rustc 1.59.0-nightly (c5ecc1570 2021-12-15): panic when trait bound not satisfied

[Chris00]

Code

The following code:

#[derive(Clone)]
struct P<T> {
    x: T,
    y: f64,
}

impl<T> P<T> {
    fn y(&self, y: f64) -> Self { P{y, .. self.clone() } }
}

triggers a panic in the compiler (see below). All works as expected if I write impl<T: Clone>.

Meta

rustc --version --verbose:

rustc 1.59.0-nightly (c5ecc1570 2021-12-15)
binary: rustc
commit-hash: c5ecc157043ba413568b09292001a4a74b541a4e
commit-date: 2021-12-15
host: x86_64-unknown-linux-gnu
release: 1.59.0-nightly
LLVM version: 13.0.0

Error output

   Compiling p1 v0.1.0 (/tmp/p1)
error[E0601]: `main` function not found in crate `pbm`
  --> src/pbm.rs:2:1
   |
2  | / #[derive(Clone)]
3  | | struct P<T> {
4  | |     x: T,
5  | |     y: f64,
...  |
9  | |     fn y(&self, y: f64) -> Self { P{y, .. self.clone() } }
10 | | }
   | |_^ consider adding a `main` function to `src/pbm.rs`

error: internal compiler error: compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs:321:26: while adjusting Expr { hir_id: HirId { owner: DefId(0:5 ~ pbm[38a7]::{impl#0}::y), local_id: 7 }, kind: Path(Resolved(None, Path { span: src/pbm.rs:9:43: 9:47 (#0), res: Local(HirId { owner: DefId(0:5 ~ pbm[38a7]::{impl#0}::y), local_id: 2 }), segments: [PathSegment { ident: self#0, hir_id: Some(HirId { owner: DefId(0:5 ~ pbm[38a7]::{impl#0}::y), local_id: 6 }), res: Some(Local(HirId { owner: DefId(0:5 ~ pbm[38a7]::{impl#0}::y), local_id: 2 })), args: None, infer_args: true }] })), span: src/pbm.rs:9:43: 9:47 (#0) }, can't compose [Borrow(Ref('_#0r, Not)) -> &&P<T>] and [Borrow(Ref('_#4r, Not)) -> &&P<T>]

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1169:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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 1.59.0-nightly (c5ecc1570 2021-12-15) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental -C target-cpu=haswell --crate-type bin

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [typeck] type-checking `<impl at src/pbm.rs:8:1: 10:2>::y`
#1 [typeck_item_bodies] type-checking all item bodies
end of query stack
For more information about this error, try `rustc --explain E0601`.
error: could not compile `p1` due to previous error

rust-compilation exited abnormally with code 101 at Fri Dec 17 00:25:13

Backtrace

RUST_BACKTRACE=1 cargo build
   Compiling p1 v0.1.0 (/tmp/p1)
error[E0601]: `main` function not found in crate `pbm`
  --> src/pbm.rs:2:1
   |
2  | / #[derive(Clone)]
3  | | struct P<T> {
4  | |     x: T,
5  | |     y: f64,
...  |
9  | |     fn y(&self, y: f64) -> Self { P{y, .. self.clone() } }
10 | | }
   | |_^ consider adding a `main` function to `src/pbm.rs`

error: internal compiler error: compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs:321:26: while adjusting Expr { hir_id: HirId { owner: DefId(0:5 ~ pbm[38a7]::{impl#0}::y), local_id: 7 }, kind: Path(Resolved(None, Path { span: src/pbm.rs:9:43: 9:47 (#0), res: Local(HirId { owner: DefId(0:5 ~ pbm[38a7]::{impl#0}::y), local_id: 2 }), segments: [PathSegment { ident: self#0, hir_id: Some(HirId { owner: DefId(0:5 ~ pbm[38a7]::{impl#0}::y), local_id: 6 }), res: Some(Local(HirId { owner: DefId(0:5 ~ pbm[38a7]::{impl#0}::y), local_id: 2 })), args: None, infer_args: true }] })), span: src/pbm.rs:9:43: 9:47 (#0) }, can't compose [Borrow(Ref('_#0r, Not)) -> &&P<T>] and [Borrow(Ref('_#4r, Not)) -> &&P<T>]

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1169:9
stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: std::panic::panic_any::<rustc_errors::ExplicitBug>
   2: <rustc_errors::HandlerInner>::bug
   3: <rustc_errors::Handler>::bug
   4: rustc_middle::ty::context::tls::with_opt::<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, ()>
   5: rustc_middle::util::bug::opt_span_bug_fmt::<rustc_span::span_encoding::Span>
   6: rustc_middle::util::bug::bug_fmt
   7: <rustc_typeck::check::fn_ctxt::FnCtxt>::apply_adjustments
   8: <rustc_typeck::check::method::confirm::ConfirmContext>::confirm
   9: <rustc_typeck::check::fn_ctxt::FnCtxt>::lookup_method
  10: <rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_kind
  11: <rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  12: <rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_kind
  13: <rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  14: <rustc_typeck::check::fn_ctxt::FnCtxt>::check_block_with_expected
  15: <rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  16: rustc_typeck::check::check::check_fn
  17: <rustc_infer::infer::InferCtxtBuilder>::enter::<&rustc_middle::ty::context::TypeckResults, <rustc_typeck::check::inherited::InheritedBuilder>::enter<rustc_typeck::check::typeck_with_fallback<rustc_typeck::check::typeck::{closure#0}>::{closure#1}, &rustc_middle::ty::context::TypeckResults>::{closure#0}>
  18: rustc_typeck::check::typeck
  19: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::ty::context::TypeckResults>
  20: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_middle::ty::context::TypeckResults, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::ty::context::TypeckResults>::{closure#3}>
  21: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalDefId, &rustc_middle::ty::context::TypeckResults>>
  22: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::typeck
  23: <rustc_middle::hir::map::Map>::par_body_owners::<rustc_typeck::check::typeck_item_bodies::{closure#0}>
  24: rustc_typeck::check::typeck_item_bodies
  25: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, (), ()>
  26: rustc_data_structures::stack::ensure_sufficient_stack::<((), rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, (), ()>::{closure#3}>
  27: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<(), ()>>
  28: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::typeck_item_bodies, rustc_query_impl::plumbing::QueryCtxt>
  29: <rustc_session::session::Session>::time::<(), rustc_typeck::check_crate::{closure#7}>
  30: rustc_typeck::check_crate
  31: rustc_interface::passes::analysis
  32: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, (), core::result::Result<(), rustc_errors::ErrorReported>>
  33: rustc_data_structures::stack::ensure_sufficient_stack::<(core::result::Result<(), rustc_errors::ErrorReported>, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, (), core::result::Result<(), rustc_errors::ErrorReported>>::{closure#3}>
  34: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<(), core::result::Result<(), rustc_errors::ErrorReported>>>
  35: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::analysis, rustc_query_impl::plumbing::QueryCtxt>
  36: <rustc_interface::passes::QueryContext>::enter::<rustc_driver::run_compiler::{closure#1}::{closure#2}::{closure#3}, core::result::Result<(), rustc_errors::ErrorReported>>
  37: <rustc_interface::interface::Compiler>::enter::<rustc_driver::run_compiler::{closure#1}::{closure#2}, core::result::Result<core::option::Option<rustc_interface::queries::Linker>, rustc_errors::ErrorReported>>
  38: rustc_span::with_source_map::<core::result::Result<(), rustc_errors::ErrorReported>, rustc_interface::interface::create_compiler_and_run<core::result::Result<(), rustc_errors::ErrorReported>, rustc_driver::run_compiler::{closure#1}>::{closure#1}>
  39: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorReported>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorReported>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_errors::ErrorReported>>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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 1.59.0-nightly (c5ecc1570 2021-12-15) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental -C target-cpu=haswell --crate-type bin

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [typeck] type-checking `<impl at src/pbm.rs:8:1: 10:2>::y`
#1 [typeck_item_bodies] type-checking all item bodies
#2 [analysis] running analysis passes on this crate
end of query stack
For more information about this error, try `rustc --explain E0601`.
error: could not compile `p1` due to previous error

Compilation exited abnormally with code 101 at Fri Dec 17 00:26:54

[SNCPlay42]

Output on stable:

error[E0308]: mismatched types
 --> <source>:8:43
  |
8 |     fn y(&self, y: f64) -> Self { P{y, .. self.clone() } }
  |                                           ^^^^^^^^^^^^ expected struct `P`, found `&P<T>`
  |
  = note: expected struct `P<T>`
          found reference `&P<T>`

(An awkward but correct error - without T: Clone, the compiler uses autoref to resolve clone as <&T as Clone>::clone which returns &T.)

---

searched nightlies: from nightly-2021-10-16 to nightly-2021-11-28
regressed nightly: nightly-2021-11-10
searched commit range: 495322d...8b09ba6
regressed commit: 8b09ba6

bisected with cargo-bisect-rustc v0.6.1

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

cargo bisect-rustc --preserve --start=2021-10-16 --end=2021-11-28 --regress=ice 

@rustbot label regression-from-stable-to-beta

[nbdd0121]

Probably #90035?

[apiraino]

Assigning priority as discussed in the Zulip thread of the Prioritization Working Group.

@rustbot label -I-prioritize +P-medium

[compiler-errors]

I think this is a duplicate of #91502, and I also put up a fix in #91538 (along with both @SparrowLii in #92112 and @Aaron1011 in #92083) which has been waiting for a review for quite some time..

Not sure which one of our PRs should be approved, but at least one of them should :^) -- re: #92112, I agree with Aaron that this is the simpler and more targeted fix for the bug, so I'll just close mine after this gets approved probably.

(edit: made it clearer who I was referring to in the original comment - lol, sorry)

[apiraino]

thanks @compiler-errors for the note! I'll also add (as a self-reminder) that in #92083 Aaron also mentions that #92112 might be a better fix.