Using associated constant as array size leads to ICE

[rizakrko]

This is a repro case for #52462.
Following code:

trait T {
    const SIZE: usize;
    fn convert(self) -> [u8; T::SIZE];
}

impl T for u64 {
    const SIZE: usize = 8;
    fn convert(self) -> [u8; u64::SIZE] {
        unimplemented!()
    }
}
fn main() {}

causes compilation error:

error[E0283]: type annotations required: cannot resolve `_: T`
 --> src/main.rs:3:30
  |
3 |     fn convert(self) -> [u8; T::SIZE];
  |                              ^^^^^^^
  |
note: required by `T::SIZE`
 --> src/main.rs:2:5
  |
2 |     const SIZE: usize;
  |     ^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

However, change from

fn convert(self) -> [u8; u64::SIZE] {

to

fn convert(self) -> [u8; T::SIZE] {

causes following ICE:

error: internal compiler error: librustc/traits/codegen/mod.rs:63: Encountered ambiguity selecting `Binder(<[type error] as T>)` during codegen, presuming due to overflow

thread 'main' panicked at 'Box<Any>', librustc_errors/lib.rs:578:9

This can be reproduced on stable, beta and nightly. Playground

Meta

rustc 1.30.0-nightly (3edb355 2018-08-03)
binary: rustc
commit-hash: 3edb355
commit-date: 2018-08-03
host: x86_64-unknown-linux-gnu
release: 1.30.0-nightly
LLVM version: 7.0

Backtrace

``` thread 'main' panicked at 'Box', librustc_errors/lib.rs:578:9 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:479 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::ty::context::tls::with_related_context 15: rustc::traits::codegen::codegen_fulfill_obligation 16: rustc::ty::query::__query_compute::codegen_fulfill_obligation 17: rustc::ty::query:: for rustc::ty::query::queries::codegen_fulfill_obligation<'tcx>>::compute 18: rustc::ty::context::tls::with_context 19: rustc::dep_graph::graph::DepGraph::with_task_impl 20: rustc::ty::context::tls::with_related_context 21: rustc::ty::query::plumbing::>::force_query_with_job 22: rustc::ty::query::plumbing::>::get_query 23: rustc::ty::instance::Instance::resolve 24: >::resolve 25: >::const_to_value 26: rustc_mir::transform::const_prop::ConstPropagator::eval_constant 27: as rustc::mir::visit::Visitor<'tcx>>::visit_statement 28: ::run_pass 29: rustc_mir::transform::optimized_mir::{{closure}} 30: rustc_mir::transform::optimized_mir 31: rustc::ty::query::__query_compute::optimized_mir 32: rustc::ty::query:: for rustc::ty::query::queries::optimized_mir<'tcx>>::compute 33: rustc::ty::context::tls::with_context 34: rustc::dep_graph::graph::DepGraph::with_task_impl 35: rustc::ty::context::tls::with_related_context 36: rustc::ty::query::plumbing::>::force_query_with_job 37: rustc::ty::query::plumbing::>::try_get_query 38: rustc::ty::>::maybe_optimized_mir 39: >::load_mir 40: rustc_mir::interpret::const_eval::eval_body_using_ecx 41: rustc_mir::interpret::const_eval::const_eval_provider 42: rustc::ty::query::__query_compute::const_eval 43: rustc::ty::query:: for rustc::ty::query::queries::const_eval<'tcx>>::compute 44: rustc::ty::context::tls::with_context 45: rustc::dep_graph::graph::DepGraph::with_task_impl 46: rustc::ty::context::tls::with_related_context 47: rustc::ty::query::plumbing::>::force_query_with_job 48: rustc::ty::query::plumbing::>::get_query 49: as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_const 50: rustc::ty::structural_impls:: for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with 51: as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty 52: as core::iter::traits::FromIterator<::Element>>::from_iter 53: rustc::ty::fold::TypeFoldable::fold_with 54: rustc::infer::InferCtxt::partially_normalize_associated_types_in 55: rustc::ty::context::tls::with_related_context 56: rustc::infer::InferCtxtBuilder::enter 57: rustc_typeck::check::wfcheck::check_associated_item 58: rustc_typeck::check::wfcheck::check_impl_item 59: rustc::ty::query:: for rustc::ty::query::queries::check_impl_item_well_formed<'tcx>>::compute 60: rustc::ty::context::tls::with_context 61: rustc::dep_graph::graph::DepGraph::with_task_impl 62: rustc::ty::context::tls::with_related_context 63: rustc::ty::query::plumbing::>::force_query_with_job 64: rustc::ty::query::plumbing::>::get_query 65: rustc::ty::query::plumbing::>::ensure_query 66: rustc::session::Session::track_errors 67: rustc::util::common::time 68: rustc_typeck::check_crate 69: rustc::ty::context::tls::enter_context 70: >::with 71: rustc::ty::context::TyCtxt::create_and_enter 72: rustc_driver::driver::compile_input 73: rustc_driver::run_compiler_with_pool 74: >::set 75: syntax::with_globals 76: as core::ops::function::FnOnce<()>>::call_once 77: __rust_maybe_catch_panic at libpanic_unwind/lib.rs:105 78: rustc_driver::run 79: rustc_driver::main 80: std::rt::lang_start::{{closure}} 81: std::panicking::try::do_call at libstd/rt.rs:59 at libstd/panicking.rs:310 82: __rust_maybe_catch_panic at libpanic_unwind/lib.rs:105 83: std::rt::lang_start_internal at libstd/panicking.rs:289 at libstd/panic.rs:392 at libstd/rt.rs:58 84: main 85: __libc_start_main 86: query stack during panic: #0 [codegen_fulfill_obligation] checking if `T` fulfills its obligations #1 [optimized_mir] processing `::convert::{{constant}}` #2 [const_eval] const-evaluating `::convert::{{constant}}` #3 [check_impl_item_well_formed] processing `::convert` end of query stack ```

[dtolnay]

Duplicate of #48027.