ICE: min_specialization: "When translating substitutions for specialization, the expected specialization failed to hold"

[matthiaskrgr]

Code

#![crate_type = "lib"]
#![feature(min_specialization)]

#[derive(Copy)]
struct S<const N: [f32; N]>([f32; f32N]);

#[derive(Copy)]
struct S<const N: usize>([f32; N]);

Meta

rustc --version --verbose:

rustc 1.70.0-nightly (f15f0ea73 2023-03-04)
binary: rustc
commit-hash: f15f0ea73972786e426732c5b92ba9a904b866c4
commit-date: 2023-03-04
host: x86_64-unknown-linux-gnu
release: 1.70.0-nightly
LLVM version: 15.0.7

Error output

error[E0428]: the name `S` is defined multiple times
 --> b61f5be57812969e152a6c4cfc3e11c8e716c601.rs:8:1
  |
5 | struct S<const N: [f32; N]>([f32; f32N]);
  | ----------------------------------------- previous definition of the type `S` here
...
8 | struct S<const N: usize>([f32; N]);
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `S` redefined here
  |
  = note: `S` must be defined only once in the type namespace of this module

error[E0770]: the type of const parameters must not depend on other generic parameters
 --> b61f5be57812969e152a6c4cfc3e11c8e716c601.rs:5:25
  |
5 | struct S<const N: [f32; N]>([f32; f32N]);
  |                         ^ the type must not depend on the parameter `N`

error[E0425]: cannot find value `f32N` in this scope
 --> b61f5be57812969e152a6c4cfc3e11c8e716c601.rs:5:35
  |
5 | struct S<const N: [f32; N]>([f32; f32N]);
  |                                   ^^^^ not found in this scope

Backtrace

error: internal compiler error: compiler/rustc_trait_selection/src/traits/specialize/mod.rs:103:21: When translating substitutions for specialization, the expected specialization failed to hold

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/compiler/rustc_errors/src/lib.rs:1644:9
stack backtrace:
   0:     0x7f1a1fd6731a - std::backtrace_rs::backtrace::libunwind::trace::h4383e0c48d800fd4
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f1a1fd6731a - std::backtrace_rs::backtrace::trace_unsynchronized::h6816d26f08117b4d
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f1a1fd6731a - std::sys_common::backtrace::_print_fmt::hfa640639b16271d1
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f1a1fd6731a - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h4c6c2e6def629543
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f1a1fdcab6e - core::fmt::write::h2c9efad132a334c1
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/core/src/fmt/mod.rs:1232:17
   5:     0x7f1a1fd5a1c5 - std::io::Write::write_fmt::h814bf5ade5b0eb41
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/std/src/io/mod.rs:1684:15
   6:     0x7f1a1fd670e5 - std::sys_common::backtrace::_print::h4c645f879d3eaa7a
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7f1a1fd670e5 - std::sys_common::backtrace::print::h3e307a47c9a19510
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7f1a1fd69e5f - std::panicking::default_hook::{{closure}}::h3c9ff47c1a2169d5
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/std/src/panicking.rs:271:22
   9:     0x7f1a1fd69b9b - std::panicking::default_hook::hce8f146ffdc07b27
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/std/src/panicking.rs:290:9
  10:     0x7f1a22fca2c5 - <rustc_driver_impl[e33d8e87dcf28fa7]::DEFAULT_HOOK::{closure#0}::{closure#0} as core[c90df6780de66b4]::ops::function::FnOnce<(&core[c90df6780de66b4]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  11:     0x7f1a1fd6a69d - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::hbd4f97d1b3fd7f45
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/alloc/src/boxed.rs:2001:9
  12:     0x7f1a1fd6a69d - std::panicking::rust_panic_with_hook::h0f93e1b62c36cd62
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/std/src/panicking.rs:696:13
  13:     0x7f1a23526d01 - std[9d05f37f2a0d456e]::panicking::begin_panic::<rustc_errors[30477a6b69c2e257]::ExplicitBug>::{closure#0}
  14:     0x7f1a2351f386 - std[9d05f37f2a0d456e]::sys_common::backtrace::__rust_end_short_backtrace::<std[9d05f37f2a0d456e]::panicking::begin_panic<rustc_errors[30477a6b69c2e257]::ExplicitBug>::{closure#0}, !>
  15:     0x7f1a23594d66 - std[9d05f37f2a0d456e]::panicking::begin_panic::<rustc_errors[30477a6b69c2e257]::ExplicitBug>
  16:     0x7f1a23572c06 - std[9d05f37f2a0d456e]::panic::panic_any::<rustc_errors[30477a6b69c2e257]::ExplicitBug>
  17:     0x7f1a2356e666 - <rustc_errors[30477a6b69c2e257]::HandlerInner>::bug::<&alloc[7c217260d604da75]::string::String>
  18:     0x7f1a2356e330 - <rustc_errors[30477a6b69c2e257]::Handler>::bug::<&alloc[7c217260d604da75]::string::String>
  19:     0x7f1a235654db - rustc_middle[cce008c1292a9385]::util::bug::opt_span_bug_fmt::<rustc_span[9d8165e91f6b103d]::span_encoding::Span>::{closure#0}
  20:     0x7f1a23563e2a - rustc_middle[cce008c1292a9385]::ty::context::tls::with_opt::<rustc_middle[cce008c1292a9385]::util::bug::opt_span_bug_fmt<rustc_span[9d8165e91f6b103d]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  21:     0x7f1a23563df6 - rustc_middle[cce008c1292a9385]::ty::context::tls::with_context_opt::<rustc_middle[cce008c1292a9385]::ty::context::tls::with_opt<rustc_middle[cce008c1292a9385]::util::bug::opt_span_bug_fmt<rustc_span[9d8165e91f6b103d]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  22:     0x7f1a23565426 - rustc_middle[cce008c1292a9385]::util::bug::opt_span_bug_fmt::<rustc_span[9d8165e91f6b103d]::span_encoding::Span>
  23:     0x7f1a216deb73 - rustc_middle[cce008c1292a9385]::util::bug::bug_fmt
  24:     0x7f1a21605896 - rustc_trait_selection[6c766aae540ef51f]::traits::specialize::translate_substs
  25:     0x7f1a22355b69 - rustc_hir_analysis[e0a40ec4e05edc38]::impl_wf_check::check_mod_impl_wf
  26:     0x7f1a22651841 - rustc_query_system[637feee9637b99c]::query::plumbing::try_execute_query::<rustc_query_impl[2e65c241cbff84cd]::queries::check_mod_impl_wf, rustc_query_impl[2e65c241cbff84cd]::plumbing::QueryCtxt>
  27:     0x7f1a226513ea - <rustc_query_impl[2e65c241cbff84cd]::Queries as rustc_middle[cce008c1292a9385]::ty::query::QueryEngine>::check_mod_impl_wf
  28:     0x7f1a212e871f - <rustc_middle[cce008c1292a9385]::hir::map::Map>::for_each_module::<rustc_hir_analysis[e0a40ec4e05edc38]::check_crate::{closure#2}::{closure#0}::{closure#0}>
  29:     0x7f1a212e8218 - <rustc_session[1facd9ff6612a9d8]::session::Session>::track_errors::<rustc_hir_analysis[e0a40ec4e05edc38]::check_crate::{closure#2}, ()>
  30:     0x7f1a212e5673 - rustc_hir_analysis[e0a40ec4e05edc38]::check_crate
  31:     0x7f1a212d9a22 - rustc_interface[6a01411731a6f2f2]::passes::analysis
  32:     0x7f1a228291fd - rustc_query_system[637feee9637b99c]::query::plumbing::try_execute_query::<rustc_query_impl[2e65c241cbff84cd]::queries::analysis, rustc_query_impl[2e65c241cbff84cd]::plumbing::QueryCtxt>
  33:     0x7f1a22828eff - <rustc_query_impl[2e65c241cbff84cd]::Queries as rustc_middle[cce008c1292a9385]::ty::query::QueryEngine>::analysis
  34:     0x7f1a226539d6 - <rustc_middle[cce008c1292a9385]::ty::context::GlobalCtxt>::enter::<rustc_driver_impl[e33d8e87dcf28fa7]::run_compiler::{closure#1}::{closure#2}::{closure#4}, core[c90df6780de66b4]::result::Result<(), rustc_span[9d8165e91f6b103d]::ErrorGuaranteed>>
  35:     0x7f1a22229238 - rustc_span[9d8165e91f6b103d]::with_source_map::<core[c90df6780de66b4]::result::Result<(), rustc_span[9d8165e91f6b103d]::ErrorGuaranteed>, rustc_interface[6a01411731a6f2f2]::interface::run_compiler<core[c90df6780de66b4]::result::Result<(), rustc_span[9d8165e91f6b103d]::ErrorGuaranteed>, rustc_driver_impl[e33d8e87dcf28fa7]::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
  36:     0x7f1a222208bc - std[9d05f37f2a0d456e]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[6a01411731a6f2f2]::util::run_in_thread_pool_with_globals<rustc_interface[6a01411731a6f2f2]::interface::run_compiler<core[c90df6780de66b4]::result::Result<(), rustc_span[9d8165e91f6b103d]::ErrorGuaranteed>, rustc_driver_impl[e33d8e87dcf28fa7]::run_compiler::{closure#1}>::{closure#0}, core[c90df6780de66b4]::result::Result<(), rustc_span[9d8165e91f6b103d]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[c90df6780de66b4]::result::Result<(), rustc_span[9d8165e91f6b103d]::ErrorGuaranteed>>
  37:     0x7f1a222202ea - <<std[9d05f37f2a0d456e]::thread::Builder>::spawn_unchecked_<rustc_interface[6a01411731a6f2f2]::util::run_in_thread_pool_with_globals<rustc_interface[6a01411731a6f2f2]::interface::run_compiler<core[c90df6780de66b4]::result::Result<(), rustc_span[9d8165e91f6b103d]::ErrorGuaranteed>, rustc_driver_impl[e33d8e87dcf28fa7]::run_compiler::{closure#1}>::{closure#0}, core[c90df6780de66b4]::result::Result<(), rustc_span[9d8165e91f6b103d]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[c90df6780de66b4]::result::Result<(), rustc_span[9d8165e91f6b103d]::ErrorGuaranteed>>::{closure#1} as core[c90df6780de66b4]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  38:     0x7f1a1fd74593 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h437f2034e21e0804
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/alloc/src/boxed.rs:1987:9
  39:     0x7f1a1fd74593 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h9ba15d2eeb7a9119
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/alloc/src/boxed.rs:1987:9
  40:     0x7f1a1fd74593 - std::sys::unix::thread::Thread::new::thread_start::h41ec441a67c2e320
                               at /rustc/f15f0ea73972786e426732c5b92ba9a904b866c4/library/std/src/sys/unix/thread.rs:108:17
  41:     0x7f1a1fb06bb5 - <unknown>
  42:     0x7f1a1fb88d90 - <unknown>
  43:                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 (f15f0ea73 2023-03-04) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [check_mod_impl_wf] checking that impls are well-formed in top-level module
#1 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 4 previous errors

Some errors have detailed explanations: E0425, E0428, E0770.
For more information about an error, try `rustc --explain E0425`.

[compiler-errors]

Minimal:

#![feature(min_specialization)]

struct S<const N: usize>;
impl<const N: i32> Copy for S<N> {}
impl<const N: usize> Copy for S<N> {}

[compiler-errors]

This regressed in #107965, cc @BoxyUwU.

I'll take a look at this -- I think it has something to do with the overlap check failing (succeeding? failing to detect overlap) because of the new ConstArgHasType obligations needed for S to be WF.

[compiler-errors]

Lol, yeah, the specialization graph considers impl<const N: i32> Copy for S<N> {} to specialize impl<const N: usize> Copy for S<N> {} because the trait refs unify (lol) and the first impl has obligations that are not satisfied by the second, but not vice versa (lol).

I think I'm just gonna delay a bug here, though it may be entertaining to consider returning a real type error when trying to unify two consts with differing types...