ICE with GAT and TAIT: cannot relate region: LUB(ReEarlyBound(0, 'a), ReErased)

[yshui]

Code

pub trait Trait {
    type Fut<'a> where Self: 'a;
    fn fun<'a, 'b>(&'a self, x: &'_ mut &'b ()) -> Self::Fut<'a>
    where
        'b: 'a;
}
impl Trait for () {
    type Fut<'a> = impl ::std::future::Future + 'a
    where
        Self: 'a;
    fn fun<'a, 'b>(&'a self, x: &'_ mut &'b ()) -> Self::Fut<'a>
    where
        'b: 'a,
    {
        async { }
    }
}

Meta

---

Regression in 2287107 (#98559)

---

searched nightlies: from nightly-2022-09-09 to nightly-2022-09-15
regressed nightly: nightly-2022-09-11
searched commit range: 1d37ed6...2287107
regressed commit: 2287107

bisected with cargo-bisect-rustc v0.6.4

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc ice --prompt

Backtrace

error: internal compiler error: compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs:536:17: cannot relate region: LUB(ReEarlyBound(0, 'a), ReErased)

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/compiler/rustc_errors/src/lib.rs:1458:9
stack backtrace:
   0:     0x7f5e49799c20 - std::backtrace_rs::backtrace::libunwind::trace::hf9cd4c385c25a2fe
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   1:     0x7f5e49799c20 - std::backtrace_rs::backtrace::trace_unsynchronized::hf9a1be2df46de98c
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f5e49799c20 - std::sys_common::backtrace::_print_fmt::ha770a6c3890b3cde
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/std/src/sys_common/backtrace.rs:66:5
   3:     0x7f5e49799c20 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h7099a61d18d47f5f
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/std/src/sys_common/backtrace.rs:45:22
   4:     0x7f5e497f4aee - core::fmt::write::h34c269a5556240be
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/core/src/fmt/mod.rs:1202:17
   5:     0x7f5e4978a835 - std::io::Write::write_fmt::h9b1d898decaac979
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/std/src/io/mod.rs:1679:15
   6:     0x7f5e4979c8d3 - std::sys_common::backtrace::_print::hb8325cbd910e0a42
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/std/src/sys_common/backtrace.rs:48:5
   7:     0x7f5e4979c8d3 - std::sys_common::backtrace::print::h52eaf8f4259fb854
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/std/src/sys_common/backtrace.rs:35:9
   8:     0x7f5e4979c8d3 - std::panicking::default_hook::{{closure}}::h38a1bd1ceb333281
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/std/src/panicking.rs:295:22
   9:     0x7f5e4979c5bf - std::panicking::default_hook::hbfa37b6c2aa83708
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/std/src/panicking.rs:314:9
  10:     0x7f5e4c003001 - <rustc_driver[f7b5b01335fbd434]::DEFAULT_HOOK::{closure#0}::{closure#0} as core[f6f8d9be6066ab2c]::ops::function::FnOnce<(&core[f6f8d9be6066ab2c]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  11:     0x7f5e4979d10d - std::panicking::rust_panic_with_hook::h6bfc21eea1a19790
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/std/src/panicking.rs:702:17
  12:     0x7f5e4d02b081 - std[81ab5d9a96a0142e]::panicking::begin_panic::<rustc_errors[e78c9e9af74db21c]::ExplicitBug>::{closure#0}
  13:     0x7f5e4d02a296 - std[81ab5d9a96a0142e]::sys_common::backtrace::__rust_end_short_backtrace::<std[81ab5d9a96a0142e]::panicking::begin_panic<rustc_errors[e78c9e9af74db21c]::ExplicitBug>::{closure#0}, !>
  14:     0x7f5e4cfb1a06 - std[81ab5d9a96a0142e]::panicking::begin_panic::<rustc_errors[e78c9e9af74db21c]::ExplicitBug>
  15:     0x7f5e4d028976 - std[81ab5d9a96a0142e]::panic::panic_any::<rustc_errors[e78c9e9af74db21c]::ExplicitBug>
  16:     0x7f5e4d025c0d - <rustc_errors[e78c9e9af74db21c]::HandlerInner>::bug::<&alloc[9d62437589f31483]::string::String>
  17:     0x7f5e4d0254c0 - <rustc_errors[e78c9e9af74db21c]::Handler>::bug::<&alloc[9d62437589f31483]::string::String>
  18:     0x7f5e4d0a5d3d - rustc_middle[af3205fb0fe14459]::ty::context::tls::with_context_opt::<rustc_middle[af3205fb0fe14459]::ty::context::tls::with_opt<rustc_middle[af3205fb0fe14459]::util::bug::opt_span_bug_fmt<rustc_span[352514dd70ceaa1d]::span_encoding::Span>::{closure#0}, ()>::{closure#0}, ()>
  19:     0x7f5e4d0a6a36 - rustc_middle[af3205fb0fe14459]::util::bug::opt_span_bug_fmt::<rustc_span[352514dd70ceaa1d]::span_encoding::Span>
  20:     0x7f5e4aa61fb3 - rustc_middle[af3205fb0fe14459]::util::bug::bug_fmt
  21:     0x7f5e4ab19997 - <rustc_infer[29b444941ee7ee25]::infer::lexical_region_resolve::LexicalResolver>::lub_concrete_regions
  22:     0x7f5e4ab1694b - rustc_infer[29b444941ee7ee25]::infer::lexical_region_resolve::resolve
  23:     0x7f5e4b4be94b - <rustc_infer[29b444941ee7ee25]::infer::InferCtxt>::resolve_regions_and_report_errors
  24:     0x7f5e4b4a7e6a - <rustc_infer[29b444941ee7ee25]::infer::InferCtxt>::check_region_obligations_and_report_errors
  25:     0x7f5e4b9580b5 - <rustc_infer[29b444941ee7ee25]::infer::InferCtxtBuilder>::enter::<(), rustc_typeck[a12c0d1dcfa26d23]::check::check::check_opaque_meets_bounds::{closure#0}>
  26:     0x7f5e4b931987 - rustc_typeck[a12c0d1dcfa26d23]::check::check::check_item_type
  27:     0x7f5e4b92e47e - rustc_typeck[a12c0d1dcfa26d23]::check::check::check_mod_item_types
  28:     0x7f5e4b129771 - <rustc_query_system[d9fae65d8b1eb5ad]::dep_graph::graph::DepGraph<rustc_middle[af3205fb0fe14459]::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle[af3205fb0fe14459]::ty::context::TyCtxt, rustc_span[352514dd70ceaa1d]::def_id::LocalDefId, ()>
  29:     0x7f5e4b1281f7 - rustc_query_system[d9fae65d8b1eb5ad]::query::plumbing::try_execute_query::<rustc_query_impl[1a54d4e1bcc8b675]::plumbing::QueryCtxt, rustc_query_system[d9fae65d8b1eb5ad]::query::caches::DefaultCache<rustc_span[352514dd70ceaa1d]::def_id::LocalDefId, ()>>
  30:     0x7f5e4ba7e039 - rustc_query_system[d9fae65d8b1eb5ad]::query::plumbing::get_query::<rustc_query_impl[1a54d4e1bcc8b675]::queries::check_mod_item_types, rustc_query_impl[1a54d4e1bcc8b675]::plumbing::QueryCtxt>
  31:     0x7f5e4bd1a50c - <rustc_middle[af3205fb0fe14459]::hir::map::Map>::for_each_module::<rustc_typeck[a12c0d1dcfa26d23]::check_crate::{closure#6}::{closure#0}>
  32:     0x7f5e4b314435 - rustc_typeck[a12c0d1dcfa26d23]::check_crate
  33:     0x7f5e4b313a27 - rustc_interface[5bcac5cfb78c3b1a]::passes::analysis
  34:     0x7f5e4bdcd852 - <rustc_query_system[d9fae65d8b1eb5ad]::dep_graph::graph::DepGraph<rustc_middle[af3205fb0fe14459]::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle[af3205fb0fe14459]::ty::context::TyCtxt, (), core[f6f8d9be6066ab2c]::result::Result<(), rustc_errors[e78c9e9af74db21c]::ErrorGuaranteed>>
  35:     0x7f5e4bdccf1a - rustc_query_system[d9fae65d8b1eb5ad]::query::plumbing::try_execute_query::<rustc_query_impl[1a54d4e1bcc8b675]::plumbing::QueryCtxt, rustc_query_system[d9fae65d8b1eb5ad]::query::caches::DefaultCache<(), core[f6f8d9be6066ab2c]::result::Result<(), rustc_errors[e78c9e9af74db21c]::ErrorGuaranteed>>>
  36:     0x7f5e4bdcc9e7 - rustc_query_system[d9fae65d8b1eb5ad]::query::plumbing::get_query::<rustc_query_impl[1a54d4e1bcc8b675]::queries::analysis, rustc_query_impl[1a54d4e1bcc8b675]::plumbing::QueryCtxt>
  37:     0x7f5e4adfaeb7 - <rustc_interface[5bcac5cfb78c3b1a]::passes::QueryContext>::enter::<rustc_driver[f7b5b01335fbd434]::run_compiler::{closure#1}::{closure#2}::{closure#3}, core[f6f8d9be6066ab2c]::result::Result<(), rustc_errors[e78c9e9af74db21c]::ErrorGuaranteed>>
  38:     0x7f5e4adee8cc - rustc_interface[5bcac5cfb78c3b1a]::interface::create_compiler_and_run::<core[f6f8d9be6066ab2c]::result::Result<(), rustc_errors[e78c9e9af74db21c]::ErrorGuaranteed>, rustc_driver[f7b5b01335fbd434]::run_compiler::{closure#1}>
  39:     0x7f5e4aded211 - <scoped_tls[de48490ce358b7ec]::ScopedKey<rustc_span[352514dd70ceaa1d]::SessionGlobals>>::set::<rustc_interface[5bcac5cfb78c3b1a]::interface::run_compiler<core[f6f8d9be6066ab2c]::result::Result<(), rustc_errors[e78c9e9af74db21c]::ErrorGuaranteed>, rustc_driver[f7b5b01335fbd434]::run_compiler::{closure#1}>::{closure#0}, core[f6f8d9be6066ab2c]::result::Result<(), rustc_errors[e78c9e9af74db21c]::ErrorGuaranteed>>
  40:     0x7f5e4adeceff - std[81ab5d9a96a0142e]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[5bcac5cfb78c3b1a]::util::run_in_thread_pool_with_globals<rustc_interface[5bcac5cfb78c3b1a]::interface::run_compiler<core[f6f8d9be6066ab2c]::result::Result<(), rustc_errors[e78c9e9af74db21c]::ErrorGuaranteed>, rustc_driver[f7b5b01335fbd434]::run_compiler::{closure#1}>::{closure#0}, core[f6f8d9be6066ab2c]::result::Result<(), rustc_errors[e78c9e9af74db21c]::ErrorGuaranteed>>::{closure#0}, core[f6f8d9be6066ab2c]::result::Result<(), rustc_errors[e78c9e9af74db21c]::ErrorGuaranteed>>
  41:     0x7f5e4be67000 - <<std[81ab5d9a96a0142e]::thread::Builder>::spawn_unchecked_<rustc_interface[5bcac5cfb78c3b1a]::util::run_in_thread_pool_with_globals<rustc_interface[5bcac5cfb78c3b1a]::interface::run_compiler<core[f6f8d9be6066ab2c]::result::Result<(), rustc_errors[e78c9e9af74db21c]::ErrorGuaranteed>, rustc_driver[f7b5b01335fbd434]::run_compiler::{closure#1}>::{closure#0}, core[f6f8d9be6066ab2c]::result::Result<(), rustc_errors[e78c9e9af74db21c]::ErrorGuaranteed>>::{closure#0}, core[f6f8d9be6066ab2c]::result::Result<(), rustc_errors[e78c9e9af74db21c]::ErrorGuaranteed>>::{closure#1} as core[f6f8d9be6066ab2c]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  42:     0x7f5e497a6ee3 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h2695b43ebae659e4
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/alloc/src/boxed.rs:1940:9
  43:     0x7f5e497a6ee3 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hf3b49b955267341c
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/alloc/src/boxed.rs:1940:9
  44:     0x7f5e497a6ee3 - std::sys::unix::thread::Thread::new::thread_start::h2bad5ab8a769c6c8
                               at /rustc/750bd1a7ff3e010611b97ee75d30b7cbf5f3a03c/library/std/src/sys/unix/thread.rs:108:17
  45:     0x7f5e494f46a3 - <unknown>
  46:     0x7f5e4957a52c - <unknown>
  47:                0x0 - <unknown>

[yshui]

Before the ICE regression, the error message was.. pretty weird:

error[E0478]: lifetime bound not satisfied
 --> src/lib.rs:9:20
  |
9 |     type Fut<'a> = impl ::std::future::Future + 'a
  |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: lifetime parameter instantiated with the empty lifetime
note: but lifetime parameter must outlive the lifetime `'a` as defined here
 --> src/lib.rs:9:14
  |
9 |     type Fut<'a> = impl ::std::future::Future + 'a
  |              ^^

For more information about this error, try `rustc --explain E0478`.

[yshui]

Ok, I think this is duplicate of #100267