hBmunyv/mvce.rs`

error: const `impl` for trait `Add42` which is not marked with `#[const_trait]`
 --> /tmp/icemaker_global_tempdir.xB9oQHak7XZe/rustc_testrunner_tmpdir_reporting.Lp6W2hBmunyv/mvce.rs:5:12
  |
3 | trait Add42 {}
  | - help: mark `Add42` as const: `#[const_trait]`
4 |
5 | impl const Add42 for () {
  |            ^^^^^
  |
  = note: marking a trait with `#[const_trait]` ensures all default method bodies are `const`
  = note: adding a non-const method body in the future would be a breaking change

error: `~const` can only be applied to `#[const_trait]` traits
 --> /tmp/icemaker_global_tempdir.xB9oQHak7XZe/rustc_testrunner_tmpdir_reporting.Lp6W2hBmunyv/mvce.rs:6:22
  |
6 |     fn add<A: ~const Add42>(self) -> Foo {
  |                      ^^^^^

thread 'rustc' panicked at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/compiler/rustc_middle/src/ty/util.rs:909:22:
ConstContext::Maybe must have host effect param
stack backtrace:
   0:     0x78ac0a3922b5 - std::backtrace_rs::backtrace::libunwind::trace::h9fec972da723f824
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/../../backtrace/src/backtrace/libunwind.rs:116:5
   1:     0x78ac0a3922b5 - std::backtrace_rs::backtrace::trace_unsynchronized::h6750dc8e20aabcad
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x78ac0a3922b5 - std::sys::backtrace::_print_fmt::h112c52e5e2edb557
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/sys/backtrace.rs:68:5
   3:     0x78ac0a3922b5 - <std::sys::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h4713d06d34163f46
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/sys/backtrace.rs:44:22
   4:     0x78ac0a3e1d9b - core::fmt::rt::Argument::fmt::h919dfde74ebabb2a
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/core/src/fmt/rt.rs:173:76
   5:     0x78ac0a3e1d9b - core::fmt::write::h63ad278710fcf618
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/core/src/fmt/mod.rs:1174:21
   6:     0x78ac0a386e9f - std::io::Write::write_fmt::h48f75cc65a268f9a
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/io/mod.rs:1835:15
   7:     0x78ac0a39208e - std::sys::backtrace::_print::ha47bd77a3336440c
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/sys/backtrace.rs:47:5
   8:     0x78ac0a39208e - std::sys::backtrace::print::hd71c23c2433456bf
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/sys/backtrace.rs:34:9
   9:     0x78ac0a3949d9 - std::panicking::default_hook::{{closure}}::ha7861419c6fed626
  10:     0x78ac0a39477c - std::panicking::default_hook::hdb522e40b65d9458
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/panicking.rs:292:9
  11:     0x78ac06bb18a0 - std[ee1287dda0decb26]::panicking::update_hook::<alloc[ebf157a0a0183114]::boxed::Box<rustc_driver_impl[b3016c550210facb]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x78ac0a3952af - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h8a54893ded3fcd8c
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/alloc/src/boxed.rs:2078:9
  13:     0x78ac0a3952af - std::panicking::rust_panic_with_hook::h79c7320e6dd14ff0
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/panicking.rs:804:13
  14:     0x78ac0a394ed7 - std::panicking::begin_panic_handler::{{closure}}::h6bf6d623eeb925ff
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/panicking.rs:670:13
  15:     0x78ac0a392779 - std::sys::backtrace::__rust_end_short_backtrace::hae9fda2e5a3f99dc
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/sys/backtrace.rs:171:18
  16:     0x78ac0a394bb4 - rust_begin_unwind
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/panicking.rs:661:5
  17:     0x78ac0a3de353 - core::panicking::panic_fmt::h1a6b0ab626f31f34
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/core/src/panicking.rs:74:14
  18:     0x78ac0a3de18b - core::panicking::panic_display::h5ac03becd5683664
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/core/src/panicking.rs:264:5
  19:     0x78ac0a3de18b - core::option::expect_failed::h9ec31866d38db7c4
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/core/src/option.rs:2023:5
  20:     0x78ac084cf6ae - <dyn rustc_hir_analysis[190a10ac9c7209da]::hir_ty_lowering::HirTyLowerer>::lower_poly_trait_ref
  21:     0x78ac084c680a - rustc_hir_analysis[190a10ac9c7209da]::collect::predicates_of::gather_explicit_predicates_of
  22:     0x78ac084c43dc - rustc_query_impl[e193fcc3be99e64a]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[e193fcc3be99e64a]::query_impl::explicit_predicates_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[375bbde5f17fb8ea]::query::erase::Erased<[u8; 32usize]>>
  23:     0x78ac084bee85 - rustc_query_system[ab5481f6c869ba71]::query::plumbing::try_execute_query::<rustc_query_impl[e193fcc3be99e64a]::DynamicConfig<rustc_query_system[ab5481f6c869ba71]::query::caches::DefIdCache<rustc_middle[375bbde5f17fb8ea]::query::erase::Erased<[u8; 32usize]>>, false, false, false>, rustc_query_impl[e193fcc3be99e64a]::plumbing::QueryCtxt, false>
  24:     0x78ac084beb23 - rustc_query_impl[e193fcc3be99e64a]::query_impl::explicit_predicates_of::get_query_non_incr::__rust_end_short_backtrace
  25:     0x78ac084bfb1e - rustc_hir_analysis[190a10ac9c7209da]::collect::predicates_defined_on
  26:     0x78ac084bfa2d - rustc_query_impl[e193fcc3be99e64a]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[e193fcc3be99e64a]::query_impl::predicates_defined_on::dynamic_query::{closure#2}::{closure#0}, rustc_middle[375bbde5f17fb8ea]::query::erase::Erased<[u8; 32usize]>>
  27:     0x78ac084bee57 - rustc_query_system[ab5481f6c869ba71]::query::plumbing::try_execute_query::<rustc_query_impl[e193fcc3be99e64a]::DynamicConfig<rustc_query_system[ab5481f6c869ba71]::query::caches::DefIdCache<rustc_middle[375bbde5f17fb8ea]::query::erase::Erased<[u8; 32usize]>>, false, false, false>, rustc_query_impl[e193fcc3be99e64a]::plumbing::QueryCtxt, false>
  28:     0x78ac084be927 - rustc_query_impl[e193fcc3be99e64a]::query_impl::predicates_defined_on::get_query_non_incr::__rust_end_short_backtrace
  29:     0x78ac084bddd5 - rustc_hir_analysis[190a10ac9c7209da]::collect::predicates_of::predicates_of
  30:     0x78ac084bdcd1 - rustc_query_impl[e193fcc3be99e64a]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[e193fcc3be99e64a]::query_impl::predicates_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[375bbde5f17fb8ea]::query::erase::Erased<[u8; 32usize]>>
  31:     0x78ac084bee6e - rustc_query_system[ab5481f6c869ba71]::query::plumbing::try_execute_query::<rustc_query_impl[e193fcc3be99e64a]::DynamicConfig<rustc_query_system[ab5481f6c869ba71]::query::caches::DefIdCache<rustc_middle[375bbde5f17fb8ea]::query::erase::Erased<[u8; 32usize]>>, false, false, false>, rustc_query_impl[e193fcc3be99e64a]::plumbing::QueryCtxt, false>
  32:     0x78ac084bea23 - rustc_query_impl[e193fcc3be99e64a]::query_impl::predicates_of::get_query_non_incr::__rust_end_short_backtrace
  33:     0x78ac084ac05c - <rustc_hir_analysis[190a10ac9c7209da]::collect::CollectItemTypesVisitor as rustc_hir[9cb815a008d04811]::intravisit::Visitor>::visit_impl_item
  34:     0x78ac05a3654b - rustc_hir_analysis[190a10ac9c7209da]::check::wfcheck::check_well_formed
  35:     0x78ac08639c69 - rustc_query_impl[e193fcc3be99e64a]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[e193fcc3be99e64a]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[375bbde5f17fb8ea]::query::erase::Erased<[u8; 1usize]>>
  36:     0x78ac08639ef5 - rustc_query_system[ab5481f6c869ba71]::query::plumbing::try_execute_query::<rustc_query_impl[e193fcc3be99e64a]::DynamicConfig<rustc_query_system[ab5481f6c869ba71]::query::caches::VecCache<rustc_hir[9cb815a008d04811]::hir_id::OwnerId, rustc_middle[375bbde5f17fb8ea]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[e193fcc3be99e64a]::plumbing::QueryCtxt, false>
  37:     0x78ac08639c46 - rustc_query_impl[e193fcc3be99e64a]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  38:     0x78ac0863aab4 - rustc_hir_analysis[190a10ac9c7209da]::check::wfcheck::check_mod_type_wf
  39:     0x78ac0863a759 - rustc_query_impl[e193fcc3be99e64a]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[e193fcc3be99e64a]::query_impl::check_mod_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[375bbde5f17fb8ea]::query::erase::Erased<[u8; 1usize]>>
  40:     0x78ac08e26778 - rustc_query_system[ab5481f6c869ba71]::query::plumbing::try_execute_query::<rustc_query_impl[e193fcc3be99e64a]::DynamicConfig<rustc_query_system[ab5481f6c869ba71]::query::caches::DefaultCache<rustc_span[a32535cd2922901f]::def_id::LocalModDefId, rustc_middle[375bbde5f17fb8ea]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[e193fcc3be99e64a]::plumbing::QueryCtxt, false>
  41:     0x78ac08e26527 - rustc_query_impl[e193fcc3be99e64a]::query_impl::check_mod_type_wf::get_query_non_incr::__rust_end_short_backtrace
  42:     0x78ac08242523 - rustc_hir_analysis[190a10ac9c7209da]::check_crate
  43:     0x78ac08745455 - rustc_interface[ab25a569cec44e98]::passes::analysis
  44:     0x78ac08745015 - rustc_query_impl[e193fcc3be99e64a]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[e193fcc3be99e64a]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[375bbde5f17fb8ea]::query::erase::Erased<[u8; 1usize]>>
  45:     0x78ac08e1c2e5 - rustc_query_system[ab5481f6c869ba71]::query::plumbing::try_execute_query::<rustc_query_impl[e193fcc3be99e64a]::DynamicConfig<rustc_query_system[ab5481f6c869ba71]::query::caches::SingleCache<rustc_middle[375bbde5f17fb8ea]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[e193fcc3be99e64a]::plumbing::QueryCtxt, false>
  46:     0x78ac08e1c04f - rustc_query_impl[e193fcc3be99e64a]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  47:     0x78ac08d5037f - rustc_interface[ab25a569cec44e98]::interface::run_compiler::<core[a458eee17fffdec1]::result::Result<(), rustc_span[a32535cd2922901f]::ErrorGuaranteed>, rustc_driver_impl[b3016c550210facb]::run_compiler::{closure#0}>::{closure#1}
  48:     0x78ac08cdc649 - std[ee1287dda0decb26]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[ab25a569cec44e98]::util::run_in_thread_with_globals<rustc_interface[ab25a569cec44e98]::util::run_in_thread_pool_with_globals<rustc_interface[ab25a569cec44e98]::interface::run_compiler<core[a458eee17fffdec1]::result::Result<(), rustc_span[a32535cd2922901f]::ErrorGuaranteed>, rustc_driver_impl[b3016c550210facb]::run_compiler::{closure#0}>::{closure#1}, core[a458eee17fffdec1]::result::Result<(), rustc_span[a32535cd2922901f]::ErrorGuaranteed>>::{closure#0}, core[a458eee17fffdec1]::result::Result<(), rustc_span[a32535cd2922901f]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[a458eee17fffdec1]::result::Result<(), rustc_span[a32535cd2922901f]::ErrorGuaranteed>>
  49:     0x78ac08cdc3fa - <<std[ee1287dda0decb26]::thread::Builder>::spawn_unchecked_<rustc_interface[ab25a569cec44e98]::util::run_in_thread_with_globals<rustc_interface[ab25a569cec44e98]::util::run_in_thread_pool_with_globals<rustc_interface[ab25a569cec44e98]::interface::run_compiler<core[a458eee17fffdec1]::result::Result<(), rustc_span[a32535cd2922901f]::ErrorGuaranteed>, rustc_driver_impl[b3016c550210facb]::run_compiler::{closure#0}>::{closure#1}, core[a458eee17fffdec1]::result::Result<(), rustc_span[a32535cd2922901f]::ErrorGuaranteed>>::{closure#0}, core[a458eee17fffdec1]::result::Result<(), rustc_span[a32535cd2922901f]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[a458eee17fffdec1]::result::Result<(), rustc_span[a32535cd2922901f]::ErrorGuaranteed>>::{closure#2} as core[a458eee17fffdec1]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  50:     0x78ac0a39f10b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hc6d49d49179bb535
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/alloc/src/boxed.rs:2064:9
  51:     0x78ac0a39f10b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h7270f16d3abba4aa
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/alloc/src/boxed.rs:2064:9
  52:     0x78ac0a39f10b - std::sys::pal::unix::thread::Thread::new::thread_start::h3929f25d671aa35f
                               at /rustc/ba1d7f4a083e6402679105115ded645512a7aea8/library/std/src/sys/pal/unix/thread.rs:108:17
  53:     0x78ac036a6ded - <unknown>
  54:     0x78ac0372a0dc - <unknown>
  55:                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: rustc 1.81.0-nightly (ba1d7f4a0 2024-06-29) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [explicit_predicates_of] computing explicit predicates of `<impl at /tmp/icemaker_global_tempdir.xB9oQHak7XZe/rustc_testrunner_tmpdir_reporting.Lp6W2hBmunyv/mvce.rs:5:1: 5:24>::add`
#1 [predicates_defined_on] computing predicates of `<impl at /tmp/icemaker_global_tempdir.xB9oQHak7XZe/rustc_testrunner_tmpdir_reporting.Lp6W2hBmunyv/mvce.rs:5:1: 5:24>::add`
end of query stack
error: aborting due to 6 previous errors; 1 warning emitted

Some errors have detailed explanations: E0407, E0412, E0425, E0601.
For more information about an error, try `rustc --explain E0407`.

@rustbot label +F-const_trait_impl +F-effects +F-generic_arg_infer +F-generic_const_exprs

[GrigorenkoPV]

searched nightlies: from nightly-2023-04-15 to nightly-2024-06-30
regressed nightly: nightly-2024-06-30
searched commit range: e9e6e2e...ba1d7f4
regressed commit: ba1d7f4 (#120639)