ICE: rustdoc on transmute-size-mismatch-before-typeck.rs: size-changing transmute, should have been caught by transmute checking

[matthiaskrgr]

Code

code from ./src/test/ui/consts/transmute-size-mismatch-before-typeck.rs

#![feature(const_transmute)]

// normalize-stderr-64bit "64 bits" -> "word size"
// normalize-stderr-32bit "32 bits" -> "word size"
// normalize-stderr-64bit "128 bits" -> "2 * word size"
// normalize-stderr-32bit "64 bits" -> "2 * word size"

fn main() {
    match &b""[..] {
        ZST => {} //~ ERROR could not evaluate constant pattern
                  //~| ERROR could not evaluate constant pattern
    }
}

const ZST: &[u8] = unsafe { std::mem::transmute(1usize) };
//~^ ERROR any use of this value will cause an error
//~| ERROR cannot transmute between types of different sizes

// Once the `any use of this value will cause an error` disappears in this test, make sure to
// remove the `TransmuteSizeDiff` error variant and make its emitter site an assertion again.

Meta

rustc --version --verbose:

rustdoc 1.50.0-nightly (1c389ffef 2020-11-24)
binary: rustdoc
commit-hash: 1c389ffeff814726dec325f0f2b0c99107df2673
commit-date: 2020-11-24
host: x86_64-unknown-linux-gnu
release: 1.50.0-nightly

Error output

error: internal compiler error: size-changing transmute, should have been caught by transmute checking
  --> ./src/test/ui/consts/transmute-size-mismatch-before-typeck.rs:15:29
   |
15 | const ZST: &[u8] = unsafe { std::mem::transmute(1usize) };
   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: delayed at compiler/rustc_mir/src/interpret/place.rs:922:27

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', compiler/rustc_errors/src/lib.rs:974:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

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-nightly (1c389ffef 2020-11-24) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

Backtrace

error: internal compiler error: size-changing transmute, should have been caught by transmute checking
  --> ./src/test/ui/consts/transmute-size-mismatch-before-typeck.rs:15:29
   |
15 | const ZST: &[u8] = unsafe { std::mem::transmute(1usize) };
   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: delayed at compiler/rustc_mir/src/interpret/place.rs:922:27

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', compiler/rustc_errors/src/lib.rs:974:13
stack backtrace:
   0:     0x7fe3d2942e30 - std::backtrace_rs::backtrace::libunwind::trace::h746c3e9529d524bc
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/../../backtrace/src/backtrace/libunwind.rs:90:5
   1:     0x7fe3d2942e30 - std::backtrace_rs::backtrace::trace_unsynchronized::h86340908ff889faa
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7fe3d2942e30 - std::sys_common::backtrace::_print_fmt::h43f85f9b18230404
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x7fe3d2942e30 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hc132ae1a5b5aa7cd
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:46:22
   4:     0x7fe3d29b5c4c - core::fmt::write::hdf023a0036d2a25f
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/core/src/fmt/mod.rs:1078:17
   5:     0x7fe3d29349a2 - std::io::Write::write_fmt::h8580846154bcb66a
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/io/mod.rs:1519:15
   6:     0x7fe3d2946a95 - std::sys_common::backtrace::_print::h7ee55fed88d107a3
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:49:5
   7:     0x7fe3d2946a95 - std::sys_common::backtrace::print::h54a7d3e52a524177
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:36:9
   8:     0x7fe3d2946a95 - std::panicking::default_hook::{{closure}}::h60921e857bf55a40
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:208:50
   9:     0x7fe3d29465ea - std::panicking::default_hook::hf0f9afb1017317fc
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:225:9
  10:     0x7fe3d31d3bb8 - rustc_driver::report_ice::ha25ae86a5858acc3
  11:     0x7fe3d2947396 - std::panicking::rust_panic_with_hook::h8d66bf42b407aaea
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:595:17
  12:     0x7fe3d2946eb7 - std::panicking::begin_panic_handler::{{closure}}::hde71edcd925d0c5e
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:497:13
  13:     0x7fe3d29432ec - std::sys_common::backtrace::__rust_end_short_backtrace::h8a3c7d6cea578919
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:141:18
  14:     0x7fe3d2946e19 - rust_begin_unwind
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:493:5
  15:     0x7fe3d2946dcb - std::panicking::begin_panic_fmt::hee67ce14b77d0396
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:435:5
  16:     0x7fe3d6336f11 - rustc_errors::HandlerInner::flush_delayed::h336555a5d5079cda
  17:     0x7fe3d63333d1 - <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop::he52694f8b8fafc7c
  18:     0x560c7c2e3226 - core::ptr::drop_in_place::he12f0fc8a3bb0500
  19:     0x560c7c2e72b6 - <alloc::rc::Rc<T> as core::ops::drop::Drop>::drop::hc65b7dbe435be8b6
  20:     0x560c7c268e0c - rustdoc::main_options::h8a5cda9c1c8c625b
  21:     0x560c7c3afa68 - rustc_span::with_session_globals::h7a83fbbd64fb6823
  22:     0x560c7c29630e - std::sys_common::backtrace::__rust_begin_short_backtrace::h50722f4a01515f7b
  23:     0x560c7c3c803a - core::ops::function::FnOnce::call_once{{vtable.shim}}::h22276985fb540191
  24:     0x7fe3d295665a - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hea1090dbdcecbf5a
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/alloc/src/boxed.rs:1318:9
  25:     0x7fe3d295665a - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h8d5723d3912bd325
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/alloc/src/boxed.rs:1318:9
  26:     0x7fe3d295665a - std::sys::unix::thread::Thread::new::thread_start::hc17a425ca2995724
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys/unix/thread.rs:71:17
  27:     0x7fe3d28323e9 - start_thread
  28:     0x7fe3d2618293 - __GI___clone
  29:                0x0 - <unknown>

error: internal compiler error: unexpected panic

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-nightly (1c389ffef 2020-11-24) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

[matthiaskrgr]

@rustbot label -T-compiler +T-rustdoc

[jyn514]

MCVE:

const ZST: &[u8] = unsafe { std::mem::transmute(1usize) };

I expect this is the same sort of issue as #73566 (comment) where rustdoc ignores errors that the compiler requires to be emitted.

Assigning P-low by the same rationale as #79496 (comment).

[chengniansun]

I found a similar duplicate.

pub const ZST: u8 = std::mem::transmute(1usize);

[JohnTitor]

Triage: fixed by #96046, marking as E-needs-test.