check for inference var leaks before rollback

[lcnr]

When rolling back a snapshot, we must be careful to not leak any inference vars created in that snapshot. This PR implements an even stronger check by not allowing any inference vars during rollback.

Inspired by #100473 (comment), I think this is worth the additional, otherwise pretty useless, TypeVisitable impls.

r? @rust-lang/types

[lcnr]

xd, should change my config.toml to actually enable debug assertions 😁

[rust-log-analyzer]

The job x86_64-gnu-llvm-13 failed! Check out the build log: (web)(plain)

Click to see the possible cause of the failure (guessed by this bot)

 Compiling memchr v2.5.0
Compiling std v0.0.0 (/checkout/library/std)
Compiling compiler_builtins v0.1.79
Compiling unwind v0.0.0 (/checkout/library/unwind)
thread 'rustc' panicked at 'commit_if_ok: leaking infer vars: Sorts(ExpectedFound { expected: ops::try_trait::NeverShortCircuit<_>, found: impl FnMut(A, B) -> T })', /checkout/compiler/rustc_infer/src/infer/mod.rs:857:17
0: 0x7ff683c144dd - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h4e6b7fb551e71cc8
0: 0x7ff683c144dd - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h4e6b7fb551e71cc8
1: 0x7ff683c7a088 - core::fmt::write::hf362fe59869d8c74
2: 0x7ff683c05971 - std::io::Write::write_fmt::ha85333391a02ae5e
3: 0x7ff683c174ee - std::panicking::default_hook::{{closure}}::h366a70b549eb81be
4: 0x7ff683c171b7 - std::panicking::default_hook::ha6465a1ed0618f24
5: 0x7ff68458b5a4 - rustc_driver[ed0aca8193ad4d2a]::DEFAULT_HOOK::{closure#0}::{closure#0}
6: 0x7ff683c17c91 - std::panicking::rust_panic_with_hook::h8f6ccc3b7223595a
7: 0x7ff683c17ab7 - std::panicking::begin_panic_handler::{{closure}}::h18568d4e1d0476f8
8: 0x7ff683c14a84 - std::sys_common::backtrace::__rust_end_short_backtrace::h1552466bfc796a40
9: 0x7ff683c17792 - rust_begin_unwind
10: 0x7ff683bcab33 - core::panicking::panic_fmt::h6e05302598fc1908
11: 0x7ff686ad3c88 - <rustc_infer[bb1e8f5dae528630]::infer::InferCtxt>::commit_if_ok::<rustc_infer[bb1e8f5dae528630]::infer::InferOk<()>, rustc_middle[5cd9fb4390de6444]::ty::error::TypeError, <rustc_infer[bb1e8f5dae528630]::infer::at::Trace>::sub<rustc_middle[5cd9fb4390de6444]::ty::sty::Binder<rustc_middle[5cd9fb4390de6444]::ty::sty::TraitRef>>::{closure#0}>
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14: 0x7ff686b233fd - <rustc_trait_selection[844becf19fb2305a]::traits::select::SelectionContext>::match_where_clause_trait_ref
15: 0x7ff686ada783 - <rustc_infer[bb1e8f5dae528630]::infer::InferCtxt>::probe::<core[2435b9faef444c77]::result::Result<rustc_middle[5cd9fb4390de6444]::traits::select::EvaluationResult, rustc_middle[5cd9fb4390de6444]::traits::select::OverflowError>, <rustc_trait_selection[844becf19fb2305a]::traits::select::SelectionContext>::evaluation_probe<<rustc_trait_selection[844becf19fb2305a]::traits::select::SelectionContext>::where_clause_may_apply::{closure#0}>::{closure#0}>
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20: 0x7ff686b2045d - <rustc_trait_selection[844becf19fb2305a]::traits::select::SelectionContext>::select_from_obligation
21: 0x7ff686b38b57 - <rustc_trait_selection[844becf19fb2305a]::traits::select::SelectionContext>::select
22: 0x7ff686c1cb69 - <rustc_trait_selection[844becf19fb2305a]::traits::fulfill::FulfillProcessor>::process_trait_obligation
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27: 0x7ff684e5daaa - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::structurally_resolved_type
28: 0x7ff684e37b54 - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_call
29: 0x7ff684ea7e34 - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_expr_kind
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31: 0x7ff684ea6d49 - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_expr_with_expectation
32: 0x7ff684e4f5cc - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_return_expr
33: 0x7ff68512846f - rustc_typeck[8362f351ad18833d]::check::check::check_fn
34: 0x7ff684e9f820 - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_expr_closure
35: 0x7ff684ea75bd - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_expr_kind
36: 0x7ff684e4dbdd - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
37: 0x7ff684ea6d49 - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_expr_with_expectation
38: 0x7ff684e676a6 - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_block_with_expected
39: 0x7ff684ea81ec - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_expr_kind
40: 0x7ff684e4dbdd - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
41: 0x7ff684ea6d49 - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_expr_with_expectation
42: 0x7ff684e4f5cc - <rustc_typeck[8362f351ad18833d]::check::fn_ctxt::FnCtxt>::check_return_expr
43: 0x7ff68512846f - rustc_typeck[8362f351ad18833d]::check::check::check_fn
44: 0x7ff68503c9b1 - <rustc_infer[bb1e8f5dae528630]::infer::InferCtxtBuilder>::enter::<&rustc_middle[5cd9fb4390de6444]::ty::context::TypeckResults, <rustc_typeck[8362f351ad18833d]::check::inherited::InheritedBuilder>::enter<rustc_typeck[8362f351ad18833d]::check::typeck_with_fallback<rustc_typeck[8362f351ad18833d]::check::typeck::{closure#0}>::{closure#1}, &rustc_middle[5cd9fb4390de6444]::ty::context::TypeckResults>::{closure#0}>
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51: 0x7ff685503e1d - rustc_mir_build[a61a09dc8858d1a5]::build::mir_built
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53: 0x7ff686213d46 - rustc_query_system[ef2ce6c958997f32]::query::plumbing::get_query::<rustc_query_impl[8be34b0be0a94569]::queries::mir_built, rustc_query_impl[8be34b0be0a94569]::plumbing::QueryCtxt>
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55: 0x7ff684bd0738 - rustc_mir_transform[ea9ef29f418067c]::check_unsafety::unsafety_check_result
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68: 0x7ff6857d7aee - <rustc_borrowck[e1608fedcc7d9ab1]::provide::{closure#0} as core[2435b9faef444c77]::ops::function::FnOnce<(rustc_middle[5cd9fb4390de6444]::ty::context::TyCtxt, rustc_span[b0612a3315eed503]::def_id::LocalDefId)>>::call_once
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100: 0x7ff6845e4cf5 - <rustc_interface[1b0e5f28d4a6f587]::passes::QueryContext>::enter::<rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}::{closure#2}::{closure#3}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>
101: 0x7ff6845929e8 - <rustc_interface[1b0e5f28d4a6f587]::interface::Compiler>::enter::<rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}::{closure#2}, core[2435b9faef444c77]::result::Result<core[2435b9faef444c77]::option::Option<rustc_interface[1b0e5f28d4a6f587]::queries::Linker>, rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>
102: 0x7ff684577a29 - rustc_span[b0612a3315eed503]::with_source_map::<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_interface[1b0e5f28d4a6f587]::interface::create_compiler_and_run<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}>::{closure#1}>
103: 0x7ff684593dae - rustc_interface[1b0e5f28d4a6f587]::interface::create_compiler_and_run::<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}>
104: 0x7ff68456f652 - <scoped_tls[7d6eb79a6adf8b31]::ScopedKey<rustc_span[b0612a3315eed503]::SessionGlobals>>::set::<rustc_interface[1b0e5f28d4a6f587]::interface::run_compiler<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>
105: 0x7ff68457b7d9 - std[1cd9e72d2caaad51]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[1b0e5f28d4a6f587]::util::run_in_thread_pool_with_globals<rustc_interface[1b0e5f28d4a6f587]::interface::run_compiler<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>
106: 0x7ff6845f0e0e - std[1cd9e72d2caaad51]::panicking::try::<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, core[2435b9faef444c77]::panic::unwind_safe::AssertUnwindSafe<<std[1cd9e72d2caaad51]::thread::Builder>::spawn_unchecked_<rustc_interface[1b0e5f28d4a6f587]::util::run_in_thread_pool_with_globals<rustc_interface[1b0e5f28d4a6f587]::interface::run_compiler<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>::{closure#1}::{closure#0}>>
107: 0x7ff6845ec6e0 - <<std[1cd9e72d2caaad51]::thread::Builder>::spawn_unchecked_<rustc_interface[1b0e5f28d4a6f587]::util::run_in_thread_pool_with_globals<rustc_interface[1b0e5f28d4a6f587]::interface::run_compiler<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>::{closure#1} as core[2435b9faef444c77]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
108: 0x7ff683c23a95 - std::sys::unix::thread::Thread::new::thread_start::he0a2b2e0966bd38e
109: 0x7ff6839c3b43 - <unknown>
110: 0x7ff683a55a00 - <unknown>
111: 0x0 - <unknown>
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/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md
note: rustc 1.65.0-nightly (36998d755 2022-08-19) running on x86_64-unknown-linux-gnu
note: compiler flags: --crate-type lib -C opt-level=3 -C embed-bitcode=no -C codegen-units=1 -C debuginfo=0 -C debug-assertions=on -Z unstable-options -C symbol-mangling-version=legacy -Z unstable-options -Z unstable-options -Z macro-backtrace -C link-args=-Wl,-z,origin -C link-args=-Wl,-rpath,$ORIGIN/../lib -Z unstable-options -C split-debuginfo=off -C prefer-dynamic -C llvm-args=-import-instr-limit=10 -C embed-bitcode=yes -Z crate-attr=doc(html_root_url="https://doc.rust-lang.org/nightly/") -Z binary-dep-depinfo -Z force-unstable-if-unmarked
note: some of the compiler flags provided by cargo are hidden
query stack during panic:
query stack during panic:
#0 [typeck] type-checking `ops::try_trait::<impl at library/core/src/ops/try_trait.rs:378:1: 378:29>::wrap_mut_2`
#1 [mir_built] building MIR for `ops::try_trait::<impl at library/core/src/ops/try_trait.rs:378:1: 378:29>::wrap_mut_2`
#2 [unsafety_check_result] unsafety-checking `ops::try_trait::<impl at library/core/src/ops/try_trait.rs:378:1: 378:29>::wrap_mut_2`
#3 [mir_const] processing MIR for `ops::try_trait::<impl at library/core/src/ops/try_trait.rs:378:1: 378:29>::wrap_mut_2`
#4 [mir_promoted] processing `ops::try_trait::<impl at library/core/src/ops/try_trait.rs:378:1: 378:29>::wrap_mut_2`
#5 [mir_borrowck] borrow-checking `ops::try_trait::<impl at library/core/src/ops/try_trait.rs:378:1: 378:29>::wrap_mut_2`
#6 [type_of] computing type of `ops::try_trait::<impl at library/core/src/ops/try_trait.rs:378:1: 378:29>::wrap_mut_2::{opaque#1}`
#7 [privacy_access_levels] privacy access levels
#8 [analysis] running analysis passes on this crate
end of query stack
error: internal compiler error: no errors encountered even though `delay_span_bug` issued
error: internal compiler error: VecMap([(OpaqueTypeKey { def_id: DefId(0:3756 ~ core[8b5e]::ops::try_trait::{impl#0}::wrap_mut_2::{opaque#1}), substs: [T, A, B, impl FnMut(A, B) -> T] }, OpaqueTypeDecl { hidden_type: OpaqueHiddenType { span: library/core/src/ops/try_trait.rs:381:62: 381:86 (#21591), ty: _ }, origin: FnReturn(DefId(0:3752 ~ core[8b5e]::ops::try_trait::{impl#0}::wrap_mut_2)) })])
= note: delayed at compiler/rustc_infer/src/infer/opaque_types/table.rs:50:26
thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1427:13
stack backtrace:
stack backtrace:
0: 0x7ff683c144dd - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h4e6b7fb551e71cc8
1: 0x7ff683c7a088 - core::fmt::write::hf362fe59869d8c74
2: 0x7ff683c05971 - std::io::Write::write_fmt::ha85333391a02ae5e
3: 0x7ff683c174ee - std::panicking::default_hook::{{closure}}::h366a70b549eb81be
4: 0x7ff683c171b7 - std::panicking::default_hook::ha6465a1ed0618f24
5: 0x7ff68458b5a4 - rustc_driver[ed0aca8193ad4d2a]::DEFAULT_HOOK::{closure#0}::{closure#0}
6: 0x7ff683c17c91 - std::panicking::rust_panic_with_hook::h8f6ccc3b7223595a
7: 0x7ff68723a163 - std[1cd9e72d2caaad51]::panicking::begin_panic::<rustc_errors[50337c4cf14ec633]::ExplicitBug>::{closure#0}
8: 0x7ff687239eb6 - std[1cd9e72d2caaad51]::sys_common::backtrace::__rust_end_short_backtrace::<std[1cd9e72d2caaad51]::panicking::begin_panic<rustc_errors[50337c4cf14ec633]::ExplicitBug>::{closure#0}, !>
9: 0x7ff684549df6 - std[1cd9e72d2caaad51]::panicking::begin_panic::<rustc_errors[50337c4cf14ec633]::ExplicitBug>
10: 0x7ff68722e3f6 - std[1cd9e72d2caaad51]::panic::panic_any::<rustc_errors[50337c4cf14ec633]::ExplicitBug>
11: 0x7ff6872336b2 - <rustc_errors[50337c4cf14ec633]::HandlerInner as core[2435b9faef444c77]::ops::drop::Drop>::drop
12: 0x7ff6845a9c92 - core[2435b9faef444c77]::ptr::drop_in_place::<rustc_session[dc5821d9aef77b9e]::parse::ParseSess>
13: 0x7ff6845b1325 - <alloc[97a5c949eb0684ac]::rc::Rc<rustc_session[dc5821d9aef77b9e]::session::Session> as core[2435b9faef444c77]::ops::drop::Drop>::drop
14: 0x7ff68457a52c - core[2435b9faef444c77]::ptr::drop_in_place::<rustc_interface[1b0e5f28d4a6f587]::interface::Compiler>
15: 0x7ff684577e31 - rustc_span[b0612a3315eed503]::with_source_map::<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_interface[1b0e5f28d4a6f587]::interface::create_compiler_and_run<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}>::{closure#1}>
16: 0x7ff684593dae - rustc_interface[1b0e5f28d4a6f587]::interface::create_compiler_and_run::<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}>
17: 0x7ff68456f652 - <scoped_tls[7d6eb79a6adf8b31]::ScopedKey<rustc_span[b0612a3315eed503]::SessionGlobals>>::set::<rustc_interface[1b0e5f28d4a6f587]::interface::run_compiler<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>
18: 0x7ff68457b7d9 - std[1cd9e72d2caaad51]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[1b0e5f28d4a6f587]::util::run_in_thread_pool_with_globals<rustc_interface[1b0e5f28d4a6f587]::interface::run_compiler<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>
19: 0x7ff6845f0e0e - std[1cd9e72d2caaad51]::panicking::try::<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, core[2435b9faef444c77]::panic::unwind_safe::AssertUnwindSafe<<std[1cd9e72d2caaad51]::thread::Builder>::spawn_unchecked_<rustc_interface[1b0e5f28d4a6f587]::util::run_in_thread_pool_with_globals<rustc_interface[1b0e5f28d4a6f587]::interface::run_compiler<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>::{closure#1}::{closure#0}>>
20: 0x7ff6845ec6e0 - <<std[1cd9e72d2caaad51]::thread::Builder>::spawn_unchecked_<rustc_interface[1b0e5f28d4a6f587]::util::run_in_thread_pool_with_globals<rustc_interface[1b0e5f28d4a6f587]::interface::run_compiler<core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>, rustc_driver[ed0aca8193ad4d2a]::run_compiler::{closure#1}>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>::{closure#0}, core[2435b9faef444c77]::result::Result<(), rustc_errors[50337c4cf14ec633]::ErrorGuaranteed>>::{closure#1} as core[2435b9faef444c77]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
21: 0x7ff683c23a95 - std::sys::unix::thread::Thread::new::thread_start::he0a2b2e0966bd38e
22: 0x7ff6839c3b43 - <unknown>
23: 0x7ff683a55a00 - <unknown>
24: 0x0 - <unknown>
note: the compiler unexpectedly panicked. this is a bug.
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 1.65.0-nightly (36998d755 2022-08-19) running on x86_64-unknown-linux-gnu
note: compiler flags: --crate-type lib -C opt-level=3 -C embed-bitcode=no -C codegen-units=1 -C debuginfo=0 -C debug-assertions=on -Z unstable-options -C symbol-mangling-version=legacy -Z unstable-options -Z unstable-options -Z macro-backtrace -C link-args=-Wl,-z,origin -C link-args=-Wl,-rpath,$ORIGIN/../lib -Z unstable-options -C split-debuginfo=off -C prefer-dynamic -C llvm-args=-import-instr-limit=10 -C embed-bitcode=yes -Z crate-attr=doc(html_root_url="https://doc.rust-lang.org/nightly/") -Z binary-dep-depinfo -Z force-unstable-if-unmarked
note: some of the compiler flags provided by cargo are hidden
query stack during panic:
end of query stack
end of query stack
thread panicked while panicking. aborting.
rustc exited with signal: 6 (SIGABRT) (core dumped)
Caused by:
Caused by:
process didn't exit successfully: `/checkout/obj/build/bootstrap/debug/rustc --crate-name core --edition=2021 library/core/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C embed-bitcode=no -C codegen-units=1 -C debuginfo=0 -C debug-assertions=on -Zunstable-options --check-cfg 'names()' --check-cfg 'values()' -C metadata=fa992565d2130c71 -C extra-filename=-fa992565d2130c71 --out-dir /checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps --target x86_64-unknown-linux-gnu -L dependency=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps -L dependency=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/release/deps -Csymbol-mangling-version=legacy -Zunstable-options -Zunstable-options '--check-cfg=values(bootstrap)' '--check-cfg=values(stdarch_intel_sde)' '--check-cfg=values(no_fp_fmt_parse)' '--check-cfg=values(no_global_oom_handling)' '--check-cfg=values(freebsd12)' '--check-cfg=values(backtrace_in_libstd)' '--check-cfg=values(target_env,"libnx")' '--check-cfg=values(target_os,"watchos")' '--check-cfg=values(target_arch,"asmjs","spirv","nvptx","nvptx64","le32","xtensa")' '--check-cfg=values(dont_compile_me)' -Zmacro-backtrace -Clink-args=-Wl,-z,origin '-Clink-args=-Wl,-rpath,$ORIGIN/../lib' -Zunstable-options -Csplit-debuginfo=off -Cprefer-dynamic -Cllvm-args=-import-instr-limit=10 -Cembed-bitcode=yes '-Zcrate-attr=doc(html_root_url="https://doc.rust-lang.org/nightly/")' -Z binary-dep-depinfo` (exit status: 254)
Build completed unsuccessfully in 0:03:03

[compiler-errors]

Hehe what a coincidence that I get assigned this PR. I actually tried this with very similar motivation, but hit the same debug assertions as you're hitting and gave up. Curious to see if we can get this totally solved, though.

[bors]

☔ The latest upstream changes (presumably #101225) made this pull request unmergeable. Please resolve the merge conflicts.

[lcnr]

so afaict inference variables actually remain valid, we just drop any unifications from inside of the snapshot 🤔 so i guess while still weird, this isn't a soundness issue?

idk, still unhappy but don't know of an easy way to improve anything here