Compiler panic with incorrect JoinHandle in thread_local var

[morrisonlevi]

Hello,

While trying to figure out how to keep a JoinHandle in a thread-local variable, I tried compiling this incorrect code, and rust crashed. It will not panic if I use a regular static var instead of in a thread_local! block.

Code

use std::sync::atomic::{AtomicBool, Ordering};
use std::time::Duration;

thread_local! {
    static shutting_down: AtomicBool = AtomicBool::new(false);
    static thread_handle: Option<std::thread::JoinHandle<_>> = None;
}

fn activate() {
    thread_handle = std::thread::spawn(|_| {
        shutting_down.with(|b| {
            b.store(true, Ordering::SeqCst);
        });
    });
}

fn deactivate() {
    shutting_down.with(|b| b.store(true, Ordering::SeqCst));
    match thread_handle {
        Some(handle) => handle.join(),
        None => (),
    }
}

fn main() {
    activate();
    std::thread::sleep(Duration::from_secs(4));
    deactivate();
}

Meta

$ rustc --version --verbose
rustc 1.50.0 (cb75ad5db 2021-02-10)
binary: rustc
commit-hash: cb75ad5db02783e8b0222fee363c5f63f7e2cf5b
commit-date: 2021-02-10
host: x86_64-apple-darwin
release: 1.50.0

Error output

   Compiling rust-tmp v0.1.0 (/private/tmp/rust-tmp)
error[E0121]: the type placeholder `_` is not allowed within types on item signatures
 --> src/main.rs:4:1
  |
4 | / thread_local! {
5 | |     static shutting_down: AtomicBool = AtomicBool::new(false);
6 | |     static thread_handle: Option<std::thread::JoinHandle<_>> = None;
7 | | }
  | | ^
  | | |
  | |_not allowed in type signatures
  |   help: replace `_` with the correct type: `__FastLocalKeyInner<[type error]>`
  |
  = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0282]: type annotations needed
 --> src/main.rs:6:64
  |
6 |     static thread_handle: Option<std::thread::JoinHandle<_>> = None;
  |                                                                ^^^^ cannot infer type

error[E0121]: the type placeholder `_` is not allowed within types on item signatures
 --> src/main.rs:6:58
  |
6 |     static thread_handle: Option<std::thread::JoinHandle<_>> = None;
  |                                                          ^ not allowed in type signatures

error[E0121]: the type placeholder `_` is not allowed within types on item signatures
 --> src/main.rs:6:58
  |
4 | / thread_local! {
5 | |     static shutting_down: AtomicBool = AtomicBool::new(false);
6 | |     static thread_handle: Option<std::thread::JoinHandle<_>> = None;
  | |                                                          ^ not allowed in type signatures
7 | | }
  | |_- help: replace with the correct return type: `Option<&Option<JoinHandle<[type error]>>>`

error: internal compiler error: compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs:501:17: cannot relate region: LUB(ReStatic, ReErased)

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 1.50.0 (cb75ad5db 2021-02-10) running on x86_64-apple-darwin

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin

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

query stack during panic:
#0 [diagnostic_only_typeck] type-checking `thread_handle`
#1 [type_of] computing type of `thread_handle`
#2 [collect_mod_item_types] collecting item types in top-level module
#3 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 5 previous errors

Some errors have detailed explanations: E0121, E0282.
For more information about an error, try `rustc --explain E0121`.
error: could not compile `rust-tmp`

To learn more, run the command again with --verbose.

Backtrace

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:958:9
stack backtrace:
   0:        0x10c3030d4 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h34f76b2ca42fab41
   1:        0x10c367ecd - core::fmt::write::h8f13d857463c51c1
   2:        0x10c2f47c6 - std::io::Write::write_fmt::h0a6214ccb1a8468b
   3:        0x10c306d39 - std::panicking::default_hook::{{closure}}::hb14d90e928578cc7
   4:        0x10c3068c0 - std::panicking::default_hook::h460969f1dc8f738d
   5:        0x10dc77718 - rustc_driver::report_ice::h77e24d066f5581ac
   6:        0x10c30751e - std::panicking::rust_panic_with_hook::h28bf9d6c3916221e
   7:        0x1122c7321 - std::panicking::begin_panic::{{closure}}::h0e87840b5c6a9c59
   8:        0x1122c7289 - std::sys_common::backtrace::__rust_end_short_backtrace::h8659a1b4220fd63a
   9:        0x1127042f1 - std::panicking::begin_panic::hc47dd84e1beec546
  10:        0x1122f8d13 - rustc_errors::HandlerInner::bug::h6bbed7e088c34809
  11:        0x1122f7327 - rustc_errors::Handler::bug::h69a183c778d5ab5c
  12:        0x111d1df04 - rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}::h65cee2a5516e95bd
  13:        0x111d19a36 - rustc_middle::ty::context::tls::with_opt::{{closure}}::h3109336967579a63
  14:        0x111d199f3 - rustc_middle::ty::context::tls::with_opt::h747ffbbb3f367dd7
  15:        0x111d1de2b - rustc_middle::util::bug::opt_span_bug_fmt::h33901786874da521
  16:        0x1126e3dbf - rustc_middle::util::bug::bug_fmt::hb55b8e744ef28c0f
  17:        0x111b5e19a - rustc_infer::infer::lexical_region_resolve::LexicalResolver::lub_concrete_regions::h25839f4cb0abe2e5
  18:        0x111b5b7fd - rustc_infer::infer::lexical_region_resolve::LexicalResolver::infer_variable_values::h6d32fa8f3f8f2754
  19:        0x111b59b01 - rustc_infer::infer::lexical_region_resolve::resolve::hcf63f6be23912b63
  20:        0x111b154dd - rustc_infer::infer::InferCtxt::resolve_regions_and_report_errors::hc9caef24111df0da
  21:        0x11033363b - rustc_typeck::check::regionck::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::regionck_expr::haa3793715e7f2998
  22:        0x11057c54a - rustc_infer::infer::InferCtxtBuilder::enter::h219a0127bc30dfa9
  23:        0x1105c4cea - rustc_typeck::check::diagnostic_only_typeck::h364621c3f9d76391
  24:        0x1105b623d - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::diagnostic_only_typeck>::compute::h1f32e05a03f066b6
  25:        0x110462571 - rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps::h871477445a5c3693
  26:        0x1103e4f61 - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl::h03400ef36b8989e6
  27:        0x1104b390f - rustc_data_structures::stack::ensure_sufficient_stack::h38c0e137943d87a2
  28:        0x110386a18 - rustc_query_system::query::plumbing::get_query_impl::hbecd58d42846f8f4
  29:        0x1105d174b - rustc_typeck::collect::type_of::infer_placeholder_type::h22e10397e5ac1d54
  30:        0x1105cefcf - rustc_typeck::collect::type_of::type_of::he2d37f03223ed220
  31:        0x1104ac850 - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::type_of>::compute::h1177527bd609fe45
  32:        0x11045fe49 - rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps::h4005953a1bc6e47b
  33:        0x1103e6461 - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl::h2125767b4b5e2499
  34:        0x1104bb67c - rustc_data_structures::stack::ensure_sufficient_stack::hb47cec0d499cab41
  35:        0x11033efda - rustc_query_system::query::plumbing::get_query_impl::h11eb5153002162a8
  36:        0x1103ac87f - rustc_query_system::query::plumbing::ensure_query_impl::hf9e2988dcb524633
  37:        0x1104e3fb5 - <rustc_typeck::collect::CollectItemTypesVisitor as rustc_hir::intravisit::Visitor>::visit_item::ha5fe187c567fa04e
  38:        0x110408354 - rustc_middle::hir::map::Map::visit_item_likes_in_module::ha83fa66bba1fe8d2
  39:        0x1104e3695 - rustc_typeck::collect::collect_mod_item_types::hde1f69db390f9b7d
  40:        0x1105003dd - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::collect_mod_item_types>::compute::h2ba13d9ebb52cab7
  41:        0x11045dc5a - rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps::h17016b44bff25730
  42:        0x1103ec72f - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl::h4cb97ebae8a3285a
  43:        0x1104bc800 - rustc_data_structures::stack::ensure_sufficient_stack::hc1ed859f375895e8
  44:        0x11036859e - rustc_query_system::query::plumbing::get_query_impl::h6acef74b409bd4f4
  45:        0x1103ab938 - rustc_query_system::query::plumbing::ensure_query_impl::h42b23e091773e4a0
  46:        0x110520fa7 - rustc_typeck::check_crate::h6c812b48d37b63e5
  47:        0x10de538eb - rustc_interface::passes::analysis::h4f77077d0d32c92e
  48:        0x10dcbd30a - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute::h751d24ab2e450beb
  49:        0x10dcbf1c4 - rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps::he6976e5544ffecfa
  50:        0x10dc410ee - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl::h88d3b296bfb5ed36
  51:        0x10dc8596e - rustc_data_structures::stack::ensure_sufficient_stack::hd0a9f62ff4f35515
  52:        0x10dc2f570 - rustc_query_system::query::plumbing::get_query_impl::h1fa86c7589ee7005
  53:        0x10dcbf5aa - rustc_interface::passes::QueryContext::enter::hdda9d64e1568ae83
  54:        0x10dc9b5a1 - rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter::h23c3663acd2f252b
  55:        0x10dc7a8be - rustc_span::with_source_map::had6878a53046d568
  56:        0x10dc9c584 - rustc_interface::interface::create_compiler_and_run::he48253d83781cb39
  57:        0x10dc86a84 - std::sys_common::backtrace::__rust_begin_short_backtrace::hfb8be6fd991a375d
  58:        0x10dc1cc19 - core::ops::function::FnOnce::call_once{{vtable.shim}}::h898af6dc0dda933c
  59:        0x10c3145cd - std::sys::unix::thread::Thread::new::thread_start::he19012de44640be6
  60:     0x7fff6bbc42eb - __pthread_body
  61:     0x7fff6bbc7249 - __pthread_start

[matthiaskrgr]

The ICE happens since 1.44
@rustbot label: +regression-from-stable-to-stable

[apiraino]

@rustbot ping icebreakers-cleanup-crew

can we add a bit more detail and trace where this starts?

[rustbot]

Hey Cleanup Crew ICE-breakers! This bug has been identified as a good
"Cleanup ICE-breaking candidate". In case it's useful, here are some
instructions for tackling these sorts of bugs. Maybe take a look?
Thanks! <3

cc @AminArria @camelid @chrissimpkins @contrun @DutchGhost @elshize @ethanboxx @h-michael @HallerPatrick @hdhoang @hellow554 @henryboisdequin @imtsuki @JamesPatrickGill @kanru @KarlK90 @LeSeulArtichaut @MAdrianMattocks @matheus-consoli @mental32 @nmccarty @Noah-Kennedy @pard68 @PeytonT @pierreN @Redblueflame @RobbieClarken @RobertoSnap @robjtede @SarthakSingh31 @shekohex @sinato @smmalis37 @steffahn @Stupremee @tamuhey @turboladen @woshilapin @yerke

[apiraino]

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

@rustbot label -I-prioritize +P-medium

[hellow554]

Regression between f509b26...f4c675c

If I had to guess, I would say #66131

[hellow554]

Reduced testcase:

thread_local! {
    static thread_handle: _ = 0;
}

fn main() {}