ICE: min_specilization `When translating substitutions .. the expected specialization failed to hold`

[matthiaskrgr]

Code

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

trait X {}
trait Y: X {}
trait Z {
    type Assoc: Y;
}
struct A<T>(T);

impl<T: X> Z for A<T> {}

impl<T: X> From<<A<T> as Z>::Assoc> for T {}

Meta

rustc --version --verbose:

rustc 1.70.0-nightly (ec2f40c6b 2023-03-30)
binary: rustc
commit-hash: ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b
commit-date: 2023-03-30
host: x86_64-unknown-linux-gnu
release: 1.70.0-nightly
LLVM version: 16.0.0

Error output

<output>

Backtrace

error: internal compiler error: compiler/rustc_trait_selection/src/traits/specialize/mod.rs:104:21: When translating substitutions from DefId(0:13 ~ treereduce[d8c8]::{impl#1}) to DefId(2:2554 ~ core[ad74]::convert::{impl#4}), the expected specialization failed to hold

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/compiler/rustc_errors/src/lib.rs:1644:9
stack backtrace:
   0:     0x7fe921565e8a - std::backtrace_rs::backtrace::libunwind::trace::h0800f724f14b9f23
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7fe921565e8a - std::backtrace_rs::backtrace::trace_unsynchronized::heb729c2b48914e5d
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7fe921565e8a - std::sys_common::backtrace::_print_fmt::hfea18c777a6816a8
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7fe921565e8a - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h5b335f1b57b7cfd3
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7fe9215c9e6f - core::fmt::write::hfc269b47768b84d6
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/core/src/fmt/mod.rs:1254:17
   5:     0x7fe9215589c5 - std::io::Write::write_fmt::h1d662a9c8dd6348d
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/std/src/io/mod.rs:1698:15
   6:     0x7fe921565c55 - std::sys_common::backtrace::_print::h077a497ebae0e284
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7fe921565c55 - std::sys_common::backtrace::print::h4c1bfafb31892c37
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7fe9215688fe - std::panicking::default_hook::{{closure}}::h1d180e0dd97821e1
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/std/src/panicking.rs:269:22
   9:     0x7fe9215686a5 - std::panicking::default_hook::hb57aa318320cb549
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/std/src/panicking.rs:288:9
  10:     0x7fe924884795 - rustc_driver_impl[5ba0129e8085a63c]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7fe9215690f4 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h3b37cd4b5b400fd5
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/alloc/src/boxed.rs:1990:9
  12:     0x7fe9215690f4 - std::panicking::rust_panic_with_hook::h9f9047c578e712fa
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/std/src/panicking.rs:694:13
  13:     0x7fe924db7381 - std[30ef443cf2df054a]::panicking::begin_panic::<rustc_errors[75c985f96908534a]::ExplicitBug>::{closure#0}
  14:     0x7fe924db4456 - std[30ef443cf2df054a]::sys_common::backtrace::__rust_end_short_backtrace::<std[30ef443cf2df054a]::panicking::begin_panic<rustc_errors[75c985f96908534a]::ExplicitBug>::{closure#0}, !>
  15:     0x7fe924d941e6 - std[30ef443cf2df054a]::panicking::begin_panic::<rustc_errors[75c985f96908534a]::ExplicitBug>
  16:     0x7fe924de8b46 - <rustc_errors[75c985f96908534a]::HandlerInner>::bug::<&alloc[241d486ef18b1517]::string::String>
  17:     0x7fe924de8810 - <rustc_errors[75c985f96908534a]::Handler>::bug::<&alloc[241d486ef18b1517]::string::String>
  18:     0x7fe924de3bcb - rustc_middle[a72f0da90161fe4d]::util::bug::opt_span_bug_fmt::<rustc_span[fd4f398dc0172457]::span_encoding::Span>::{closure#0}
  19:     0x7fe924de314a - rustc_middle[a72f0da90161fe4d]::ty::context::tls::with_opt::<rustc_middle[a72f0da90161fe4d]::util::bug::opt_span_bug_fmt<rustc_span[fd4f398dc0172457]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  20:     0x7fe924de3116 - rustc_middle[a72f0da90161fe4d]::ty::context::tls::with_context_opt::<rustc_middle[a72f0da90161fe4d]::ty::context::tls::with_opt<rustc_middle[a72f0da90161fe4d]::util::bug::opt_span_bug_fmt<rustc_span[fd4f398dc0172457]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  21:     0x7fe924de3b16 - rustc_middle[a72f0da90161fe4d]::util::bug::opt_span_bug_fmt::<rustc_span[fd4f398dc0172457]::span_encoding::Span>
  22:     0x7fe922b0a823 - rustc_middle[a72f0da90161fe4d]::util::bug::bug_fmt
  23:     0x7fe922d912e3 - rustc_trait_selection[b0fa191af389ed74]::traits::specialize::translate_substs
  24:     0x7fe923b7319e - rustc_hir_analysis[d7ef42721b387ff3]::impl_wf_check::min_specialization::check_min_specialization
  25:     0x7fe923b70bdb - rustc_hir_analysis[d7ef42721b387ff3]::impl_wf_check::check_mod_impl_wf
  26:     0x7fe923e867d1 - rustc_query_system[c2820fdbf5c6d6ca]::query::plumbing::try_execute_query::<rustc_query_impl[9d23c39401f72dce]::queries::check_mod_impl_wf, rustc_query_impl[9d23c39401f72dce]::plumbing::QueryCtxt>
  27:     0x7fe923e863f9 - <rustc_query_impl[9d23c39401f72dce]::Queries as rustc_middle[a72f0da90161fe4d]::ty::query::QueryEngine>::check_mod_impl_wf
  28:     0x7fe923ce202f - <rustc_session[173a7fb0306a5cb1]::session::Session>::track_errors::<rustc_hir_analysis[d7ef42721b387ff3]::check_crate::{closure#2}, ()>
  29:     0x7fe923cde362 - rustc_hir_analysis[d7ef42721b387ff3]::check_crate
  30:     0x7fe923cd8241 - rustc_interface[415d18af8a4706e7]::passes::analysis
  31:     0x7fe92403bb82 - rustc_query_system[c2820fdbf5c6d6ca]::query::plumbing::try_execute_query::<rustc_query_impl[9d23c39401f72dce]::queries::analysis, rustc_query_impl[9d23c39401f72dce]::plumbing::QueryCtxt>
  32:     0x7fe92403b880 - <rustc_query_impl[9d23c39401f72dce]::Queries as rustc_middle[a72f0da90161fe4d]::ty::query::QueryEngine>::analysis
  33:     0x7fe9239ff79e - <rustc_interface[415d18af8a4706e7]::queries::QueryResult<&rustc_middle[a72f0da90161fe4d]::ty::context::GlobalCtxt>>::enter::<core[ad7470cf32ab1c97]::result::Result<(), rustc_span[fd4f398dc0172457]::ErrorGuaranteed>, rustc_driver_impl[5ba0129e8085a63c]::run_compiler::{closure#1}::{closure#2}::{closure#4}>
  34:     0x7fe9239fe33e - <rustc_interface[415d18af8a4706e7]::interface::Compiler>::enter::<rustc_driver_impl[5ba0129e8085a63c]::run_compiler::{closure#1}::{closure#2}, core[ad7470cf32ab1c97]::result::Result<core[ad7470cf32ab1c97]::option::Option<rustc_interface[415d18af8a4706e7]::queries::Linker>, rustc_span[fd4f398dc0172457]::ErrorGuaranteed>>
  35:     0x7fe9239fc4f1 - rustc_span[fd4f398dc0172457]::with_source_map::<core[ad7470cf32ab1c97]::result::Result<(), rustc_span[fd4f398dc0172457]::ErrorGuaranteed>, rustc_interface[415d18af8a4706e7]::interface::run_compiler<core[ad7470cf32ab1c97]::result::Result<(), rustc_span[fd4f398dc0172457]::ErrorGuaranteed>, rustc_driver_impl[5ba0129e8085a63c]::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
  36:     0x7fe9239fba9f - std[30ef443cf2df054a]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[415d18af8a4706e7]::util::run_in_thread_pool_with_globals<rustc_interface[415d18af8a4706e7]::interface::run_compiler<core[ad7470cf32ab1c97]::result::Result<(), rustc_span[fd4f398dc0172457]::ErrorGuaranteed>, rustc_driver_impl[5ba0129e8085a63c]::run_compiler::{closure#1}>::{closure#0}, core[ad7470cf32ab1c97]::result::Result<(), rustc_span[fd4f398dc0172457]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[ad7470cf32ab1c97]::result::Result<(), rustc_span[fd4f398dc0172457]::ErrorGuaranteed>>
  37:     0x7fe92411934e - <<std[30ef443cf2df054a]::thread::Builder>::spawn_unchecked_<rustc_interface[415d18af8a4706e7]::util::run_in_thread_pool_with_globals<rustc_interface[415d18af8a4706e7]::interface::run_compiler<core[ad7470cf32ab1c97]::result::Result<(), rustc_span[fd4f398dc0172457]::ErrorGuaranteed>, rustc_driver_impl[5ba0129e8085a63c]::run_compiler::{closure#1}>::{closure#0}, core[ad7470cf32ab1c97]::result::Result<(), rustc_span[fd4f398dc0172457]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[ad7470cf32ab1c97]::result::Result<(), rustc_span[fd4f398dc0172457]::ErrorGuaranteed>>::{closure#1} as core[ad7470cf32ab1c97]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  38:     0x7fe9215731d5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h6e08d5234042fb15
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/alloc/src/boxed.rs:1976:9
  39:     0x7fe9215731d5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h2c5056bcb5d46eb1
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/alloc/src/boxed.rs:1976:9
  40:     0x7fe9215731d5 - std::sys::unix::thread::Thread::new::thread_start::hbc95b3c4a4c1dd3a
                               at /rustc/ec2f40c6b04f0e9850dd1f454e8639d319f4ed9b/library/std/src/sys/unix/thread.rs:108:17
  41:     0x7fe92130dbb5 - <unknown>
  42:     0x7fe92138fd90 - <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 (ec2f40c6b 2023-03-30) 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 previous error

[matthiaskrgr]

searched toolchains nightly-2020-03-12 through nightly-2023-03-31

---

Regression in nightly-2020-03-18

---

probably #68970

[matthewjasper]

Without standard library code:

#![feature(min_specialization)]

trait X {}
trait Y: X {}
trait Z {
    type Assoc: Y;
}
struct A<T>(T);

impl<T: X> Z for A<T> {}

trait MyFrom<T> {
    fn from(other: T) -> Self;
}

impl<T> MyFrom<T> for T {
    fn from(other: T) -> T {
        other
    }
}

impl<T: X> MyFrom<<A<T> as Z>::Assoc> for T {}