ICE: compiler/rustc_mir/src/interpret/eval_context.rs:188:17: The type checker should prevent reading from a never-written local

[chengniansun]

Code

union Foo {
    a: isize,
    b: &VTable,
}
enum Bar {
    Boo = [Foo { b: () }.a][3],
}

Meta

rustc --version --verbose:

rustc 1.53.0-nightly (52e3dffa5 2021-03-25)
binary: rustc
commit-hash: 52e3dffa50cfffdcfa145c0cc0ba48b49abc0c07
commit-date: 2021-03-25
host: x86_64-unknown-linux-gnu
release: 1.53.0-nightly
LLVM version: 12.0.0

Error output

error[E0412]: cannot find type `VTable` in this scope
 --> perses_node_priority_with_dfs_delta_reduced_mutant.rs:3:9
  |
3 |     b: &VTable,
  |         ^^^^^^ not found in this scope

error[E0601]: `main` function not found in crate `perses_node_priority_with_dfs_delta_reduced_mutant`
 --> perses_node_priority_with_dfs_delta_reduced_mutant.rs:1:1
  |
1 | / union Foo {
2 | |     a: isize,
3 | |     b: &VTable,
4 | | }
5 | | enum Bar {
6 | |     Boo = [Foo { b: () }.a][3],
7 | | }
  | |_^ consider adding a `main` function to `perses_node_priority_with_dfs_delta_reduced_mutant.rs`

error[E0106]: missing lifetime specifier
 --> perses_node_priority_with_dfs_delta_reduced_mutant.rs:3:8
  |
3 |     b: &VTable,
  |        ^ expected named lifetime parameter
  |
help: consider introducing a named lifetime parameter
  |
1 | union Foo<'a> {
2 |     a: isize,
3 |     b: &'a VTable,
  |

error[E0658]: unions with non-`Copy` fields other than `ManuallyDrop<T>` are unstable
 --> perses_node_priority_with_dfs_delta_reduced_mutant.rs:3:5
  |
3 |     b: &VTable,
  |     ^^^^^^^^^^
  |
  = note: see issue #55149 <https://github.com/rust-lang/rust/issues/55149> for more information
  = help: add `#![feature(untagged_unions)]` to the crate attributes to enable

error: internal compiler error: compiler/rustc_mir/src/interpret/eval_context.rs:188:17: The type checker should prevent reading from a never-written local

thread 'rustc' panicked at 'Box<Any>', /rustc/52e3dffa50cfffdcfa145c0cc0ba48b49abc0c07/library/std/src/panic.rs:59:5
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 1.53.0-nightly (52e3dffa5 2021-03-25) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [eval_to_allocation_raw] const-evaluating + checking `Bar::Boo::{constant#0}`
#1 [eval_to_const_value_raw] simplifying constant for the type system `Bar::Boo::{constant#0}`
end of query stack
error: aborting due to 5 previous errors

Some errors have detailed explanations: E0106, E0412, E0601, E0658.
For more information about an error, try `rustc --explain E0106`.

Backtrace

error[E0412]: cannot find type `VTable` in this scope
 --> perses_node_priority_with_dfs_delta_reduced_mutant.rs:3:9
  |
3 |     b: &VTable,
  |         ^^^^^^ not found in this scope

error[E0601]: `main` function not found in crate `perses_node_priority_with_dfs_delta_reduced_mutant`
 --> perses_node_priority_with_dfs_delta_reduced_mutant.rs:1:1
  |
1 | / union Foo {
2 | |     a: isize,
3 | |     b: &VTable,
4 | | }
5 | | enum Bar {
6 | |     Boo = [Foo { b: () }.a][3],
7 | | }
  | |_^ consider adding a `main` function to `perses_node_priority_with_dfs_delta_reduced_mutant.rs`

error[E0106]: missing lifetime specifier
 --> perses_node_priority_with_dfs_delta_reduced_mutant.rs:3:8
  |
3 |     b: &VTable,
  |        ^ expected named lifetime parameter
  |
help: consider introducing a named lifetime parameter
  |
1 | union Foo<'a> {
2 |     a: isize,
3 |     b: &'a VTable,
  |

error[E0658]: unions with non-`Copy` fields other than `ManuallyDrop<T>` are unstable
 --> perses_node_priority_with_dfs_delta_reduced_mutant.rs:3:5
  |
3 |     b: &VTable,
  |     ^^^^^^^^^^
  |
  = note: see issue #55149 <https://github.com/rust-lang/rust/issues/55149> for more information
  = help: add `#![feature(untagged_unions)]` to the crate attributes to enable

error: internal compiler error: compiler/rustc_mir/src/interpret/eval_context.rs:188:17: The type checker should prevent reading from a never-written local

thread 'rustc' panicked at 'Box<Any>', /rustc/52e3dffa50cfffdcfa145c0cc0ba48b49abc0c07/library/std/src/panic.rs:59:5
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: rustc_mir::interpret::operand::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::access_local
   8: rustc_mir::interpret::operand::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::eval_operand
   9: rustc_mir::interpret::step::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::eval_rvalue_into_place
  10: rustc_mir::interpret::step::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::run
  11: rustc_mir::const_eval::eval_queries::eval_to_allocation_raw_provider
  12: rustc_query_impl::<impl rustc_query_system::query::config::QueryAccessors<rustc_query_impl::plumbing::QueryCtxt> for rustc_query_impl::queries::eval_to_allocation_raw>::compute
  13: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  14: rustc_data_structures::stack::ensure_sufficient_stack
  15: rustc_query_system::query::plumbing::force_query_with_job
  16: rustc_query_system::query::plumbing::get_query_impl
  17: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::eval_to_allocation_raw
  18: rustc_mir::const_eval::eval_queries::eval_to_const_value_raw_provider
  19: rustc_query_impl::<impl rustc_query_system::query::config::QueryAccessors<rustc_query_impl::plumbing::QueryCtxt> for rustc_query_impl::queries::eval_to_const_value_raw>::compute
  20: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  21: rustc_data_structures::stack::ensure_sufficient_stack
  22: rustc_query_system::query::plumbing::force_query_with_job
  23: rustc_query_system::query::plumbing::get_query_impl
  24: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::eval_to_const_value_raw
  25: rustc_mir::const_eval::eval_queries::eval_to_const_value_raw_provider
  26: rustc_query_impl::<impl rustc_query_system::query::config::QueryAccessors<rustc_query_impl::plumbing::QueryCtxt> for rustc_query_impl::queries::eval_to_const_value_raw>::compute
  27: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  28: rustc_data_structures::stack::ensure_sufficient_stack
  29: rustc_query_system::query::plumbing::force_query_with_job
  30: rustc_query_system::query::plumbing::get_query_impl
  31: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::eval_to_const_value_raw
  32: rustc_middle::mir::interpret::queries::<impl rustc_middle::ty::context::TyCtxt>::const_eval_global_id
  33: rustc_middle::mir::interpret::queries::<impl rustc_middle::ty::context::TyCtxt>::const_eval_poly
  34: rustc_typeck::collect::convert_item
  35: <rustc_typeck::collect::CollectItemTypesVisitor as rustc_hir::intravisit::Visitor>::visit_item
  36: rustc_middle::hir::map::Map::visit_item_likes_in_module
  37: rustc_typeck::collect::collect_mod_item_types
  38: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  39: rustc_query_system::query::plumbing::force_query_with_job
  40: rustc_query_system::query::plumbing::get_query_impl
  41: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::collect_mod_item_types
  42: rustc_session::session::Session::track_errors
  43: rustc_typeck::check_crate
  44: rustc_interface::passes::analysis
  45: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  46: rustc_data_structures::stack::ensure_sufficient_stack
  47: rustc_query_system::query::plumbing::force_query_with_job
  48: rustc_query_system::query::plumbing::get_query_impl
  49: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis
  50: rustc_interface::passes::QueryContext::enter
  51: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  52: rustc_span::with_source_map
  53: rustc_interface::interface::create_compiler_and_run
  54: scoped_tls::ScopedKey<T>::set
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 1.53.0-nightly (52e3dffa5 2021-03-25) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [eval_to_allocation_raw] const-evaluating + checking `Bar::Boo::{constant#0}`
#1 [eval_to_const_value_raw] simplifying constant for the type system `Bar::Boo::{constant#0}`
#2 [eval_to_const_value_raw] simplifying constant for the type system `Bar::Boo::{constant#0}`
#3 [collect_mod_item_types] collecting item types in top-level module
#4 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 5 previous errors

Some errors have detailed explanations: E0106, E0412, E0601, E0658.
For more information about an error, try `rustc --explain E0106`.

[chengniansun]

This might be relevant to or a duplicate of #69487

[chengniansun]

Besides, I finally trigged this hidden rustc feature.

Code

fn main() {
    break rust;
}

Meta

rustc --version --verbose:

rustc 1.53.0-nightly (52e3dffa5 2021-03-25)
binary: rustc
commit-hash: 52e3dffa50cfffdcfa145c0cc0ba48b49abc0c07
commit-date: 2021-03-25
host: x86_64-unknown-linux-gnu
release: 1.53.0-nightly
LLVM version: 12.0.0

Error output

error[E0425]: cannot find value `rust` in this scope
 --> perses_node_priority_with_dfs_delta_reduced_mutant.rs:2:11
  |
2 |     break rust;
  |           ^^^^ not found in this scope

error[E0268]: `break` outside of a loop
 --> perses_node_priority_with_dfs_delta_reduced_mutant.rs:2:5
  |
2 |     break rust;
  |     ^^^^^^^^^^ cannot `break` outside of a loop

error: internal compiler error: It looks like you're trying to break rust; would you like some ICE?

note: the compiler expectedly panicked. this is a feature.

note: we would appreciate a joke overview: https://github.com/rust-lang/rust/issues/43162#issuecomment-320764675

note: rustc 1.53.0-nightly (52e3dffa5 2021-03-25) running on x86_64-unknown-linux-gnu

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0268, E0425.
For more information about an error, try `rustc --explain E0268`.

Backtrace

error[E0425]: cannot find value `rust` in this scope
 --> perses_node_priority_with_dfs_delta_reduced_mutant.rs:2:11
  |
2 |     break rust;
  |           ^^^^ not found in this scope

error[E0268]: `break` outside of a loop
 --> perses_node_priority_with_dfs_delta_reduced_mutant.rs:2:5
  |
2 |     break rust;
  |     ^^^^^^^^^^ cannot `break` outside of a loop

error: internal compiler error: It looks like you're trying to break rust; would you like some ICE?

note: the compiler expectedly panicked. this is a feature.

note: we would appreciate a joke overview: https://github.com/rust-lang/rust/issues/43162#issuecomment-320764675

note: rustc 1.53.0-nightly (52e3dffa5 2021-03-25) running on x86_64-unknown-linux-gnu

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0268, E0425.
For more information about an error, try `rustc --explain E0268`.

[JohnTitor]

Assigning P-medium as discussed as part of the Prioritization Working Group procedure and removing I-prioritize.

[RalfJung]

Yeah this very much looks like a duplicate of #69487.