Compiler panics during incremental recompilation, while using an associated constant as array size

[vkorenev]

Code

use std::mem::size_of;

trait Tr {
    type Arr;

    const C: usize = size_of::<u64>();
}

impl Tr for str {
    type Arr = [u8; Self::C];
}

rustc --version --verbose

rustc 1.30.0-nightly (f2302da 2018-09-12)
binary: rustc
commit-hash: f2302da
commit-date: 2018-09-12
host: x86_64-unknown-linux-gnu
release: 1.30.0-nightly
LLVM version: 8.0

Stack trace

thread 'main' panicked at 'did not find a cycle', librustc/ty/query/job.rs:144:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:481
   6: std::panicking::begin_panic
   7: rustc::ty::query::job::QueryJob::await
   8: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
   9: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_const
  10: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  11: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  12: rustc::traits::project::opt_normalize_projection_type
  13: rustc::traits::project::normalize_projection_type
  14: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  15: <smallvec::SmallVec<A> as core::iter::traits::FromIterator<<A as smallvec::Array>::Item>>::from_iter
  16: rustc::ty::fold::TypeFoldable::fold_with
  17: rustc::ty::fold::TypeFoldable::fold_with
  18: rustc::ty::fold::TypeFoldable::fold_with
  19: rustc::traits::project::normalize
  20: rustc::infer::InferCtxt::partially_normalize_associated_types_in
  21: rustc_typeck::check::FnCtxt::instantiate_bounds
  22: rustc_typeck::check::FnCtxt::instantiate_value_path
  23: rustc_typeck::check::FnCtxt::check_expr_kind
  24: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_needs
  25: rustc::ty::context::tls::with_related_context
  26: rustc::infer::InferCtxtBuilder::enter
  27: rustc_typeck::check::typeck_tables_of
  28: rustc::ty::query::__query_compute::typeck_tables_of
  29: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::typeck_tables_of<'tcx>>::compute
  30: rustc::ty::context::tls::with_context
  31: rustc::dep_graph::graph::DepGraph::with_task_impl
  32: rustc::ty::context::tls::with_related_context
  33: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  34: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query
  35: rustc::ty::query::plumbing::force_from_dep_node
  36: rustc::dep_graph::graph::DepGraph::try_mark_green
  37: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_mark_green_and_read
  38: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  39: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_const
  40: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  41: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  42: rustc::traits::project::opt_normalize_projection_type
  43: rustc::traits::project::normalize_projection_type
  44: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  45: rustc::ty::fold::TypeFoldable::fold_with
  46: rustc::ty::fold::TypeFoldable::fold_with
  47: rustc::traits::project::normalize
  48: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &'a mut F>::call_once
  49: <core::iter::FlatMap<I, U, F> as core::iter::iterator::Iterator>::next
  50: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  51: rustc::ty::wf::WfPredicates::normalize
  52: rustc::ty::wf::trait_obligations
  53: rustc::ty::context::tls::with_related_context
  54: rustc::infer::InferCtxtBuilder::enter
  55: rustc_typeck::check::wfcheck::check_item_well_formed
  56: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::check_item_well_formed<'tcx>>::compute
  57: rustc::ty::context::tls::with_context
  58: rustc::dep_graph::graph::DepGraph::with_task_impl
  59: rustc::ty::context::tls::with_related_context
  60: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  61: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  62: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::ensure_query
  63: rustc::hir::Crate::visit_all_item_likes
  64: rustc::session::Session::track_errors
  65: rustc::util::common::time
  66: rustc_typeck::check_crate
  67: rustc::ty::context::tls::enter_context
  68: <std::thread::local::LocalKey<T>>::with
  69: rustc::ty::context::TyCtxt::create_and_enter
  70: rustc_driver::driver::compile_input
  71: rustc_driver::run_compiler_with_pool
  72: <scoped_tls::ScopedKey<T>>::set
  73: rustc_driver::run_compiler
  74: syntax::with_globals
  75: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:102
  76: rustc_driver::run
  77: rustc_driver::main
  78: std::rt::lang_start::{{closure}}
  79: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  80: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:102
  81: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:392
             at libstd/rt.rs:58
  82: main
  83: __libc_start_main
  84: <unknown>
query stack during panic:
#0 [typeck_tables_of] processing `<str as ice::Tr>::Arr::{{constant}}`
#1 [check_item_well_formed] processing `<str as ice::Tr>`
end of query stack

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 1.30.0-nightly (f2302daef 2018-09-12) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin

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

[memoryruins]

Do you experience an ICE on the latest nightly?

rustc 1.30.0-nightly (2ab3eba30 2018-09-14)

error[E0391]: cycle detected when const-evaluating `<impl at src/main.rs:9:1: 11:2>::Arr::{{constant}}`
  --> src/main.rs:10:21
   |
10 |     type Arr = [u8; Self::C];
   |                     ^^^^^^^
   |
note: ...which requires processing `<impl at src/main.rs:9:1: 11:2>::Arr::{{constant}}`...
  --> src/main.rs:10:21
   |
10 |     type Arr = [u8; Self::C];
   |                     ^^^^^^^
   = note: ...which again requires const-evaluating `<impl at src/main.rs:9:1: 11:2>::Arr::{{constant}}`, completing the cycle
note: cycle used when processing `<impl at src/main.rs:9:1: 11:2>`
  --> src/main.rs:9:1
   |
9  | impl Tr for str {
   | ^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0391`.

[vkorenev]

No longer occurs on rustc 1.30.0-nightly (2ab3eba30 2018-09-14).

[memoryruins]

@RalfJung do you think #54076 helped prevent the ICE? I could be overlooking another PR that might have helped. Either way, should this example be added to the test suite?

[RalfJung]

Uh, no idea. I would be rather surprised. But yeah it seems prudent to add this as a test-case.

Though, should this really be a cycle? C does not actually depend on Arr. Cc @eddyb @oli-obk

[memoryruins]

The same cycle detected error occurs on current stable as well.
rust version 1.29.0 (aa3ca1994 2018-09-11)

Edit: The same cycle error, with some minor tweaks to diagnostic wording, occurs on every stable version since 1.20. Associated constants were experimental in 1.19.

[eddyb]

I guess this should work, given that Self::C is <str as Tr>::C and so shouldn't fall under #43408.

cc @nikomatsakis

[memoryruins]

In hindsight, I should have done this originally. Tried 1.30.0-nightly (f2302daef 2018-09-12) from the original post on Linux and Windows, but I was unable to recreate the ICE. @vkorenev did you experience it in a new/clean project or pre-existing project?

[vkorenev]

I have found steps to reproduce it on the latest nightly (2224a42 2018-09-17):

1. Create a project with the following lib.rs

use std::mem::size_of;

trait Tr {
    type Arr;

    const C: usize = size_of::<u64>();

    fn get_arr() -> Self::Arr;
}

impl Tr for str {
    type Arr = [u8; 8];

    fn get_arr() -> Self::Arr {
        [0; Self::C]
    }
}

2. cargo clean
3. cargo build
4. Replace type Arr = [u8; 8]; with type Arr = [u8; Self::C];
5. cargo build results in

thread 'main' panicked at 'did not find a cycle', librustc/ty/query/job.rs:144:9                         
stack backtrace:                                                                                         
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace                                          
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49                                            
   1: std::sys_common::backtrace::print                                                                  
             at libstd/sys_common/backtrace.rs:71                                                        
             at libstd/sys_common/backtrace.rs:59                                                        
   2: std::panicking::default_hook::{{closure}}                                                          
             at libstd/panicking.rs:211                                                                  
   3: std::panicking::default_hook                                                                       
             at libstd/panicking.rs:227                                                                  
   4: rustc::util::common::panic_hook                                                                    
   5: std::panicking::rust_panic_with_hook                                                               
             at libstd/panicking.rs:481                                                                  
   6: std::panicking::begin_panic                                                                        
   7: rustc::ty::query::job::QueryJob::await                                                             
   8: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query           
   9: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_const
  10: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  11: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  12: rustc::traits::project::opt_normalize_projection_type                                              
  13: rustc::traits::project::normalize_projection_type                                                  
  14: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  15: <smallvec::SmallVec<A> as core::iter::traits::FromIterator<<A as smallvec::Array>::Item>>::from_iter
  16: rustc::ty::fold::TypeFoldable::fold_with                                                           
  17: rustc::ty::fold::TypeFoldable::fold_with                                                           
  18: rustc::ty::fold::TypeFoldable::fold_with                                                           
  19: rustc::traits::project::normalize                                                                  
  20: rustc::infer::InferCtxt::partially_normalize_associated_types_in                                   
  21: rustc_typeck::check::FnCtxt::instantiate_bounds                                                    
  22: rustc_typeck::check::FnCtxt::instantiate_value_path                                                
  23: rustc_typeck::check::FnCtxt::check_expr_kind                                                       
  24: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_needs                                 
  25: rustc::ty::context::tls::with_related_context                                                      
  26: rustc::infer::InferCtxtBuilder::enter                                                              
  27: rustc_typeck::check::typeck_tables_of                                                              
  28: rustc::ty::query::__query_compute::typeck_tables_of                                                
  29: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::typeck_tables_of<'tcx>>::compute
  30: rustc::ty::context::tls::with_context                                                              
  31: rustc::dep_graph::graph::DepGraph::with_task_impl                                                  
  32: rustc::ty::context::tls::with_related_context                                                      
  33: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  34: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query         
  35: rustc::ty::query::plumbing::force_from_dep_node                                                    
  36: rustc::dep_graph::graph::DepGraph::try_mark_green                                                  
  37: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_mark_green_and_read
  38: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query           
  39: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_const
  40: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  41: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  42: rustc::traits::project::opt_normalize_projection_type                                              
  43: rustc::traits::project::normalize_projection_type                                                  
  44: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  45: rustc::ty::fold::TypeFoldable::fold_with                                                           
  46: rustc::ty::fold::TypeFoldable::fold_with                                                           
  47: rustc::traits::project::normalize                                                                  
  48: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &'a mut F>::call_once         
  49: <core::iter::FlatMap<I, U, F> as core::iter::iterator::Iterator>::next                             
  50: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter                                    
  51: rustc::ty::wf::WfPredicates::normalize                                                             
  52: rustc::ty::wf::trait_obligations                                                                   
  53: rustc::ty::context::tls::with_related_context                                                      
  54: rustc::infer::InferCtxtBuilder::enter                                                              
  55: rustc_typeck::check::wfcheck::check_item_well_formed                                               
  56: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::check_item_well_formed<'tcx>>::compute
  57: rustc::ty::context::tls::with_context                                                              
  58: rustc::dep_graph::graph::DepGraph::with_task_impl                                                  
  59: rustc::ty::context::tls::with_related_context                                                      
  60: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  61: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query           
  62: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::ensure_query        
  63: rustc::hir::Crate::visit_all_item_likes                                                            
  64: rustc::session::Session::track_errors                                                              
  65: rustc_typeck::check_crate                                                                          
  66: rustc::ty::context::tls::enter_context                                                             
  67: <std::thread::local::LocalKey<T>>::with                                                            
  68: rustc::ty::context::TyCtxt::create_and_enter                                                       
  69: rustc_driver::driver::compile_input                                                                
  70: rustc_driver::run_compiler_with_pool                                                               
  71: rustc_driver::driver::spawn_thread_pool                                                            
  72: rustc_driver::run_compiler                                                                         
  73: <scoped_tls::ScopedKey<T>>::set                                                                    
  74: syntax::with_globals                                                                               
  75: __rust_maybe_catch_panic                                                                           
             at libpanic_unwind/lib.rs:102                                                               
  76: rustc_driver::run                                                                                  
  77: rustc_driver::main                                                                                 
  78: std::rt::lang_start::{{closure}}                                                                   
  79: std::panicking::try::do_call                                                                       
             at libstd/rt.rs:59                                                                          
             at libstd/panicking.rs:310                                                                  
  80: __rust_maybe_catch_panic                                                                           
             at libpanic_unwind/lib.rs:102                                                               
  81: std::rt::lang_start_internal                                                                       
             at libstd/panicking.rs:289                                                                  
             at libstd/panic.rs:392                                                                      
             at libstd/rt.rs:58                                                                          
  82: main                                                                                               
  83: __libc_start_main                                                                                  
  84: <unknown>                                                                                          
query stack during panic:                                                                                
#0 [typeck_tables_of] processing `<str as Tr>::Arr::{{constant}}`                                        
#1 [check_item_well_formed] processing `<str as Tr>`                                                     
end of query stack                                                                                       
                                                                                                         
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 1.30.0-nightly (2224a42c3 2018-09-17) running on x86_64-unknown-linux-gnu                    
                                                                                                         
note: compiler flags: -C debuginfo=2 -C incremental --crate-type lib                                     
                                                                                                         
note: some of the compiler flags provided by cargo are hidden                                            
                                                                                                         
error: Could not compile `associated-const`.                                                             

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