ICE on inline const pattern using const generic parameter

[Esper89]

Using a const parameter in an inline const pattern causes an ICE, but only when you don't directly use the parameter. This seems to be the same problem as #82518, although under different circumstances.

Code

#![feature(inline_const)]
#![feature(generic_const_exprs)]

const fn foo(val: usize) -> usize { val }

fn bar<const N: usize>(num: usize) -> &'static str
where [(); foo(N)]:
{
    match num {
        const { foo(N) } => "fizz",
        _ => "buzz"
    }
}

Using const { N } instead of const { foo(N) } gives

error[E0158]: const parameters cannot be referenced in patterns

Disappointing, but undoubtedly the intended behavior.

The above example wouldn't be easy to come across naturally, but if the const parameter was (for example) an array and you tried to index it, the compiler would tell you to use a const fn to do that. This code causes the same ICE:

#![feature(adt_const_params)]
#![feature(inline_const)]
#![feature(generic_const_exprs)]

const fn get(array: [usize; 5], index: usize) -> usize { array[index] }

fn bar<const A: [usize; 5]>(num: usize) -> &'static str
where [(); get(A, 0)]:
{
    match num {
        const { get(A, 0) } => "fizz",
        _ => "buzz"
    }
}

I should note that this issue is only present with the inline_const feature and the generic_const_exprs feature.

Meta

rustc --version --verbose:

rustc 1.58.0-nightly (efd048394 2021-10-20)
binary: rustc
commit-hash: efd0483949496b067cd5f7569d1b28cd3d5d3c72
commit-date: 2021-10-20
host: x86_64-unknown-linux-gnu
release: 1.58.0-nightly
LLVM version: 13.0.0

Error output

error: internal compiler error: /rustc/efd0483949496b067cd5f7569d1b28cd3d5d3c72/compiler/rustc_middle/src/ty/consts.rs:194:32: expected bits of usize, got Const {
    ty: usize,
    val: Unevaluated(
        Unevaluated {
            def: WithOptConstParam {
                did: DefId(0:62 ~ const_testing_stuff[3d48]::arrays::bar::{constant#2}),
                const_param_did: None,
            },
            substs_: None,
            promoted: None,
        },
    ),
}

Backtrace

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1147:9
stack backtrace:
   0: std::panicking::begin_panic
   1: std::panic::panic_any
   2: rustc_errors::HandlerInner::bug
   3: rustc_errors::Handler::bug
   4: rustc_middle::ty::context::tls::with_opt
   5: rustc_middle::util::bug::opt_span_bug_fmt
   6: rustc_middle::util::bug::bug_fmt
   7: indexmap::map::core::Entry<K,V>::or_insert_with
   8: rustc_mir_build::build::matches::<impl rustc_mir_build::build::Builder>::test_candidates_with_or
   9: rustc_data_structures::stack::ensure_sufficient_stack
  10: rustc_mir_build::build::matches::<impl rustc_mir_build::build::Builder>::lower_match_tree
  11: rustc_mir_build::build::matches::<impl rustc_mir_build::build::Builder>::match_expr
  12: rustc_mir_build::build::expr::into::<impl rustc_mir_build::build::Builder>::expr_into_dest
  13: rustc_mir_build::build::expr::into::<impl rustc_mir_build::build::Builder>::expr_into_dest
  14: rustc_mir_build::build::block::<impl rustc_mir_build::build::Builder>::ast_block_stmts
  15: rustc_mir_build::build::scope::<impl rustc_mir_build::build::Builder>::in_scope
  16: rustc_mir_build::build::expr::into::<impl rustc_mir_build::build::Builder>::expr_into_dest
  17: rustc_mir_build::build::expr::into::<impl rustc_mir_build::build::Builder>::expr_into_dest
  18: rustc_mir_build::build::expr::into::<impl rustc_mir_build::build::Builder>::expr_into_dest
  19: rustc_mir_build::build::construct_fn
  20: rustc_infer::infer::InferCtxtBuilder::enter
  21: rustc_mir_build::build::mir_built
  22: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  23: rustc_data_structures::stack::ensure_sufficient_stack
  24: rustc_query_system::query::plumbing::try_execute_query
  25: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_built
  26: rustc_mir_transform::check_unsafety::unsafety_check_result
  27: core::ops::function::FnOnce::call_once
  28: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  29: rustc_data_structures::stack::ensure_sufficient_stack
  30: rustc_query_system::query::plumbing::try_execute_query
  31: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::unsafety_check_result
  32: rustc_mir_transform::mir_const
  33: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  34: rustc_data_structures::stack::ensure_sufficient_stack
  35: rustc_query_system::query::plumbing::try_execute_query
  36: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_const
  37: rustc_mir_transform::mir_promoted
  38: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  39: rustc_data_structures::stack::ensure_sufficient_stack
  40: rustc_query_system::query::plumbing::try_execute_query
  41: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_promoted
  42: core::ops::function::FnOnce::call_once
  43: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  44: rustc_data_structures::stack::ensure_sufficient_stack
  45: rustc_query_system::query::plumbing::try_execute_query
  46: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_borrowck
  47: rustc_middle::hir::map::Map::par_body_owners
  48: rustc_session::utils::<impl rustc_session::session::Session>::time
  49: rustc_interface::passes::analysis
  50: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  51: rustc_data_structures::stack::ensure_sufficient_stack
  52: rustc_query_system::query::plumbing::try_execute_query
  53: rustc_query_system::query::plumbing::get_query
  54: rustc_interface::passes::QueryContext::enter
  55: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  56: rustc_span::with_source_map
  57: scoped_tls::ScopedKey<T>::set

[nhamovitz]

@rustbot label +A-const-generics