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ICE: `When translating generic parameters from `..` to `..`, the expected specialization failed to hold` #118987

Open matthiaskrgr opened 9 months ago

matthiaskrgr commented 9 months ago

auto-reduced (treereduce-rust):

#![feature(specialization)] //~ WARN the feature `specialization` is incomplete

trait Assoc {
    type Output;
}

default impl<T: Clone> Assoc for T {
    type Output = bool;
}

impl Assoc for u8 {}

trait Foo {}

impl Foo for <u8 as Assoc>::Output {}
impl Foo for <u16 as Assoc>::Output {}

original:

// run-pass

// Test that impls on projected self types can resolve overlap, even when the
// projections involve specialization, so long as the associated type is
// provided by the most specialized impl.

#![feature(specialization)] //~ WARN the feature `specialization` is incomplete

trait Assoc {
    type Output;
}

default impl<T:Clone> Assoc for T {
    type Output = bool;
}

impl Assoc for u8 { type Assoc = u8; }
impl Assoc for u16 { type Output = u16; }

trait Foo {}
impl Assoc for u32 {}
impl Foo for <u8 as Assoc>::Output {}
impl Foo for <u16 as Assoc>::Output {}

fn main() {}

Version information

rustc 1.76.0-nightly (d253bf61a 2023-12-15)
binary: rustc
commit-hash: d253bf61ad38a59cc579aee688f81a06c31283d3
commit-date: 2023-12-15
host: x86_64-unknown-linux-gnu
release: 1.76.0-nightly
LLVM version: 17.0.6

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

Program output

``` warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes --> /tmp/icemaker_global_tempdir.YmODNJIFWMvh/rustc_testrunner_tmpdir_reporting.mIkKiuxcepa6/mvce.rs:1:12 | 1 | #![feature(specialization)] //~ WARN the feature `specialization` is incomplete | ^^^^^^^^^^^^^^ | = note: see issue #31844 for more information = help: consider using `min_specialization` instead, which is more stable and complete = note: `#[warn(incomplete_features)]` on by default error[E0601]: `main` function not found in crate `mvce` --> /tmp/icemaker_global_tempdir.YmODNJIFWMvh/rustc_testrunner_tmpdir_reporting.mIkKiuxcepa6/mvce.rs:16:39 | 16 | impl Foo for ::Output {} | ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.YmODNJIFWMvh/rustc_testrunner_tmpdir_reporting.mIkKiuxcepa6/mvce.rs` error: internal compiler error: compiler/rustc_trait_selection/src/traits/specialize/mod.rs:123:21: When translating substitutions from DefId(0:8 ~ mvce[0e9d]::{impl#1}) to DefId(0:5 ~ mvce[0e9d]::{impl#0}), the expected specialization failed to hold thread 'rustc' panicked at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/compiler/rustc_errors/src/lib.rs:1119:75: Box stack backtrace: 0: 0x7f146c02d45c - std::backtrace_rs::backtrace::libunwind::trace::hd6103882acf895e3 at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5 1: 0x7f146c02d45c - std::backtrace_rs::backtrace::trace_unsynchronized::h8bf8e05e9006d12a at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5 2: 0x7f146c02d45c - std::sys_common::backtrace::_print_fmt::h40fa413ec9439832 at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/std/src/sys_common/backtrace.rs:68:5 3: 0x7f146c02d45c - ::fmt::h5055b8322c3eecd3 at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/std/src/sys_common/backtrace.rs:44:22 4: 0x7f146c080510 - core::fmt::rt::Argument::fmt::h142c2cad35d6896a at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/core/src/fmt/rt.rs:142:9 5: 0x7f146c080510 - core::fmt::write::hd72f8a00b68449f5 at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/core/src/fmt/mod.rs:1120:17 6: 0x7f146c0212bf - std::io::Write::write_fmt::h1bcd670a0cd9a7ff at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/std/src/io/mod.rs:1810:15 7: 0x7f146c02d244 - std::sys_common::backtrace::_print::h579af4e2f431a26b at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/std/src/sys_common/backtrace.rs:47:5 8: 0x7f146c02d244 - std::sys_common::backtrace::print::hdb76c2f48b3f9ac2 at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/std/src/sys_common/backtrace.rs:34:9 9: 0x7f146c02ff47 - std::panicking::default_hook::{{closure}}::hb2313c1cb20e0e8d 10: 0x7f146c02fcaf - std::panicking::default_hook::h0c0e9cb7313537d7 at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/std/src/panicking.rs:292:9 11: 0x7f1468d3f330 - std[90fcdab509e9b154]::panicking::update_hook::>::{closure#0} 12: 0x7f146c030688 - as core::ops::function::Fn>::call::h0f5771c93d1f75ce at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/alloc/src/boxed.rs:2029:9 13: 0x7f146c030688 - std::panicking::rust_panic_with_hook::h4edda63d730d17fc at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/std/src/panicking.rs:783:13 14: 0x7f1468d773b4 - std[90fcdab509e9b154]::panicking::begin_panic::::{closure#0} 15: 0x7f1468d73846 - std[90fcdab509e9b154]::sys_common::backtrace::__rust_end_short_backtrace::::{closure#0}, !> 16: 0x7f1468d6eea6 - std[90fcdab509e9b154]::panicking::begin_panic:: 17: 0x7f1468d82558 - ::diagnostic_builder_emit_producing_guarantee 18: 0x7f1469163a15 - ::bug:: 19: 0x7f14691fe5fd - rustc_middle[17eaf787359ec706]::util::bug::opt_span_bug_fmt::::{closure#0} 20: 0x7f14691e7f0a - rustc_middle[17eaf787359ec706]::ty::context::tls::with_opt::::{closure#0}, !>::{closure#0} 21: 0x7f14691e7d88 - rustc_middle[17eaf787359ec706]::ty::context::tls::with_context_opt::::{closure#0}, !>::{closure#0}, !> 22: 0x7f146715b670 - rustc_middle[17eaf787359ec706]::util::bug::bug_fmt 23: 0x7f146a3b9f90 - rustc_trait_selection[2323e8e34cf002d2]::traits::specialize::translate_args_with_cause:: 24: 0x7f146a2a9347 - rustc_trait_selection[2323e8e34cf002d2]::traits::project::opt_normalize_projection_type 25: 0x7f146a2a5f9e - >::fold_ty 26: 0x7f146a95b95c - rustc_trait_selection[2323e8e34cf002d2]::traits::project::normalize_with_depth_to::::{closure#0} 27: 0x7f146a95ae43 - rustc_trait_selection[2323e8e34cf002d2]::traits::coherence::fresh_impl_header_normalized 28: 0x7f146a959108 - rustc_trait_selection[2323e8e34cf002d2]::traits::coherence::overlap 29: 0x7f146a76e9f3 - ::insert 30: 0x7f146a76e07b - ::insert 31: 0x7f146aaa6d8a - rustc_trait_selection[2323e8e34cf002d2]::traits::specialize::specialization_graph_provider 32: 0x7f146aaa67b2 - rustc_query_impl[43baca739a647e2b]::plumbing::__rust_begin_short_backtrace::> 33: 0x7f146a0811d4 - rustc_query_system[f7d04bba5a359203]::query::plumbing::try_execute_query::>, false, false, false>, rustc_query_impl[43baca739a647e2b]::plumbing::QueryCtxt, false> 34: 0x7f146a4220de - rustc_query_impl[43baca739a647e2b]::query_impl::specialization_graph_of::get_query_non_incr::__rust_end_short_backtrace 35: 0x7f146a1ec291 - rustc_hir_analysis[521878d46db95bb1]::coherence::coherent_trait 36: 0x7f146a1ec16f - rustc_query_impl[43baca739a647e2b]::plumbing::__rust_begin_short_backtrace::> 37: 0x7f146a9832fd - rustc_query_system[f7d04bba5a359203]::query::plumbing::try_execute_query::>, false, false, false>, rustc_query_impl[43baca739a647e2b]::plumbing::QueryCtxt, false> 38: 0x7f146a98308d - rustc_query_impl[43baca739a647e2b]::query_impl::coherent_trait::get_query_non_incr::__rust_end_short_backtrace 39: 0x7f146a96e7aa - rustc_hir_analysis[521878d46db95bb1]::check_crate 40: 0x7f146aab0117 - rustc_interface[1819133c53e350af]::passes::analysis 41: 0x7f146aaafd5d - rustc_query_impl[43baca739a647e2b]::plumbing::__rust_begin_short_backtrace::> 42: 0x7f146afa9ff2 - rustc_query_system[f7d04bba5a359203]::query::plumbing::try_execute_query::>, false, false, false>, rustc_query_impl[43baca739a647e2b]::plumbing::QueryCtxt, false> 43: 0x7f146afa9df9 - rustc_query_impl[43baca739a647e2b]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace 44: 0x7f146b045e97 - rustc_interface[1819133c53e350af]::interface::run_compiler::, rustc_driver_impl[c59161498cce3c44]::run_compiler::{closure#0}>::{closure#0} 45: 0x7f146afbceda - std[90fcdab509e9b154]::sys_common::backtrace::__rust_begin_short_backtrace::, rustc_driver_impl[c59161498cce3c44]::run_compiler::{closure#0}>::{closure#0}, core[ea5c17b9bf3f7e3c]::result::Result<(), rustc_span[9c405c0df40bde1a]::ErrorGuaranteed>>::{closure#0}, core[ea5c17b9bf3f7e3c]::result::Result<(), rustc_span[9c405c0df40bde1a]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[ea5c17b9bf3f7e3c]::result::Result<(), rustc_span[9c405c0df40bde1a]::ErrorGuaranteed>> 46: 0x7f146afbcd03 - <::spawn_unchecked_, rustc_driver_impl[c59161498cce3c44]::run_compiler::{closure#0}>::{closure#0}, core[ea5c17b9bf3f7e3c]::result::Result<(), rustc_span[9c405c0df40bde1a]::ErrorGuaranteed>>::{closure#0}, core[ea5c17b9bf3f7e3c]::result::Result<(), rustc_span[9c405c0df40bde1a]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[ea5c17b9bf3f7e3c]::result::Result<(), rustc_span[9c405c0df40bde1a]::ErrorGuaranteed>>::{closure#1} as core[ea5c17b9bf3f7e3c]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0} 47: 0x7f146c03a515 - as core::ops::function::FnOnce>::call_once::h9895702b6be34956 at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/alloc/src/boxed.rs:2015:9 48: 0x7f146c03a515 - as core::ops::function::FnOnce>::call_once::hbd2c76ba009df5db at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/alloc/src/boxed.rs:2015:9 49: 0x7f146c03a515 - std::sys::unix::thread::Thread::new::thread_start::h8bdfca0a04fd1f70 at /rustc/d253bf61ad38a59cc579aee688f81a06c31283d3/library/std/src/sys/unix/thread.rs:108:17 50: 0x7f1465eaa9eb - 51: 0x7f1465f2e7cc - 52: 0x0 - 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 1.76.0-nightly (d253bf61a 2023-12-15) running on x86_64-unknown-linux-gnu query stack during panic: #0 [specialization_graph_of] building specialization graph of trait `Foo` #1 [coherent_trait] coherence checking all impls of trait `Foo` #2 [analysis] running analysis passes on this crate end of query stack error: aborting due to 2 previous errors; 1 warning emitted For more information about this error, try `rustc --explain E0601`. ```

compiler-errors commented 9 months ago

Minimal:

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

trait Assoc {
    type Output;
}

default impl<T: Clone> Assoc for T {
    type Output = bool;
}

impl Assoc for u8 {}

trait Foo {}

impl Foo for <u8 as Assoc>::Output {}
impl Foo for u16 {}

fn main() {}

What the HECK

compiler-errors commented 9 months ago

Oh, lol. This is because we can't select <u8 as Clone> during subst rebasing because it's an unknowable trait ref. Lol.