/checkout/src/librustc/traits/specialize/mod.rs:201: failed to fully normalize

[zhendongsu]

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

trait X {} 
trait Y : X {} 
trait Z { type Assoc : Y; }

struct A < T > (T);

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

$ RUST_BACKTRACE=full rustc-nightly tmp.rs
error: internal compiler error: /checkout/src/librustc/traits/specialize/mod.rs:201: failed to fully normalize <T as std::convert::From<<A<T> as Z>::Assoc>>: [FulfillmentError(Obligation(predicate=Binder(TraitPredicate(<T as X>)),depth=1),Unimplemented)]

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.21.0-nightly (8c303ed87 2017-08-20) running on i686-unknown-linux-gnu

note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:486:8
stack backtrace:
   0: 0xf756ae9a - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::h80d78ba3b40687b5
                       at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: 0xf7565c22 - std::sys_common::backtrace::_print::h47b9b32fe06dd6eb
                       at /checkout/src/libstd/sys_common/backtrace.rs:71
   2: 0xf7576c7e - std::panicking::default_hook::{{closure}}::h006dcf643a2d1ee4
                       at /checkout/src/libstd/sys_common/backtrace.rs:60
                       at /checkout/src/libstd/panicking.rs:381
   3: 0xf75769ad - std::panicking::default_hook::h1e56c296d63316e2
                       at /checkout/src/libstd/panicking.rs:391
   4: 0xf757719b - std::panicking::rust_panic_with_hook::h218401524ff20a29
                       at /checkout/src/libstd/panicking.rs:611
   5: 0xf5ce3361 - std::panicking::begin_panic::h4938377ed080c909
   6: 0xf5d0103f - rustc_errors::Handler::bug::h4d89c75d22c1017a
   7: 0xf642e3d9 - rustc::session::opt_span_bug_fmt::{{closure}}::h381ad37ab7e154b0
   8: 0xf642e0f6 - rustc::session::opt_span_bug_fmt::h528b45e685201abd
   9: 0xf642dddc - rustc::session::bug_fmt::h1dc99310f401e1e0
  10: 0xf63b3ddc - rustc::infer::InferCtxtBuilder::enter::{{closure}}::h82e8f134f0254b28
  11: 0xf6464abe - rustc::traits::specialize::specializes::h7794bdf6e1e8f332
  12: 0xf646233a - rustc::traits::specialize::specialization_graph::Graph::insert::he7ff6d711ea6fcd9
  13: 0xf6467d55 - rustc::traits::specialize::specialization_graph_provider::ha5176b7326253e05
  14: 0xf6301c7f - rustc::dep_graph::graph::DepGraph::with_task::h0b47e6edc22573aa
  15: 0xf6568418 - rustc::ty::maps::<impl rustc::ty::maps::queries::specialization_graph_of<'tcx>>::try_get::h8fd63e3116cfd952
  16: 0xf6580786 - rustc::ty::maps::TyCtxtAt::specialization_graph_of::he681c442a59e5f1e
  17: 0xf657b36c - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::specialization_graph_of::h548cfa1b93c36d1b
  18: 0xf6eb10af - rustc_typeck::coherence::coherent_trait::he9b367dd38388e4d
  19: 0xf6304088 - rustc::dep_graph::graph::DepGraph::with_task::h52ef919fdecc85b3
  20: 0xf6546422 - rustc::ty::maps::<impl rustc::ty::maps::queries::coherent_trait<'tcx>>::try_get::h2545313871596278
  21: 0xf657a28f - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::coherent_trait::haf1a556d9bf16dd4
  22: 0xf6ebb412 - rustc_typeck::check_crate::{{closure}}::{{closure}}::h556e9f4e5e30732c
  23: 0xf6eb946d - rustc_typeck::check_crate::he7e69726bde9082c
  24: 0xf7692706 - rustc::ty::context::TyCtxt::create_and_enter::h54fe8ddc7b2f2638
  25: 0xf76f8e43 - rustc_driver::driver::compile_input::h36c200773836acf5
  26: 0xf7712575 - rustc_driver::run_compiler::hdf3c0b5b5e4bbadc
  27: 0xf7651caf - std::sys_common::backtrace::__rust_begin_short_backtrace::h9143dfc110593bba
  28: 0xf75b3f82 - __rust_maybe_catch_panic
                       at /checkout/src/libpanic_unwind/lib.rs:98
  29: 0xf7683ae1 - <F as alloc::boxed::FnBox<A>>::call_box::h7d6c81c9ff90eab5
  30: 0xf7575cbb - std::sys::imp::thread::Thread::new::thread_start::h505201887c39140f
                       at /checkout/src/liballoc/boxed.rs:692
                       at /checkout/src/libstd/sys_common/thread.rs:21
                       at /checkout/src/libstd/sys/unix/thread.rs:84
  31: 0xf5c65294 - start_thread
  32: 0xf73fa05d - __clone
  33:        0x0 - <unknown>

rustc 1.21.0-nightly (8c303ed87 2017-08-20)

[mattico]

Had a full debuginfo build lying around so I decided to get a backtrace with line info.

Full Backtrace

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.21.0-dev (d69e9cb15 2017-08-22) running on x86_64-pc-windows-msvc

note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'byte index 41 is not a char boundary; it is inside 'ი' (bytes 40..43) of `fn საჭმელად_გემრიელი_სადილი ( ) -> isize {
`', src\libcore\str\mod.rs:2188:4
stack backtrace:
   0:     0x7ff9a5e7a507 - std::sys::imp::backtrace::unwind_backtrace
                               at C:\Users\matth\Code\Rust\rust\src\libstd\sys\windows\backtrace\mod.rs:65
   1:     0x7ff9a5e665a5 - std::sys_common::backtrace::_print
                               at C:\Users\matth\Code\Rust\rust\src\libstd\sys_common\backtrace.rs:71
   2:     0x7ff9a5e65b25 - std::sys_common::backtrace::print
                               at C:\Users\matth\Code\Rust\rust\src\libstd\sys_common\backtrace.rs:60
   3:     0x7ff9a5e9cad5 - std::panicking::default_hook::{{closure}}
                               at C:\Users\matth\Code\Rust\rust\src\libstd\panicking.rs:381
   4:     0x7ff9a5e9c42c - std::panicking::default_hook
                               at C:\Users\matth\Code\Rust\rust\src\libstd\panicking.rs:391
   5:     0x7ff9a5e9d610 - std::panicking::rust_panic_with_hook
                               at C:\Users\matth\Code\Rust\rust\src\libstd\panicking.rs:611
   6:     0x7ff9a5e9d472 - std::panicking::begin_panic<alloc::string::String>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\panicking.rs:572
   7:     0x7ff9a5e9d22e - std::panicking::begin_panic_fmt
                               at C:\Users\matth\Code\Rust\rust\src\libstd\panicking.rs:522
   8:     0x7ff9a5e9d18a - std::panicking::rust_begin_panic
                               at C:\Users\matth\Code\Rust\rust\src\libstd\panicking.rs:498
   9:     0x7ff9a5efe917 - core::panicking::panic_fmt
                               at C:\Users\matth\Code\Rust\rust\src\libcore\panicking.rs:71
  10:     0x7ff9a5f0d4f4 - core::str::slice_error_fail
                               at C:\Users\matth\Code\Rust\rust\src\libcore\str\mod.rs:2188
  11:     0x7ff9bcef5ca4 - core::str::traits::{{impl}}::index::{{closure}}
                               at C:\Users\matth\Code\Rust\rust\src\libcore\str\mod.rs:1846
  12:     0x7ff9bcec0bce - core::option::Option<&str>::unwrap_or_else<&str,closure>
                               at C:\Users\matth\Code\Rust\rust\src\libcore\option.rs:370
  13:     0x7ff9bcef5c38 - core::str::traits::{{impl}}::index
                               at C:\Users\matth\Code\Rust\rust\src\libcore\str\mod.rs:1846
  14:     0x7ff9bcef5960 - core::str::traits::{{impl}}::index
                               at C:\Users\matth\Code\Rust\rust\src\libcore\str\mod.rs:1620
  15:     0x7ff9bcf4f4d5 - rustc_errors::emitter::EmitterWriter::render_source_line
                               at C:\Users\matth\Code\Rust\rust\src\librustc_errors\emitter.rs:314
  16:     0x7ff9bcf56d11 - rustc_errors::emitter::EmitterWriter::emit_message_default
                               at C:\Users\matth\Code\Rust\rust\src\librustc_errors\emitter.rs:987
  17:     0x7ff9bcf5ad98 - rustc_errors::emitter::EmitterWriter::emit_messages_default
                               at C:\Users\matth\Code\Rust\rust\src\librustc_errors\emitter.rs:1155
  18:     0x7ff9bcf4ba91 - rustc_errors::emitter::{{impl}}::emit
                               at C:\Users\matth\Code\Rust\rust\src\librustc_errors\emitter.rs:75
  19:     0x7ff9bcf4adda - rustc_errors::diagnostic_builder::DiagnosticBuilder::emit
                               at C:\Users\matth\Code\Rust\rust\src\librustc_errors\diagnostic_builder.rs:101
  20:     0x7ff99daebfed - rustc_typeck::check::coercion::CoerceMany<syntax::ptr::P<rustc::hir::Expr>>::coerce_inner<syntax::ptr::P<rustc::hir::Expr>>
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\coercion.rs:1211
  21:     0x7ff99dae9ee9 - rustc_typeck::check::coercion::CoerceMany<syntax::ptr::P<rustc::hir::Expr>>::coerce_forced_unit<syntax::ptr::P<rustc::hir::Expr>>
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\coercion.rs:1066
  22:     0x7ff99dba0bc4 - rustc_typeck::check::{{impl}}::check_block_with_expected::{{closure}}
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:4251
  23:     0x7ff99dba95d7 - rustc_typeck::check::FnCtxt::with_breakable_ctxt<closure,()>
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:4887
  24:     0x7ff99dba0216 - rustc_typeck::check::FnCtxt::check_block_with_expected
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:4218
  25:     0x7ff99db991f8 - rustc_typeck::check::FnCtxt::check_expr_kind
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:3813
  26:     0x7ff99db97d27 - rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_lvalue_pref
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:3436
  27:     0x7ff99db8a9b3 - rustc_typeck::check::FnCtxt::check_expr_with_expectation
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:2717
  28:     0x7ff99db8a931 - rustc_typeck::check::FnCtxt::check_expr_with_hint
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:2711
  29:     0x7ff99db8c81b - rustc_typeck::check::FnCtxt::check_return_expr
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:2851
  30:     0x7ff99db6d87e - rustc_typeck::check::check_fn
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:1034
  31:     0x7ff99db6b841 - rustc_typeck::check::typeck_tables_of::{{closure}}
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:868
  32:     0x7ff99db63a30 - rustc_typeck::check::{{impl}}::enter::{{closure}}<closure,&rustc::ty::context::TypeckTables>
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:595
  33:     0x7ff99d93bebc - rustc::infer::{{impl}}::enter::{{closure}}<closure,&rustc::ty::context::TypeckTables>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\infer\mod.rs:375
  34:     0x7ff99d8fb9a8 - rustc::ty::context::tls::enter::{{closure}}<closure,&rustc::ty::context::TypeckTables>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\context.rs:1262
  35:     0x7ff99d7caca6 - std::thread::local::LocalKey<core::cell::Cell<core::option::Option<(*const rustc::ty::context::tls::ThreadLocalGlobalCtxt, *const rustc::ty::context::tls::ThreadLocalInterners)>>>::try_with<core::cell::Cell<core::option::Option<(*const rustc::ty::context::tls::ThreadLocalGlobalCtxt, *const rustc::ty::context::tls::ThreadLocalInterners)>>,closure,&rustc::ty::context::TypeckTables>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\thread\local.rs:365
  36:     0x7ff99d7c77de - std::thread::local::LocalKey<core::cell::Cell<core::option::Option<(*const rustc::ty::context::tls::ThreadLocalGlobalCtxt, *const rustc::ty::context::tls::ThreadLocalInterners)>>>::with<core::cell::Cell<core::option::Option<(*const rustc::ty::context::tls::ThreadLocalGlobalCtxt, *const rustc::ty::context::tls::ThreadLocalInterners)>>,closure,&rustc::ty::context::TypeckTables>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\thread\local.rs:279
  37:     0x7ff99d8fa93b - rustc::ty::context::tls::enter<closure,&rustc::ty::context::TypeckTables>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\context.rs:1259
  38:     0x7ff99d8f8b54 - rustc::ty::context::GlobalCtxt::enter_local<closure,&rustc::ty::context::TypeckTables>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\context.rs:1073
  39:     0x7ff99d93b581 - rustc::infer::InferCtxtBuilder::enter<closure,&rustc::ty::context::TypeckTables>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\infer\mod.rs:375
  40:     0x7ff99db62d19 - rustc_typeck::check::InheritedBuilder::enter<closure,&rustc::ty::context::TypeckTables>
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:595
  41:     0x7ff99db6b1a0 - rustc_typeck::check::typeck_tables_of
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:852
  42:     0x7ff99af98c21 - rustc::ty::maps::{{impl}}::try_get_with::{{closure}}::run_provider
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:609
  43:     0x7ff99aa3b87f - rustc::dep_graph::graph::DepGraph::with_task<rustc::ty::context::TyCtxt,rustc::hir::def_id::DefId,&rustc::ty::context::TypeckTables>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\dep_graph\graph.rs:125
  44:     0x7ff99af98f0e - rustc::ty::maps::{{impl}}::try_get_with::{{closure}}<fn(&&rustc::ty::context::TypeckTables) -> &rustc::ty::context::TypeckTables,&rustc::ty::context::TypeckTables>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:612
  45:     0x7ff99adf8d5a - rustc::ty::context::TyCtxt::cycle_check<closure,(&rustc::ty::context::TypeckTables, rustc::dep_graph::edges::DepNodeIndex)>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:257
  46:     0x7ff99af9826f - rustc::ty::maps::queries::typeck_tables_of::try_get_with<fn(&&rustc::ty::context::TypeckTables) -> &rustc::ty::context::TypeckTables,&rustc::ty::context::TypeckTables>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:596
  47:     0x7ff99af98fc4 - rustc::ty::maps::queries::typeck_tables_of::try_get
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:629
  48:     0x7ff99aff9df9 - rustc::ty::maps::TyCtxtAt::typeck_tables_of
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:675
  49:     0x7ff99aff2ce4 - rustc::ty::context::TyCtxt::typeck_tables_of
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:668
  50:     0x7ff99db6a104 - rustc_typeck::check::typeck_item_bodies::{{closure}}
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:726
  51:     0x7ff99d964a0f - rustc::session::Session::track_errors<closure,()>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\session\mod.rs:270
  52:     0x7ff99db69fa6 - rustc_typeck::check::typeck_item_bodies
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:724
  53:     0x7ff99af96969 - rustc::ty::maps::{{impl}}::try_get_with::{{closure}}::run_provider
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:609
  54:     0x7ff99aa48b6d - rustc::dep_graph::graph::DepGraph::with_task<rustc::ty::context::TyCtxt,rustc::hir::def_id::CrateNum,core::result::Result<(), rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\dep_graph\graph.rs:125
  55:     0x7ff99af96aca - rustc::ty::maps::{{impl}}::try_get_with::{{closure}}<fn(&core::result::Result<(), rustc::session::CompileIncomplete>) -> core::result::Result<(), rustc::session::CompileIncomplete>,core::result::Result<(), rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:612
  56:     0x7ff99add8ceb - rustc::ty::context::TyCtxt::cycle_check<closure,(core::result::Result<(), rustc::session::CompileIncomplete>, rustc::dep_graph::edges::DepNodeIndex)>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:257
  57:     0x7ff99af952e7 - rustc::ty::maps::queries::typeck_item_bodies::try_get_with<fn(&core::result::Result<(), rustc::session::CompileIncomplete>) -> core::result::Result<(), rustc::session::CompileIncomplete>,core::result::Result<(), rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:596
  58:     0x7ff99af96cf8 - rustc::ty::maps::queries::typeck_item_bodies::try_get
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:629
  59:     0x7ff99aff9b05 - rustc::ty::maps::TyCtxtAt::typeck_item_bodies
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:675
  60:     0x7ff99aff2c3c - rustc::ty::context::TyCtxt::typeck_item_bodies
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\maps.rs:668
  61:     0x7ff99db69eda - rustc_typeck::check::check_item_bodies
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\check\mod.rs:717
  62:     0x7ff99dbf2b8c - rustc_typeck::check_crate::{{closure}}
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\lib.rs:326
  63:     0x7ff99d9375ca - rustc::util::common::time<core::result::Result<(), rustc::session::CompileIncomplete>,closure>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\util\common.rs:48
  64:     0x7ff99dbf2698 - rustc_typeck::check_crate
                               at C:\Users\matth\Code\Rust\rust\src\librustc_typeck\lib.rs:326
  65:     0x7ff9a51deb66 - rustc_driver::driver::phase_3_run_analysis_passes::{{closure}}<closure,core::result::Result<(rustc::session::config::OutputFilenames, rustc_trans::back::write::OngoingCrateTranslation), rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\librustc_driver\driver.rs:1041
  66:     0x7ff9a4f362c4 - rustc::ty::context::tls::enter::{{closure}}<closure,core::result::Result<core::result::Result<(rustc::session::config::OutputFilenames, rustc_trans::back::write::OngoingCrateTranslation), rustc::session::CompileIncomplete>, rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\context.rs:1262
  67:     0x7ff9a4e15066 - std::thread::local::LocalKey<core::cell::Cell<core::option::Option<(*const rustc::ty::context::tls::ThreadLocalGlobalCtxt, *const rustc::ty::context::tls::ThreadLocalInterners)>>>::try_with<core::cell::Cell<core::option::Option<(*const rustc::ty::context::tls::ThreadLocalGlobalCtxt, *const rustc::ty::context::tls::ThreadLocalInterners)>>,closure,core::result::Result<core::result::Result<(rustc::session::config::OutputFilenames, rustc_trans::back::write::OngoingCrateTranslation), rustc::session::CompileIncomplete>, rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\thread\local.rs:365
  68:     0x7ff9a4df5866 - std::thread::local::LocalKey<core::cell::Cell<core::option::Option<(*const rustc::ty::context::tls::ThreadLocalGlobalCtxt, *const rustc::ty::context::tls::ThreadLocalInterners)>>>::with<core::cell::Cell<core::option::Option<(*const rustc::ty::context::tls::ThreadLocalGlobalCtxt, *const rustc::ty::context::tls::ThreadLocalInterners)>>,closure,core::result::Result<core::result::Result<(rustc::session::config::OutputFilenames, rustc_trans::back::write::OngoingCrateTranslation), rustc::session::CompileIncomplete>, rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\thread\local.rs:279
  69:     0x7ff9a4f35a39 - rustc::ty::context::tls::enter<closure,core::result::Result<core::result::Result<(rustc::session::config::OutputFilenames, rustc_trans::back::write::OngoingCrateTranslation), rustc::session::CompileIncomplete>, rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\context.rs:1259
  70:     0x7ff9a4f34fa0 - rustc::ty::context::tls::enter_global::{{closure}}<closure,core::result::Result<core::result::Result<(rustc::session::config::OutputFilenames, rustc_trans::back::write::OngoingCrateTranslation), rustc::session::CompileIncomplete>, rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\context.rs:1246
  71:     0x7ff9a4e04ac2 - std::thread::local::LocalKey<core::cell::Cell<fn(syntax_pos::Span, &mut core::fmt::Formatter) -> core::result::Result<(), core::fmt::Error>>>::try_with<core::cell::Cell<fn(syntax_pos::Span, &mut core::fmt::Formatter) -> core::result::Result<(), core::fmt::Error>>,closure,core::result::Result<core::result::Result<(rustc::session::config::OutputFilenames, rustc_trans::back::write::OngoingCrateTranslation), rustc::session::CompileIncomplete>, rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\thread\local.rs:365
  72:     0x7ff9a4dee4b5 - std::thread::local::LocalKey<core::cell::Cell<fn(syntax_pos::Span, &mut core::fmt::Formatter) -> core::result::Result<(), core::fmt::Error>>>::with<core::cell::Cell<fn(syntax_pos::Span, &mut core::fmt::Formatter) -> core::result::Result<(), core::fmt::Error>>,closure,core::result::Result<core::result::Result<(rustc::session::config::OutputFilenames, rustc_trans::back::write::OngoingCrateTranslation), rustc::session::CompileIncomplete>, rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\thread\local.rs:279
  73:     0x7ff9a4f346d0 - rustc::ty::context::tls::enter_global<closure,core::result::Result<core::result::Result<(rustc::session::config::OutputFilenames, rustc_trans::back::write::OngoingCrateTranslation), rustc::session::CompileIncomplete>, rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\context.rs:1243
  74:     0x7ff9a4f3c417 - rustc::ty::context::TyCtxt::create_and_enter<closure,core::result::Result<core::result::Result<(rustc::session::config::OutputFilenames, rustc_trans::back::write::OngoingCrateTranslation), rustc::session::CompileIncomplete>, rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\librustc\ty\context.rs:1024
  75:     0x7ff9a51d83b3 - rustc_driver::driver::phase_3_run_analysis_passes<closure,core::result::Result<(rustc::session::config::OutputFilenames, rustc_trans::back::write::OngoingCrateTranslation), rustc::session::CompileIncomplete>>
                               at C:\Users\matth\Code\Rust\rust\src\librustc_driver\driver.rs:1010
  76:     0x7ff9a51c627d - rustc_driver::driver::compile_input
                               at C:\Users\matth\Code\Rust\rust\src\librustc_driver\driver.rs:196
  77:     0x7ff9a51f6151 - rustc_driver::run_compiler
                               at C:\Users\matth\Code\Rust\rust\src\librustc_driver\lib.rs:316
  78:     0x7ff9a5205d27 - rustc_driver::main::{{closure}}
                               at C:\Users\matth\Code\Rust\rust\src\librustc_driver\lib.rs:1338
  79:     0x7ff9a51f4f12 - rustc_driver::run::{{closure}}<closure>
                               at C:\Users\matth\Code\Rust\rust\src\librustc_driver\lib.rs:132
  80:     0x7ff9a52053d8 - rustc_driver::monitor::{{closure}}<closure>
                               at C:\Users\matth\Code\Rust\rust\src\librustc_driver\lib.rs:1255
  81:     0x7ff9a4dd8b1e - std::sys_common::backtrace::__rust_begin_short_backtrace<closure,()>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\sys_common\backtrace.rs:136
  82:     0x7ff9a4ddf57e - std::thread::{{impl}}::spawn::{{closure}}::{{closure}}<closure,()>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\thread\mod.rs:394
  83:     0x7ff9a4d6338e - std::panic::{{impl}}::call_once<(),closure>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\panic.rs:296
  84:     0x7ff9a4ddfb6b - std::panicking::try::do_call<std::panic::AssertUnwindSafe<closure>,()>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\panicking.rs:480
  85:     0x7ff9a5ea6272 - panic_unwind::__rust_start_panic
  86:     0x7ff9a5ea614f - panic_unwind::__rust_maybe_catch_panic
                               at C:\Users\matth\Code\Rust\rust\src\libpanic_unwind\lib.rs:98
  87:     0x7ff9a4ddf9da - std::panicking::try<(),std::panic::AssertUnwindSafe<closure>>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\panicking.rs:459
  88:     0x7ff9a4ddebe5 - std::panic::catch_unwind<std::panic::AssertUnwindSafe<closure>,()>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\panic.rs:361
  89:     0x7ff9a4ddf38e - std::thread::{{impl}}::spawn::{{closure}}<closure,()>
                               at C:\Users\matth\Code\Rust\rust\src\libstd\thread\mod.rs:393
  90:     0x7ff9a4ee49d9 - alloc::boxed::{{impl}}::call_box<(),closure>
                               at C:\Users\matth\Code\Rust\rust\src\liballoc\boxed.rs:682
  91:     0x7ff9a5dc3d6f - alloc::boxed::{{impl}}::call_once<(),()>
                               at C:\Users\matth\Code\Rust\rust\src\liballoc\boxed.rs:692
  92:     0x7ff9a5e6e6ef - std::sys_common::thread::start_thread
                               at C:\Users\matth\Code\Rust\rust\src\libstd\sys_common\thread.rs:21
  93:     0x7ff9a5e9592e - std::sys::imp::thread::{{impl}}::new::thread_start
                               at C:\Users\matth\Code\Rust\rust\src\libstd\sys\windows\thread.rs:51
  94:     0x7ff9ff7e2773 - BaseThreadInitThunk

[tirr-c]

If I add a trait bound T: X to the latter impl so that A<T> implements Z, the compiler give me a proper error message:

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

trait X {} 
trait Y: X {} 
trait Z { type Assoc: Y; }

struct A<T>(T);

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

error[E0210]: type parameter `T` must be used as the type parameter for some local type (e.g. `MyStruct<T>`); only traits defined in the current crate can be implemented for a type parameter
  --> src/lib.rs:11:1
   |
11 | impl<T: X> From<<A<T> as Z>::Assoc> for T {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[Alexendoo]

Same ICE as #43037