ICE: const-prop encountered formatting error: unsized locals are not supported

[tmiasko]

Code

#![feature(unsized_fn_params)]
pub fn f(mut x: [i32]) {
    x[0] = 1;
}

Meta

rustc --version --verbose:

rustc 1.71.0-nightly (a77c55248 2023-05-06)
binary: rustc
commit-hash: a77c552485a19245a266bc03c450676c666b605f
commit-date: 2023-05-06
host: x86_64-unknown-linux-gnu
release: 1.71.0-nightly
LLVM version: 16.0.2

Error

Backtrace

thread 'rustc' panicked at 'const-prop encountered formatting error: unsized locals are not supported', compiler/rustc_mir_transform/src/const_prop_lint.rs:271:17
stack backtrace:
   0:     0x7f832bf690d1 - std::backtrace_rs::backtrace::libunwind::trace::h748efa8d196594ea
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f832bf690d1 - std::backtrace_rs::backtrace::trace_unsynchronized::hba1b195853d9d394
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f832bf690d1 - std::sys_common::backtrace::_print_fmt::hf5baf2e14c45ba0c
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f832bf690d1 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hbf761e313ca3ada9
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f832bfc9d9f - core::fmt::rt::Argument::fmt::h9a4b2d89a60be8da
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/core/src/fmt/rt.rs:138:9
   5:     0x7f832bfc9d9f - core::fmt::write::h66441248ae33813a
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/core/src/fmt/mod.rs:1094:21
   6:     0x7f832bf5c1b1 - std::io::Write::write_fmt::ha691d967a2ddc69c
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/io/mod.rs:1712:15
   7:     0x7f832bf68ee5 - std::sys_common::backtrace::_print::hdcec4f4c10a19269
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f832bf68ee5 - std::sys_common::backtrace::print::ha30bc382982a7953
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f832bf6bb77 - std::panicking::default_hook::{{closure}}::hcc3f39fea9e4a023
  10:     0x7f832bf6b964 - std::panicking::default_hook::h126f3b7e37854051
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/panicking.rs:288:9
  11:     0x7f832f17850b - <rustc_driver_impl[aec4a7513f090b1c]::install_ice_hook::{closure#0} as core[f726735fcfc4c81f]::ops::function::FnOnce<(&core[f726735fcfc4c81f]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  12:     0x7f832bf6c297 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h6b1f581dc385c03f
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/alloc/src/boxed.rs:1999:9
  13:     0x7f832bf6c297 - std::panicking::rust_panic_with_hook::ha3a27ba12ace114b
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/panicking.rs:695:13
  14:     0x7f832bf6c017 - std::panicking::begin_panic_handler::{{closure}}::h6db61a38b58c99ee
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/panicking.rs:582:13
  15:     0x7f832bf69516 - std::sys_common::backtrace::__rust_end_short_backtrace::h281ac153d73a34fc
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/sys_common/backtrace.rs:150:18
  16:     0x7f832bf6bd82 - rust_begin_unwind
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/panicking.rs:578:5
  17:     0x7f832bfc6023 - core::panicking::panic_fmt::h44f915e75f789b36
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/core/src/panicking.rs:67:14
  18:     0x7f832e179408 - <rustc_mir_transform[2ef7e3d9e9a6caf7]::const_prop_lint::ConstPropagator as rustc_middle[3ab9e3af7de3f1b4]::mir::visit::Visitor>::visit_basic_block_data
  19:     0x7f832e16af62 - <rustc_mir_transform[2ef7e3d9e9a6caf7]::const_prop_lint::ConstProp as rustc_mir_transform[2ef7e3d9e9a6caf7]::pass_manager::MirLint>::run_lint
  20:     0x7f832e49b16f - rustc_mir_transform[2ef7e3d9e9a6caf7]::mir_drops_elaborated_and_const_checked
  21:     0x7f832e4995f8 - rustc_query_system[917e91cab306a717]::query::plumbing::try_execute_query::<rustc_query_impl[43a49a3d2918852e]::queries::mir_drops_elaborated_and_const_checked, rustc_query_impl[43a49a3d2918852e]::plumbing::QueryCtxt>
  22:     0x7f832e612b3e - rustc_interface[8020cbc989be0ea1]::passes::analysis
  23:     0x7f832e902d07 - rustc_query_system[917e91cab306a717]::query::plumbing::try_execute_query::<rustc_query_impl[43a49a3d2918852e]::queries::analysis, rustc_query_impl[43a49a3d2918852e]::plumbing::QueryCtxt>
  24:     0x7f832e902a23 - rustc_query_impl[43a49a3d2918852e]::get_query::analysis
  25:     0x7f832e3a861f - <rustc_middle[3ab9e3af7de3f1b4]::ty::context::GlobalCtxt>::enter::<rustc_driver_impl[aec4a7513f090b1c]::run_compiler::{closure#1}::{closure#2}::{closure#4}, core[f726735fcfc4c81f]::result::Result<(), rustc_span[bfe87b81068afb7a]::ErrorGuaranteed>>
  26:     0x7f832e3a780f - <rustc_interface[8020cbc989be0ea1]::interface::Compiler>::enter::<rustc_driver_impl[aec4a7513f090b1c]::run_compiler::{closure#1}::{closure#2}, core[f726735fcfc4c81f]::result::Result<core[f726735fcfc4c81f]::option::Option<rustc_interface[8020cbc989be0ea1]::queries::Linker>, rustc_span[bfe87b81068afb7a]::ErrorGuaranteed>>
  27:     0x7f832e3a58b1 - rustc_span[bfe87b81068afb7a]::set_source_map::<core[f726735fcfc4c81f]::result::Result<(), rustc_span[bfe87b81068afb7a]::ErrorGuaranteed>, rustc_interface[8020cbc989be0ea1]::interface::run_compiler<core[f726735fcfc4c81f]::result::Result<(), rustc_span[bfe87b81068afb7a]::ErrorGuaranteed>, rustc_driver_impl[aec4a7513f090b1c]::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
  28:     0x7f832e3a4f60 - std[e4b786b2c1bf012e]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[8020cbc989be0ea1]::util::run_in_thread_pool_with_globals<rustc_interface[8020cbc989be0ea1]::interface::run_compiler<core[f726735fcfc4c81f]::result::Result<(), rustc_span[bfe87b81068afb7a]::ErrorGuaranteed>, rustc_driver_impl[aec4a7513f090b1c]::run_compiler::{closure#1}>::{closure#0}, core[f726735fcfc4c81f]::result::Result<(), rustc_span[bfe87b81068afb7a]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[f726735fcfc4c81f]::result::Result<(), rustc_span[bfe87b81068afb7a]::ErrorGuaranteed>>
  29:     0x7f832ea6b3e5 - <<std[e4b786b2c1bf012e]::thread::Builder>::spawn_unchecked_<rustc_interface[8020cbc989be0ea1]::util::run_in_thread_pool_with_globals<rustc_interface[8020cbc989be0ea1]::interface::run_compiler<core[f726735fcfc4c81f]::result::Result<(), rustc_span[bfe87b81068afb7a]::ErrorGuaranteed>, rustc_driver_impl[aec4a7513f090b1c]::run_compiler::{closure#1}>::{closure#0}, core[f726735fcfc4c81f]::result::Result<(), rustc_span[bfe87b81068afb7a]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[f726735fcfc4c81f]::result::Result<(), rustc_span[bfe87b81068afb7a]::ErrorGuaranteed>>::{closure#1} as core[f726735fcfc4c81f]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  30:     0x7f832bf76775 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hcf250329e90c3f77
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/alloc/src/boxed.rs:1985:9
  31:     0x7f832bf76775 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h3a648c216d9fc25d
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/alloc/src/boxed.rs:1985:9
  32:     0x7f832bf76775 - std::sys::unix::thread::Thread::new::thread_start::ha9800a047bb8dea3
                               at /rustc/a77c552485a19245a266bc03c450676c666b605f/library/std/src/sys/unix/thread.rs:108:17
  33:     0x7f832bd1afd4 - start_thread
                               at ./nptl/pthread_create.c:442:8
  34:     0x7f832bd9b5bc - __GI___clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:81
  35:                0x0 - <unknown>

error: 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 1.71.0-nightly (a77c55248 2023-05-06) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib

query stack during panic:
#0 [mir_drops_elaborated_and_const_checked] elaborating drops for `f`
#1 [analysis] running analysis passes on this crate
end of query stack

[RalfJung]

This got fixed as a side-effect of #114011. #114543 will add a test.