ICE: compiler/rustc_mir_build/src/build/matches/mod.rs `None`

[matthiaskrgr]

auto-reduced (treereduce-rust):

fn split_last(_: &()) -> Option<(&i32, &i32)> {
    None
}

fn assign_twice() {
    loop {
        match () {
            
            (! | !) if let _ = split_last(&()) => {}
            _ => {}
        }
    }
}

original:

//@ check-pass

#![feature(if_let_guard)]

fn split_last(_: &()) -> Option<(&i32, &i32)> {
    None
}

fn assign_twice() {
    loop {
        match () {
            #[allow(irrefutable_let_patterns)]
            (! | !) if let _ = split_last(&()) => {}
            _ => {}
        }
    }
}

fn main() {}

Version information

rustc 1.84.0-nightly (251dc8ad8 2024-11-15)
binary: rustc
commit-hash: 251dc8ad84492c792a7600d8c5fef2ec868a36a7
commit-date: 2024-11-15
host: x86_64-unknown-linux-gnu
release: 1.84.0-nightly
LLVM version: 19.1.3

Possibly related line of code:

rust/compiler/rustc_mir_build/src/build/matches/mod.rs

Lines 1534 to 1546 in 251dc8a

	source_info,
	);
	leaf_candidate.pre_binding_block = Some(new_pre_binding);
	if has_guard {
	// Falsely branch to `next_candidate_start_block` also if the guard fails.
	let new_otherwise = self.cfg.start_new_block();
	let old_otherwise = leaf_candidate.otherwise_block.unwrap();
	self.false_edges(
	new_otherwise,
	old_otherwise,
	next_candidate_start_block,
	source_info,
	);

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output

error[E0658]: `if let` guards are experimental
  --> /tmp/icemaker_global_tempdir.FVFwJhAXzIYI/rustc_testrunner_tmpdir_reporting.RbOs5qNwMqij/mvce.rs:13:21
   |
13 |             (! | !) if let _ = split_last(&()) => {}
   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #51114 <https://github.com/rust-lang/rust/issues/51114> for more information
   = help: add `#![feature(if_let_guard)]` to the crate attributes to enable
   = note: this compiler was built on 2024-11-15; consider upgrading it if it is out of date
   = help: you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`

error[E0658]: `!` patterns are experimental
  --> /tmp/icemaker_global_tempdir.FVFwJhAXzIYI/rustc_testrunner_tmpdir_reporting.RbOs5qNwMqij/mvce.rs:13:14
   |
13 |             (! | !) if let _ = split_last(&()) => {}
   |              ^
   |
   = note: see issue #118155 <https://github.com/rust-lang/rust/issues/118155> for more information
   = help: add `#![feature(never_patterns)]` to the crate attributes to enable
   = note: this compiler was built on 2024-11-15; consider upgrading it if it is out of date

error[E0658]: `!` patterns are experimental
  --> /tmp/icemaker_global_tempdir.FVFwJhAXzIYI/rustc_testrunner_tmpdir_reporting.RbOs5qNwMqij/mvce.rs:13:18
   |
13 |             (! | !) if let _ = split_last(&()) => {}
   |                  ^
   |
   = note: see issue #118155 <https://github.com/rust-lang/rust/issues/118155> for more information
   = help: add `#![feature(never_patterns)]` to the crate attributes to enable
   = note: this compiler was built on 2024-11-15; consider upgrading it if it is out of date

warning: unnecessary parentheses around pattern
  --> /tmp/icemaker_global_tempdir.FVFwJhAXzIYI/rustc_testrunner_tmpdir_reporting.RbOs5qNwMqij/mvce.rs:13:13
   |
13 |             (! | !) if let _ = split_last(&()) => {}
   |             ^     ^
   |
   = note: `#[warn(unused_parens)]` on by default
help: remove these parentheses
   |
13 -             (! | !) if let _ = split_last(&()) => {}
13 +             ! | ! if let _ = split_last(&()) => {}
   |

error: a never pattern is always unreachable
  --> /tmp/icemaker_global_tempdir.FVFwJhAXzIYI/rustc_testrunner_tmpdir_reporting.RbOs5qNwMqij/mvce.rs:13:51
   |
13 |             (! | !) if let _ = split_last(&()) => {}
   |                                                   ^^
   |                                                   |
   |                                                   this will never be executed
   |                                                   help: remove this expression

error[E0601]: `main` function not found in crate `mvce`
  --> /tmp/icemaker_global_tempdir.FVFwJhAXzIYI/rustc_testrunner_tmpdir_reporting.RbOs5qNwMqij/mvce.rs:17:2
   |
17 | }
   |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.FVFwJhAXzIYI/rustc_testrunner_tmpdir_reporting.RbOs5qNwMqij/mvce.rs`

error: mismatched types
  --> /tmp/icemaker_global_tempdir.FVFwJhAXzIYI/rustc_testrunner_tmpdir_reporting.RbOs5qNwMqij/mvce.rs:13:14
   |
13 |             (! | !) if let _ = split_last(&()) => {}
   |              ^ a never pattern must be used on an uninhabited type
   |
   = note: the matched value is of type `()`

error: mismatched types
  --> /tmp/icemaker_global_tempdir.FVFwJhAXzIYI/rustc_testrunner_tmpdir_reporting.RbOs5qNwMqij/mvce.rs:13:18
   |
13 |             (! | !) if let _ = split_last(&()) => {}
   |                  ^ a never pattern must be used on an uninhabited type
   |
   = note: the matched value is of type `()`

warning: irrefutable `if let` guard pattern
  --> /tmp/icemaker_global_tempdir.FVFwJhAXzIYI/rustc_testrunner_tmpdir_reporting.RbOs5qNwMqij/mvce.rs:13:24
   |
13 |             (! | !) if let _ = split_last(&()) => {}
   |                        ^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this pattern will always match, so the guard is useless
   = help: consider removing the guard and adding a `let` inside the match arm
   = note: `#[warn(irrefutable_let_patterns)]` on by default

thread 'rustc' panicked at compiler/rustc_mir_build/src/build/matches/mod.rs:1540:76:
called `Option::unwrap()` on a `None` value
stack backtrace:
   0:     0x79ade605a3ba - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h3e8890c320687803
   1:     0x79ade680414a - core::fmt::write::h8e02e323e721d5d3
   2:     0x79ade7c2cc51 - std::io::Write::write_fmt::hfa5fc2d5ad51eab4
   3:     0x79ade605a212 - std::sys::backtrace::BacktraceLock::print::hef9ddff43c45c466
   4:     0x79ade605c716 - std::panicking::default_hook::{{closure}}::he4ae1ef11715c038
   5:     0x79ade605c560 - std::panicking::default_hook::h4571154760051e3a
   6:     0x79ade50e4281 - std[575dabc3fc23637d]::panicking::update_hook::<alloc[488fcebc54bee2fb]::boxed::Box<rustc_driver_impl[530468506af41d6d]::install_ice_hook::{closure#0}>>::{closure#0}
   7:     0x79ade605ce28 - std::panicking::rust_panic_with_hook::h99e29fee3fbc2974
   8:     0x79ade605cbc6 - std::panicking::begin_panic_handler::{{closure}}::h66e3972102a7eb3e
   9:     0x79ade605a869 - std::sys::backtrace::__rust_end_short_backtrace::ha9860e2cc56614c6
  10:     0x79ade605c8bc - rust_begin_unwind
  11:     0x79ade2adde30 - core::panicking::panic_fmt::h21ce4ecfcb0cf215
  12:     0x79ade2e52c6c - core::panicking::panic::h2175426ea9d4336d
  13:     0x79ade40982f9 - core::option::unwrap_failed::hb947bce75902c03c
  14:     0x79ade6b48ff7 - rustc_mir_build[ce774ae811bc940]::build::matches::traverse_candidate::<&mut rustc_mir_build[ce774ae811bc940]::build::matches::Candidate, (), core[678332cb0ee15b78]::iter::adapters::rev::Rev<core[678332cb0ee15b78]::slice::iter::IterMut<rustc_mir_build[ce774ae811bc940]::build::matches::Candidate>>, <rustc_mir_build[ce774ae811bc940]::build::matches::Candidate>::visit_leaves_rev<<rustc_mir_build[ce774ae811bc940]::build::Builder>::lower_match_tree::{closure#1}>::{closure#0}, <rustc_mir_build[ce774ae811bc940]::build::matches::Candidate>::visit_leaves_rev<<rustc_mir_build[ce774ae811bc940]::build::Builder>::lower_match_tree::{closure#1}>::{closure#1}, <rustc_mir_build[ce774ae811bc940]::build::matches::Candidate>::visit_leaves_rev<<rustc_mir_build[ce774ae811bc940]::build::Builder>::lower_match_tree::{closure#1}>::{closure#2}>
  15:     0x79ade6b485cb - <rustc_mir_build[ce774ae811bc940]::build::Builder>::lower_match_tree
  16:     0x79ade6b26bb2 - <rustc_mir_build[ce774ae811bc940]::build::Builder>::expr_into_dest
  17:     0x79ade6b2804a - <rustc_mir_build[ce774ae811bc940]::build::Builder>::expr_into_dest
  18:     0x79ade748d32b - <rustc_mir_build[ce774ae811bc940]::build::Builder>::ast_block_stmts
  19:     0x79ade748c28c - <rustc_mir_build[ce774ae811bc940]::build::Builder>::ast_block
  20:     0x79ade6b25f0e - <rustc_mir_build[ce774ae811bc940]::build::Builder>::expr_into_dest
  21:     0x79ade6b29dda - <rustc_mir_build[ce774ae811bc940]::build::Builder>::expr_into_dest
  22:     0x79ade6b1cb49 - <rustc_mir_build[ce774ae811bc940]::build::Builder>::as_temp::{closure#0}
  23:     0x79ade6b27dbd - <rustc_mir_build[ce774ae811bc940]::build::Builder>::expr_into_dest
  24:     0x79ade6b2804a - <rustc_mir_build[ce774ae811bc940]::build::Builder>::expr_into_dest
  25:     0x79ade748d32b - <rustc_mir_build[ce774ae811bc940]::build::Builder>::ast_block_stmts
  26:     0x79ade748c28c - <rustc_mir_build[ce774ae811bc940]::build::Builder>::ast_block
  27:     0x79ade6b25f0e - <rustc_mir_build[ce774ae811bc940]::build::Builder>::expr_into_dest
  28:     0x79ade6b2804a - <rustc_mir_build[ce774ae811bc940]::build::Builder>::expr_into_dest
  29:     0x79ade6b378e9 - rustc_mir_build[ce774ae811bc940]::build::mir_build
  30:     0x79ade6807f04 - rustc_mir_transform[b6a0096f646ee25e]::mir_built
  31:     0x79ade6807ec7 - rustc_query_impl[bf1c9f3baad9eabf]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[bf1c9f3baad9eabf]::query_impl::mir_built::dynamic_query::{closure#2}::{closure#0}, rustc_middle[c94631e3827a547d]::query::erase::Erased<[u8; 8usize]>>
  32:     0x79ade6f12001 - rustc_query_system[d5846f7a9cb2c23f]::query::plumbing::try_execute_query::<rustc_query_impl[bf1c9f3baad9eabf]::DynamicConfig<rustc_query_system[d5846f7a9cb2c23f]::query::caches::VecCache<rustc_span[9778d555244491c7]::def_id::LocalDefId, rustc_middle[c94631e3827a547d]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[bf1c9f3baad9eabf]::plumbing::QueryCtxt, false>
  33:     0x79ade6f11bcd - rustc_query_impl[bf1c9f3baad9eabf]::query_impl::mir_built::get_query_non_incr::__rust_end_short_backtrace
  34:     0x79ade2c7bd71 - rustc_mir_build[ce774ae811bc940]::check_unsafety::check_unsafety
  35:     0x79ade703eafd - rustc_query_impl[bf1c9f3baad9eabf]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[bf1c9f3baad9eabf]::query_impl::check_unsafety::dynamic_query::{closure#2}::{closure#0}, rustc_middle[c94631e3827a547d]::query::erase::Erased<[u8; 0usize]>>
  36:     0x79ade703ed9c - rustc_query_system[d5846f7a9cb2c23f]::query::plumbing::try_execute_query::<rustc_query_impl[bf1c9f3baad9eabf]::DynamicConfig<rustc_query_system[d5846f7a9cb2c23f]::query::caches::VecCache<rustc_span[9778d555244491c7]::def_id::LocalDefId, rustc_middle[c94631e3827a547d]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[bf1c9f3baad9eabf]::plumbing::QueryCtxt, false>
  37:     0x79ade703ea41 - rustc_query_impl[bf1c9f3baad9eabf]::query_impl::check_unsafety::get_query_non_incr::__rust_end_short_backtrace
  38:     0x79ade6d4562c - rustc_interface[c18496298df4cf52]::passes::run_required_analyses
  39:     0x79ade762961e - rustc_interface[c18496298df4cf52]::passes::analysis
  40:     0x79ade76295ef - rustc_query_impl[bf1c9f3baad9eabf]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[bf1c9f3baad9eabf]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[c94631e3827a547d]::query::erase::Erased<[u8; 1usize]>>
  41:     0x79ade77dee6e - rustc_query_system[d5846f7a9cb2c23f]::query::plumbing::try_execute_query::<rustc_query_impl[bf1c9f3baad9eabf]::DynamicConfig<rustc_query_system[d5846f7a9cb2c23f]::query::caches::SingleCache<rustc_middle[c94631e3827a547d]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[bf1c9f3baad9eabf]::plumbing::QueryCtxt, false>
  42:     0x79ade77deb4e - rustc_query_impl[bf1c9f3baad9eabf]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  43:     0x79ade76d963a - rustc_interface[c18496298df4cf52]::interface::run_compiler::<core[678332cb0ee15b78]::result::Result<(), rustc_span[9778d555244491c7]::ErrorGuaranteed>, rustc_driver_impl[530468506af41d6d]::run_compiler::{closure#0}>::{closure#1}
  44:     0x79ade7732e50 - std[575dabc3fc23637d]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[c18496298df4cf52]::util::run_in_thread_with_globals<rustc_interface[c18496298df4cf52]::util::run_in_thread_pool_with_globals<rustc_interface[c18496298df4cf52]::interface::run_compiler<core[678332cb0ee15b78]::result::Result<(), rustc_span[9778d555244491c7]::ErrorGuaranteed>, rustc_driver_impl[530468506af41d6d]::run_compiler::{closure#0}>::{closure#1}, core[678332cb0ee15b78]::result::Result<(), rustc_span[9778d555244491c7]::ErrorGuaranteed>>::{closure#0}, core[678332cb0ee15b78]::result::Result<(), rustc_span[9778d555244491c7]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[678332cb0ee15b78]::result::Result<(), rustc_span[9778d555244491c7]::ErrorGuaranteed>>
  45:     0x79ade773326b - <<std[575dabc3fc23637d]::thread::Builder>::spawn_unchecked_<rustc_interface[c18496298df4cf52]::util::run_in_thread_with_globals<rustc_interface[c18496298df4cf52]::util::run_in_thread_pool_with_globals<rustc_interface[c18496298df4cf52]::interface::run_compiler<core[678332cb0ee15b78]::result::Result<(), rustc_span[9778d555244491c7]::ErrorGuaranteed>, rustc_driver_impl[530468506af41d6d]::run_compiler::{closure#0}>::{closure#1}, core[678332cb0ee15b78]::result::Result<(), rustc_span[9778d555244491c7]::ErrorGuaranteed>>::{closure#0}, core[678332cb0ee15b78]::result::Result<(), rustc_span[9778d555244491c7]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[678332cb0ee15b78]::result::Result<(), rustc_span[9778d555244491c7]::ErrorGuaranteed>>::{closure#1} as core[678332cb0ee15b78]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  46:     0x79ade7733d39 - std::sys::pal::unix::thread::Thread::new::thread_start::h1176f996a4a1b888
  47:     0x79ade908f39d - <unknown>
  48:     0x79ade911449c - <unknown>
  49:                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: please make sure that you have updated to the latest nightly

note: rustc 1.84.0-nightly (251dc8ad8 2024-11-15) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [mir_built] building MIR for `assign_twice`
#1 [check_unsafety] unsafety-checking `assign_twice`
end of query stack
error: aborting due to 7 previous errors; 2 warnings emitted

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

@rustbot label +F-if_let_guard

[matthiaskrgr]

This bisects to #127159 cc @Nadrieril

[matthiaskrgr]

smaller

fn main() {
	match () {
		(! | !) if let _ = Some(0) => {}
		_ => {}
	}
}

[Nadrieril]

Smaller and type-correct:

fn foo(x: !) {
	match x {
		(! | !) if false => {}
		_ => {}
	}
}

[Nadrieril]

See also:

• ICE: leaf_candidate.false_edge_start_block.is_some() duplicate match arm #133117
• ICE: None in compiler/rustc_mir_build/src/build/matches/mod.rs with feature(never_patterns) #130779