compiler crash caused by using feature(generic_const_exprs)

[Retamogordo]

This a minimized code that causes the compiler to crash. While the example itself doesn't need the generic_const_exprs feature, the original library uses it and even compiles, but a binary that depends on the library and itself does not include generic_const_exprs feature, causes the exactly same internal compiler error

Code

#![feature(generic_const_exprs)]

use core::marker::PhantomData;

pub const DEFAULT_MAX_INPUT_LEN: usize = 256;

pub trait FooTrait {}

pub struct Foo<const MAX_INPUT_LEN: usize>;

impl<const MAX_INPUT_LEN: usize> FooTrait for Foo<MAX_INPUT_LEN> {}

pub struct Bar<
    const MAX_INPUT_LEN: usize = DEFAULT_MAX_INPUT_LEN,
    PB = Foo<MAX_INPUT_LEN>,
> 
where
    PB: FooTrait,
{
    _pb: PhantomData<PB>,
}

impl<const MAX_INPUT_LEN: usize, PB> Bar<MAX_INPUT_LEN, PB>
where
    PB: FooTrait,
{
    pub fn new() -> Self {
        Self {
            _pb: PhantomData,
        }
    }
}

Meta

rustc 1.70.0-nightly (22f247c6f 2023-03-13)
binary: rustc
commit-hash: 22f247c6f3ed388cb702d01c2ff27da658a8b353
commit-date: 2023-03-13
host: x86_64-unknown-linux-gnu
release: 1.70.0-nightly
LLVM version: 15.0.7

Error output

warning: the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes
 --> src/lib.rs:1:12
  |
1 | #![feature(generic_const_exprs)]
  |            ^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #76560 <https://github.com/rust-lang/rust/issues/76560> for more information
  = note: `#[warn(incomplete_features)]` on by default

error: internal compiler error: compiler/rustc_middle/src/ty/subst.rs:896:9: type parameter `PB/#1` (PB/1) out of range when substituting, substs=[]

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/compiler/rustc_errors/src/lib.rs:1644:9
stack backtrace:
   0:     0x7f88f9ad751a - std::backtrace_rs::backtrace::libunwind::trace::h1ac6254167c780d9
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f88f9ad751a - std::backtrace_rs::backtrace::trace_unsynchronized::hec2af85915e24f36
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f88f9ad751a - std::sys_common::backtrace::_print_fmt::h58a4e3535fcce206
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f88f9ad751a - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h5107e13758b8321c
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f88f9b3ac5e - core::fmt::write::h2e851dc027730d81
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/core/src/fmt/mod.rs:1232:17
   5:     0x7f88f9aca375 - std::io::Write::write_fmt::hca00074de9f85084
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/std/src/io/mod.rs:1684:15
   6:     0x7f88f9ad72e5 - std::sys_common::backtrace::_print::h870053c845cddf24
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7f88f9ad72e5 - std::sys_common::backtrace::print::hb56add862f96c5fd
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7f88f9ada05f - std::panicking::default_hook::{{closure}}::h636d4ba3ff8fdc46
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/std/src/panicking.rs:271:22
   9:     0x7f88f9ad9d9b - std::panicking::default_hook::hf29b58145ee6e43c
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/std/src/panicking.rs:290:9
  10:     0x7f88fcdc90c5 - <rustc_driver_impl[74350ec99973fded]::DEFAULT_HOOK::{closure#0}::{closure#0} as core[2011dc7817943e09]::ops::function::FnOnce<(&core[2011dc7817943e09]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  11:     0x7f88f9ada89d - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h7342d57f33f6634f
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/alloc/src/boxed.rs:2002:9
  12:     0x7f88f9ada89d - std::panicking::rust_panic_with_hook::hbf9ef936d990c16f
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/std/src/panicking.rs:696:13
  13:     0x7f88fd3335b1 - std[1337fb43929788f1]::panicking::begin_panic::<rustc_errors[9dbe0d28acf3471b]::ExplicitBug>::{closure#0}
  14:     0x7f88fd32ea36 - std[1337fb43929788f1]::sys_common::backtrace::__rust_end_short_backtrace::<std[1337fb43929788f1]::panicking::begin_panic<rustc_errors[9dbe0d28acf3471b]::ExplicitBug>::{closure#0}, !>
  15:     0x7f88fd3b3e86 - std[1337fb43929788f1]::panicking::begin_panic::<rustc_errors[9dbe0d28acf3471b]::ExplicitBug>
  16:     0x7f88fd37ffe6 - std[1337fb43929788f1]::panic::panic_any::<rustc_errors[9dbe0d28acf3471b]::ExplicitBug>
  17:     0x7f88fd37c866 - <rustc_errors[9dbe0d28acf3471b]::HandlerInner>::bug::<&alloc[b7ae3602ac956de8]::string::String>
  18:     0x7f88fd37c530 - <rustc_errors[9dbe0d28acf3471b]::Handler>::bug::<&alloc[b7ae3602ac956de8]::string::String>
  19:     0x7f88fd36895b - rustc_middle[eaae5d2a0b8f0144]::util::bug::opt_span_bug_fmt::<rustc_span[18b84908941c7cdf]::span_encoding::Span>::{closure#0}
  20:     0x7f88fd3673ba - rustc_middle[eaae5d2a0b8f0144]::ty::context::tls::with_opt::<rustc_middle[eaae5d2a0b8f0144]::util::bug::opt_span_bug_fmt<rustc_span[18b84908941c7cdf]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  21:     0x7f88fd367386 - rustc_middle[eaae5d2a0b8f0144]::ty::context::tls::with_context_opt::<rustc_middle[eaae5d2a0b8f0144]::ty::context::tls::with_opt<rustc_middle[eaae5d2a0b8f0144]::util::bug::opt_span_bug_fmt<rustc_span[18b84908941c7cdf]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  22:     0x7f88fd3688a6 - rustc_middle[eaae5d2a0b8f0144]::util::bug::opt_span_bug_fmt::<rustc_span[18b84908941c7cdf]::span_encoding::Span>
  23:     0x7f88fb4a25c3 - rustc_middle[eaae5d2a0b8f0144]::util::bug::bug_fmt
  24:     0x7f88fd33d6ae - <rustc_middle[eaae5d2a0b8f0144]::ty::subst::SubstFolder>::type_param_out_of_range
  25:     0x7f88faddc725 - <rustc_middle[eaae5d2a0b8f0144]::ty::subst::SubstFolder as rustc_type_ir[65f3a8acf733f7d2]::fold::FallibleTypeFolder<rustc_middle[eaae5d2a0b8f0144]::ty::context::TyCtxt>>::try_fold_ty
  26:     0x7f88faf09184 - <rustc_middle[eaae5d2a0b8f0144]::ty::generics::GenericPredicates>::instantiate_into
  27:     0x7f88fb4aec05 - <rustc_trait_selection[88fe5da1728944e3]::traits::wf::WfPredicates>::nominal_obligations_inner
  28:     0x7f88fb47b284 - <rustc_trait_selection[88fe5da1728944e3]::traits::wf::WfPredicates>::compute
  29:     0x7f88fb471901 - rustc_trait_selection[88fe5da1728944e3]::traits::wf::obligations
  30:     0x7f88fb45871c - <rustc_trait_selection[88fe5da1728944e3]::traits::fulfill::FulfillProcessor as rustc_data_structures[75b47a18491287a9]::obligation_forest::ObligationProcessor>::process_obligation
  31:     0x7f88fb455b44 - <rustc_data_structures[75b47a18491287a9]::obligation_forest::ObligationForest<rustc_trait_selection[88fe5da1728944e3]::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection[88fe5da1728944e3]::traits::fulfill::FulfillProcessor>
  32:     0x7f88fb993e70 - <rustc_trait_selection[88fe5da1728944e3]::traits::engine::ObligationCtxt>::select_all_or_error
  33:     0x7f88fbc93602 - rustc_hir_analysis[80836a89449caedf]::check::wfcheck::check_type_defn
  34:     0x7f88fbc71105 - rustc_hir_analysis[80836a89449caedf]::check::wfcheck::check_well_formed
  35:     0x7f88fb239d14 - rustc_query_system[f881c7f40ee7dcf0]::query::plumbing::try_execute_query::<rustc_query_impl[eb95ff51c492efdd]::queries::check_well_formed, rustc_query_impl[eb95ff51c492efdd]::plumbing::QueryCtxt>
  36:     0x7f88fc5aa256 - rustc_query_system[f881c7f40ee7dcf0]::query::plumbing::force_query::<rustc_query_impl[eb95ff51c492efdd]::queries::check_well_formed, rustc_query_impl[eb95ff51c492efdd]::plumbing::QueryCtxt>
  37:     0x7f88fc5aa10c - <rustc_query_impl[eb95ff51c492efdd]::plumbing::query_callback<rustc_query_impl[eb95ff51c492efdd]::queries::check_well_formed>::{closure#0} as core[2011dc7817943e09]::ops::function::FnOnce<(rustc_middle[eaae5d2a0b8f0144]::ty::context::TyCtxt, rustc_query_system[f881c7f40ee7dcf0]::dep_graph::dep_node::DepNode<rustc_middle[eaae5d2a0b8f0144]::dep_graph::dep_node::DepKind>)>>::call_once
  38:     0x7f88faf02bcc - <rustc_query_system[f881c7f40ee7dcf0]::dep_graph::graph::DepGraphData<rustc_middle[eaae5d2a0b8f0144]::dep_graph::dep_node::DepKind>>::try_mark_previous_green::<rustc_query_impl[eb95ff51c492efdd]::plumbing::QueryCtxt>
  39:     0x7f88fbc46c38 - <rustc_query_system[f881c7f40ee7dcf0]::dep_graph::graph::DepGraph<rustc_middle[eaae5d2a0b8f0144]::dep_graph::dep_node::DepKind>>::try_mark_green::<rustc_query_impl[eb95ff51c492efdd]::plumbing::QueryCtxt>
  40:     0x7f88fc4083a2 - rustc_query_system[f881c7f40ee7dcf0]::query::plumbing::ensure_must_run::<rustc_query_impl[eb95ff51c492efdd]::queries::check_mod_type_wf, rustc_query_impl[eb95ff51c492efdd]::plumbing::QueryCtxt>
  41:     0x7f88fc4081d4 - <rustc_query_impl[eb95ff51c492efdd]::Queries as rustc_middle[eaae5d2a0b8f0144]::ty::query::QueryEngine>::check_mod_type_wf
  42:     0x7f88fb1b9128 - rustc_data_structures[75b47a18491287a9]::sync::par_for_each_in::<&[rustc_hir[ca07edd3831bb6e2]::hir_id::OwnerId], <rustc_middle[eaae5d2a0b8f0144]::hir::map::Map>::par_for_each_module<rustc_hir_analysis[80836a89449caedf]::check_crate::{closure#5}::{closure#0}::{closure#0}>::{closure#0}>
  43:     0x7f88fb1b8fb0 - <rustc_session[a360c2d099171c08]::session::Session>::track_errors::<rustc_hir_analysis[80836a89449caedf]::check_crate::{closure#5}, ()>
  44:     0x7f88fb1b61e0 - rustc_hir_analysis[80836a89449caedf]::check_crate
  45:     0x7f88fb1ac1b2 - rustc_interface[ceda1fd77ec39e1b]::passes::analysis
  46:     0x7f88fc5e7c6d - rustc_query_system[f881c7f40ee7dcf0]::query::plumbing::try_execute_query::<rustc_query_impl[eb95ff51c492efdd]::queries::analysis, rustc_query_impl[eb95ff51c492efdd]::plumbing::QueryCtxt>
  47:     0x7f88fc5e7740 - <rustc_query_impl[eb95ff51c492efdd]::Queries as rustc_middle[eaae5d2a0b8f0144]::ty::query::QueryEngine>::analysis
  48:     0x7f88fc410789 - <rustc_middle[eaae5d2a0b8f0144]::ty::context::GlobalCtxt>::enter::<rustc_driver_impl[74350ec99973fded]::run_compiler::{closure#1}::{closure#2}::{closure#4}, core[2011dc7817943e09]::result::Result<(), rustc_span[18b84908941c7cdf]::ErrorGuaranteed>>
  49:     0x7f88fbffff08 - rustc_span[18b84908941c7cdf]::with_source_map::<core[2011dc7817943e09]::result::Result<(), rustc_span[18b84908941c7cdf]::ErrorGuaranteed>, rustc_interface[ceda1fd77ec39e1b]::interface::run_compiler<core[2011dc7817943e09]::result::Result<(), rustc_span[18b84908941c7cdf]::ErrorGuaranteed>, rustc_driver_impl[74350ec99973fded]::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
  50:     0x7f88fbff716c - std[1337fb43929788f1]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[ceda1fd77ec39e1b]::util::run_in_thread_pool_with_globals<rustc_interface[ceda1fd77ec39e1b]::interface::run_compiler<core[2011dc7817943e09]::result::Result<(), rustc_span[18b84908941c7cdf]::ErrorGuaranteed>, rustc_driver_impl[74350ec99973fded]::run_compiler::{closure#1}>::{closure#0}, core[2011dc7817943e09]::result::Result<(), rustc_span[18b84908941c7cdf]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[2011dc7817943e09]::result::Result<(), rustc_span[18b84908941c7cdf]::ErrorGuaranteed>>
  51:     0x7f88fbff6b9a - <<std[1337fb43929788f1]::thread::Builder>::spawn_unchecked_<rustc_interface[ceda1fd77ec39e1b]::util::run_in_thread_pool_with_globals<rustc_interface[ceda1fd77ec39e1b]::interface::run_compiler<core[2011dc7817943e09]::result::Result<(), rustc_span[18b84908941c7cdf]::ErrorGuaranteed>, rustc_driver_impl[74350ec99973fded]::run_compiler::{closure#1}>::{closure#0}, core[2011dc7817943e09]::result::Result<(), rustc_span[18b84908941c7cdf]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[2011dc7817943e09]::result::Result<(), rustc_span[18b84908941c7cdf]::ErrorGuaranteed>>::{closure#1} as core[2011dc7817943e09]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  52:     0x7f88f9ae4793 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h7e0474dd3b8659fa
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/alloc/src/boxed.rs:1988:9
  53:     0x7f88f9ae4793 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::heb8c41cf543a5c11
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/alloc/src/boxed.rs:1988:9
  54:     0x7f88f9ae4793 - std::sys::unix::thread::Thread::new::thread_start::hc791abe67253fe06
                               at /rustc/22f247c6f3ed388cb702d01c2ff27da658a8b353/library/std/src/sys/unix/thread.rs:108:17
  55:     0x7f88f9991609 - start_thread
                               at /build/glibc-SzIz7B/glibc-2.31/nptl/pthread_create.c:477:8
  56:     0x7f88f98b4133 - clone
                               at /build/glibc-SzIz7B/glibc-2.31/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:95
  57:                0x0 - <unknown>

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 1.70.0-nightly (22f247c6f 2023-03-13) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED]

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

query stack during panic:
#0 [check_well_formed] checking that `Bar` is well-formed
#1 [analysis] running analysis passes on this crate
end of query stack
encountered while trying to mark dependency green: check_well_formed(3cb10481615348b4-30cdf74b78880f65)
encountered while trying to mark dependency green: check_mod_type_wf(3cb10481615348b4-e797e994292788bb)
warning: `compiler-failure` (lib) generated 1 warning
error: could not compile `compiler-failure` (lib); 1 warning emitted

Backtrace

<backtrace>

[workingjubilee]

While the example itself doesn't need the generic_const_exprs feature, the original library uses it and even compiles, but a binary that depends on the library and itself does not include generic_const_exprs feature,

It is a well-known feature, unfortunately, that code may typecheck in isolation but fail to compile when actually instantiated. The type system catches most of these problems on its own (barring bugs in its implementation...), but it is particularly a problem for incomplete features.

[workingjubilee]

I am adding the E-needs-mcve label on instinct: I believe there may be a more-minimal repro, though this is pretty good.

[asquared31415]

Good instinct!

#![allow(incomplete_features)]
#![feature(generic_const_exprs)]

const SOME_CONST: usize = 1;

struct UwU<
    // have a const generic with a default that's from another const item
    // (associated consts work, a const declared in a block here, inline_const, etc)
    const N: usize = SOME_CONST,
    // use the previous const in a type generic
    A = [(); N],
> {
    // here to suppress "unused generic" error if the code stops ICEing
    _x: core::marker::PhantomData<A>,
}

playground

@rustbot label -E-needs-mcve

A small note (though, with background, not surprising): this code also ICEs on stable, after emitting the "feature may not be used". Removing the feature gate makes it compile on stable and nightly.

[asquared31415]

#114317 found another reproducer:

struct A<const B: str = 1, C>;

[gurry]

@rustbot claim

[gurry]

Another reproducer:

const MY_CONST: usize = 1;
struct S<const B: usize = MY_CONST, C>;

[gurry]

Duplicate of #106994

Perhaps we can close this one in favour of that.

[workingjubilee]

sure.