ICE: mir_borrowck encountered mutable promoted

[cramertj]

Error:

error: internal compiler error: librustc_mir/borrow_check/mod.rs:1868: encountered mutable promoted

thread 'main' panicked at 'Box<Any>', librustc_errors/lib.rs:580:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
   1: std::sys_common::backtrace::print
   2: std::panicking::default_hook::{{closure}}
   3: std::panicking::default_hook
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::bug
   8: rustc::session::opt_span_bug_fmt::{{closure}}
   9: rustc::ty::context::tls::with_opt::{{closure}}
  10: rustc::ty::context::tls::with_context_opt
  11: rustc::ty::context::tls::with_opt
  12: rustc::session::opt_span_bug_fmt
  13: rustc::session::bug_fmt
  14: rustc_mir::borrow_check::MirBorrowckCtxt::is_mutable
  15: rustc_mir::borrow_check::MirBorrowckCtxt::access_place
  16: <rustc_mir::borrow_check::MirBorrowckCtxt<'cx, 'gcx, 'tcx> as rustc_mir::dataflow::DataflowResultsConsumer<'cx, 'tcx>>::visit_statement_entry
  17: rustc_mir::borrow_check::do_mir_borrowck
  18: rustc::ty::context::tls::with_related_context
  19: rustc::infer::InferCtxtBuilder::enter
  20: rustc_mir::borrow_check::mir_borrowck
  21: rustc::ty::query::__query_compute::mir_borrowck
  22: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::mir_borrowck<'tcx>>::compute
  23: rustc::dep_graph::graph::DepGraph::with_task_impl
  24: rustc::ty::context::tls::with_related_context
  25: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  26: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  27: rustc::ty::query::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::mir_borrowck
  28: rustc::ty::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::par_body_owners
  29: rustc::util::common::time
  30: rustc::ty::context::tls::enter_context
  31: <std::thread::local::LocalKey<T>>::with
  32: rustc::ty::context::TyCtxt::create_and_enter
  33: rustc_driver::driver::compile_input
  34: rustc_driver::run_compiler_with_pool
  35: <scoped_tls::ScopedKey<T>>::set
  36: <scoped_tls::ScopedKey<T>>::set
  37: syntax::with_globals
  38: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  39: __rust_maybe_catch_panic
  40: rustc_driver::run
  41: rustc_driver::main
  42: std::rt::lang_start::{{closure}}
  43: std::panicking::try::do_call
  44: __rust_maybe_catch_panic
  45: std::rt::lang_start_internal
  46: main
  47: __libc_start_main
  48: _start
query stack during panic:
#0 [mir_borrowck] processing `wire::util::buffer::tests::test_buffer_and_range_slice`
end of query stack
error: aborting due to previous error

For more information about this error, try `rustc --explain E0170`.

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.29.0-dev running on x86_64-unknown-linux-gnu

note: compiler flags: -C linker=/usr/local/google/home/cramertj/src/fuchsia/buildtools/linux-x64/clang/bin/clang -C link-arg=--target=x86_64-unknown-fuchsia -C link-arg=--sysroot=/usr/local/google/home/cramertj/src/fuchsia/out/release-x64/sdks/zircon_sysroot/arch/x64/sysroot -C opt-level=z -C lto=thin --crate-type bin


[5390/6330] ACTION //garnet/public/lib/fidl/rust/fidl:fidl_build(//build/toolchain/fuchsia:x64)
ninja: build stopped: subcommand failed.

This only happens after #52597 cc @oli-obk. The code that triggered this is here.

[oli-obk]

cc @nagisa seems like https://github.com/rust-lang/rust/pull/52597/files#diff-5b4d01d26caf43976125ba0f877e78c0R1856 we need to report an error instead of panicking as originally written

[oli-obk]

Oh it's probably because we do promote &mut []

[oli-obk]

created a fix in #52673, but I have no minimal repro and no time today

[cramertj]

To clarify: you're making this an error? I don't see why we can't allow &mut [] to be promoted.

[oli-obk]

good point

[kennytm]

This ICE is currently causing errors in the style-servo, regex and crates.io crates in https://perf.rust-lang.org/status.html.

[oli-obk]

I have tried building regex 0.1.80 and it does not reproduce the issue for me on master or nightly 😕

trying a stage2 build now

still can't repro on regex, but can repro on OPs file now.

#![feature(nll)]
fn main() {
    let y: &'static mut [u8; 0] = &mut [];
}

[oli-obk]

ok, fix exists now

[Mark-Simulacrum]

It looks like we've fixed the ICE here but there's still a change in behavior here, as well as a faulty diagnostic; this is while compiling cargo-registry from crates.io (at least the version in rustc-perf).

error[E0499]: cannot borrow `promoted` as mutable more than once at a time
  --> src/util/io_util.rs:45:47
   |
45 |         slice = &mut mem::replace(&mut slice, &mut [])[n..];
   |                                               ^^^^^^^ mutable borrow starts here in previous iteration of loop
   |
note: borrowed value must be valid for the anonymous lifetime #2 defined on the function body at 39:1...
  --> src/util/io_util.rs:39:1
   |
39 | / pub fn read_fill(r: &mut R, mut slice: &mut [u8]) -> io::Result<()> {
40 | |     while !slice.is_empty() {
41 | |         let n = r.read(slice)?;
42 | |         if n == 0 {
...  |
47 | |     Ok(())
48 | | }
   | |_^

error: aborting due to previous error