Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

impossible case reached on lifetime inference for impl Trait in return position #49926

Closed
nivkner opened this issue Apr 13, 2018 · 2 comments
Closed
Labels
A-impl-trait Area: `impl Trait`. Universally / existentially quantified anonymous types with static dispatch. C-bug Category: This is a bug. I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️ regression-from-stable-to-beta Performance or correctness regression from stable to beta. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
Milestone

Comments

@nivkner
Copy link
Contributor

nivkner commented Apr 13, 2018

summery

when the inferred associated types of the trait contain lifetimes, the compiler produces an internal error

details

I tried this code:

fn iter() -> impl Iterator {
    (1..2).map(|_| "hello")
}

I expected to see this happen:
the return type is inferred to be impl Iterator<Item=&'static str>,
which, when written like that, is accepted by the compiler.

Instead, this happened:

error: internal compiler error: librustc/infer/error_reporting/mod.rs:184: impossible case reached

thread 'main' panicked at 'Box<Any>', librustc_errors/lib.rs:542:9
note: Run with `RUST_BACKTRACE=1` for a backtrace.
error: aborting due to previous error

Meta

rustc 1.25.0 (84203cac6 2018-03-25)  
binary: rustc                        
commit-hash: 84203cac67e65ca8640b8392348411098c856985
commit-date: 2018-03-25                              
host: x86_64-unknown-linux-gnu                      
release: 1.25.0                                       
LLVM version: 6.0
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:206
   3: std::panicking::default_hook
             at libstd/panicking.rs:222
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:401
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::bug
   8: rustc::session::opt_span_bug_fmt::{{closure}}
   9: rustc::ty::context::tls::with_opt::{{closure}}
  10: rustc::ty::context::tls::with_context_opt
  11: rustc::ty::context::tls::with_opt
  12: rustc::session::opt_span_bug_fmt
  13: rustc::session::bug_fmt
  14: rustc::infer::error_reporting::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::msg_span_from_free_region
  15: <rustc::infer::anon_types::ReverseMapper<'cx, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_region
  16: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  17: <rustc::infer::anon_types::ReverseMapper<'cx, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  18: <rustc_data_structures::accumulate_vec::AccumulateVec<A> as core::iter::traits::FromIterator<<A as rustc_data_structures::array_vec::Array>::Element>>::from_iter
  19: rustc::ty::fold::TypeFoldable::fold_with
  20: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  21: <rustc::infer::anon_types::ReverseMapper<'cx, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  22: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &'a mut F>::call_once
  23: <rustc_data_structures::accumulate_vec::AccumulateVec<A> as core::iter::traits::FromIterator<<A as rustc_data_structures::array_vec::Array>::Element>>::from_iter
  24: <T as rustc::ty::context::InternIteratorElement<T, R>>::intern_with
  25: <rustc::infer::anon_types::ReverseMapper<'cx, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  26: <rustc_data_structures::accumulate_vec::AccumulateVec<A> as core::iter::traits::FromIterator<<A as rustc_data_structures::array_vec::Array>::Element>>::from_iter
  27: rustc::ty::fold::TypeFoldable::fold_with
  28: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  29: <rustc::infer::anon_types::ReverseMapper<'cx, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  30: rustc::infer::anon_types::<impl rustc::infer::InferCtxt<'a, 'gcx, 'tcx>>::infer_anon_definition_from_instantiation
  31: rustc_typeck::check::writeback::WritebackCx::visit_anon_types
  32: rustc_typeck::check::writeback::<impl rustc_typeck::check::FnCtxt<'a, 'gcx, 'tcx>>::resolve_type_vars_in_body
  33: rustc::ty::context::tls::with_related_context
  34: rustc::infer::InferCtxtBuilder::enter
  35: rustc_typeck::check::typeck_tables_of
  36: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::compute_result
  37: rustc::dep_graph::graph::DepGraph::with_task_impl
  38: rustc::ty::context::tls::with_related_context
  39: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::force_with_lock
  40: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::try_get          
  41: rustc::ty::maps::TyCtxtAt::typeck_tables_of                                                 
  42: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::ensure           
  43: rustc::session::Session::track_errors                                                 
  44: rustc_typeck::check::typeck_item_bodies                                               
  45: rustc::dep_graph::graph::DepGraph::with_task_impl                                        
  46: rustc::ty::context::tls::with_related_context                                    
  47: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::force_with_lock
  48: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::try_get        
  49: rustc::ty::maps::TyCtxtAt::typeck_item_bodies                                      
  50: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_item_bodies
  51: rustc_typeck::check_crate                                                             
  52: rustc::ty::context::tls::enter_context       
  53: <std::thread::local::LocalKey<T>>::with                                                    
  54: rustc::ty::context::TyCtxt::create_and_enter                                       
  55: rustc_driver::driver::compile_input          
  56: rustc_driver::run_compiler_impl                                                       
  57: syntax::with_globals             
  58: rustc_driver::run                     
  59: rustc_driver::main                           
  60: std::rt::lang_start::{{closure}}              
  61: std::panicking::try::do_call             
             at libstd/rt.rs:59        
             at libstd/panicking.rs:305
  62: __rust_maybe_catch_panic               
             at libpanic_unwind/lib.rs:101                                                                       
  63: std::rt::lang_start_internal                                                                                      
             at libstd/panicking.rs:284                                                                                      
             at libstd/panic.rs:361                                                                                 
             at libstd/rt.rs:58                                                                                                                                        
  64: main                                    
  65: __libc_start_main                                                                                                      
  66: <unknown>                                                                                                     
query stack during panic:                                                                       
#0 [typeck_tables_of] processing `iter`                                                                                                                                
 --> src/main.rs:1:1                                                     
  |                                                                                                                 
1 | fn iter() -> impl Iterator {                                                                                                                                       
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^                      
#1 [typeck_item_bodies] type-checking all item bodies                                                                        
end of query stack
@pietroalbini pietroalbini added regression-from-stable-to-beta Performance or correctness regression from stable to beta. I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️ I-nominated T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. A-impl-trait Area: `impl Trait`. Universally / existentially quantified anonymous types with static dispatch. C-bug Category: This is a bug. labels Apr 20, 2018
@pietroalbini
Copy link
Member

Can we get this fixed before it hits stable @rust-lang/compiler?

@pietroalbini pietroalbini added this to the 1.26 milestone Apr 20, 2018
@sinkuu
Copy link
Contributor

sinkuu commented Apr 21, 2018

Since the same bug!() is invoked and it compiles fine on Nightly, I guess this is the one fixed by #49730 (which is being beta-backported in #50127).

@nivkner nivkner closed this as completed Apr 21, 2018
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Labels
A-impl-trait Area: `impl Trait`. Universally / existentially quantified anonymous types with static dispatch. C-bug Category: This is a bug. I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️ regression-from-stable-to-beta Performance or correctness regression from stable to beta. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
Projects
None yet
Development

No branches or pull requests

3 participants