[Nightly ICE] Deep in proc macro: panicked at 'empty field list in the map'

[jhwgh1968]

Code

It is very finicky to reproduce. This GHE branch is as minimal as I could get without significantly changing the structure of the macro or having other errors cover it up. Apologies for the mess!

Updated 2020-08-04: I got it down to a total of only 130 lines of code. Please review the improved cargo expand output below.

Instructions:

1. Clone the project: git clone -b nightly_ice https://github.com/jhwgh1968/rhai.git
2. cd rhai/codegen
3. RUST_BACKTRACE=1 cargo check --tests

Meta

The ICE was triggered by change in 44600aa2, where I simply changed the scoping on a nested inner struct generated by a macro from public to private.

rustc --version --verbose:

rustc 1.47.0-nightly (6c8927b0c 2020-07-26)
binary: rustc
commit-hash: 6c8927b0cf80ceee19386026cf9d7fd4fd9d486f
commit-date: 2020-07-26
host: x86_64-unknown-linux-gnu
release: 1.47.0-nightly
LLVM version: 10.0

Error output

On stable, errors regarding scoping are printed (this error is repeated many times):

error[E0603]: tuple struct `Token` is private
  --> tests/test_functions.rs:20:5
   |
20 | /     rhai::register_exported_fn!(
21 | |         m,
22 | |         "euclidean_distance".to_string(),
23 | |         raw_fn::distance_function
24 | |     );
   | |______^ private tuple struct
   |
note: the tuple struct `Token` is defined here
  --> tests/test_functions.rs:9:5
   |
9  |     #[export_fn]
   |     ^^^^^^^^^^^^
   = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)

On nightly, a backtrace occurs.

Backtrace

thread 'rustc' panicked at 'empty field list in the map', src/librustc_resolve/diagnostics.rs:1068:50
stack backtrace:
   0:     0x7fc302be4215 - backtrace::backtrace::libunwind::trace::h75aedf5f78e5147f
                               at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
   1:     0x7fc302be4215 - backtrace::backtrace::trace_unsynchronized::h18fb73c9ac9ae753
                               at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
   2:     0x7fc302be4215 - std::sys_common::backtrace::_print_fmt::h65f97470ff13ec84
                               at src/libstd/sys_common/backtrace.rs:78
   3:     0x7fc302be4215 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hee061c54ddc9f024
                               at src/libstd/sys_common/backtrace.rs:59
   4:     0x7fc302c2041c - core::fmt::write::hfbd2baad61ed21a8
                               at src/libcore/fmt/mod.rs:1117
   5:     0x7fc302bd5f52 - std::io::Write::write_fmt::h72f9bd227f40dc62
                               at src/libstd/io/mod.rs:1508
   6:     0x7fc302be90b0 - std::sys_common::backtrace::_print::h2d2cd8fe02feb5fa
                               at src/libstd/sys_common/backtrace.rs:62
   7:     0x7fc302be90b0 - std::sys_common::backtrace::print::h801b12991252ba7c
                               at src/libstd/sys_common/backtrace.rs:49
   8:     0x7fc302be90b0 - std::panicking::default_hook::{{closure}}::h25fc1fbf3b63b5c8
                               at src/libstd/panicking.rs:198
   9:     0x7fc302be8dfc - std::panicking::default_hook::h62c897957a5e0f26
                               at src/libstd/panicking.rs:217
  10:     0x7fc30336f719 - rustc_driver::report_ice::h54e3b417084b44b0
  11:     0x7fc2f87eb936 - <alloc::boxed::Box<F> as core::ops::function::Fn<A>>::call::h9c411e66d4b5afe3
                               at /rustc/6c8927b0cf80ceee19386026cf9d7fd4fd9d486f/src/liballoc/boxed.rs:1088
  12:     0x7fc2f87b8ec5 - proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::enter::{{closure}}::{{closure}}::h967b1f123fdc59e1
                               at /rustc/6c8927b0cf80ceee19386026cf9d7fd4fd9d486f/src/libproc_macro/bridge/client.rs:318
  13:     0x7fc302be9828 - std::panicking::rust_panic_with_hook::hb8a276f163c59810
                               at src/libstd/panicking.rs:530
  14:     0x7fc302be93fb - rust_begin_unwind
                               at src/libstd/panicking.rs:437
  15:     0x7fc302c1cfc1 - core::panicking::panic_fmt::h9cc57011b345cfad
                               at src/libcore/panicking.rs:85
  16:     0x7fc302c1cba3 - core::option::expect_failed::hf0849e257b6323a4
                               at src/libcore/option.rs:1265
  17:     0x7fc3041229b9 - rustc_resolve::Resolver::resolve_crate::h9141d40acb3e873e
  18:     0x7fc30350bc0d - rustc_interface::passes::configure_and_expand_inner::h99f6e5687869f977
  19:     0x7fc303576b99 - rustc_interface::passes::configure_and_expand::{{closure}}::ha0a6222929510b34
  20:     0x7fc303561450 - rustc_data_structures::box_region::PinnedGenerator<I,A,R>::new::h6510d01dfe55aa38
  21:     0x7fc30350a881 - rustc_interface::passes::configure_and_expand::h266ae77065114d38
  22:     0x7fc303523514 - rustc_interface::queries::Queries::expansion::h02073762737d1d86
  23:     0x7fc30332a303 - rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter::h3b5436b320054acc
  24:     0x7fc3033c9277 - rustc_span::with_source_map::hd3215c6d07150bbc
  25:     0x7fc30332bfb6 - rustc_interface::interface::create_compiler_and_run::hc502b394ead637d1
  26:     0x7fc30335532d - scoped_tls::ScopedKey<T>::set::hb09c39dbfa5a4396
  27:     0x7fc30337b4a2 - std::sys_common::backtrace::__rust_begin_short_backtrace::h4fa4ac8c571754e6
  28:     0x7fc30333826e - core::ops::function::FnOnce::call_once{{vtable.shim}}::h23cc72206c0cf83b
  29:     0x7fc302bf7d3a - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::h3e41d894970cea2f
                               at /rustc/6c8927b0cf80ceee19386026cf9d7fd4fd9d486f/src/liballoc/boxed.rs:1074
  30:     0x7fc302bf7d3a - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::h9a318bb00b7f8871
                               at /rustc/6c8927b0cf80ceee19386026cf9d7fd4fd9d486f/src/liballoc/boxed.rs:1074
  31:     0x7fc302bf7d3a - std::sys::unix::thread::Thread::new::thread_start::hf522342530b04cb6
                               at src/libstd/sys/unix/thread.rs:87
  32:     0x7fc302af9422 - start_thread
  33:     0x7fc302a0fbf3 - __GI___clone
  34:                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 1.47.0-nightly (6c8927b0c 2020-07-26) running on x86_64-unknown-linux-gnu

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

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

query stack during panic:
end of query stack

cargo expand with pub struct (updated 2020-08-04)

#![feature(prelude_import)]
#[prelude_import]
use std::prelude::v1::*;
#[macro_use]
extern crate std;
use rhai::module_resolvers::*;
use rhai::plugin::*;
use rhai::Module;
pub mod raw_fn {
    use rhai::plugin::*;
    use rhai::FLOAT;
    pub fn distance_function(x1: FLOAT, y1: FLOAT, x2: FLOAT, y2: FLOAT) -> FLOAT {
        ((y2 - y1).abs().powf(2.0) + (x2 - x1).abs().powf(2.0)).sqrt()
    }
    #[allow(unused)]
    pub mod rhai_fn__distance_function {
        use super::*;
        pub struct Token();
        impl PluginFunction for Token {
            fn call(
                &self,
                args: &mut [&mut Dynamic],
                pos: Position,
            ) -> Result<Dynamic, Box<EvalAltResult>> {
                Ok(Dynamic::from(distance_function()))
            }
        }
        pub fn Token__callable() -> CallableFunction {
            CallableFunction::from_plugin(Token())
        }
    }
}
extern crate test;
#[cfg(test)]
#[rustc_test_marker]
pub const raw_fn_test: test::TestDescAndFn = test::TestDescAndFn {
    desc: test::TestDesc {
        name: test::StaticTestName("raw_fn_test"),
        ignore: false,
        allow_fail: false,
        should_panic: test::ShouldPanic::No,
        test_type: test::TestType::IntegrationTest,
    },
    testfn: test::StaticTestFn(|| test::assert_test_result(raw_fn_test())),
};
fn raw_fn_test() {
    let mut m = Module::new();
    m.set_fn(
        "euclidean_distance".to_string(),
        rhai::FnAccess::Public,
        raw_fn::rhai_fn__distance_function::Token()
            .input_types()
            .as_ref(),
    );
}
#[main]
pub fn main() -> () {
    extern crate test;
    test::test_main_static(&[&raw_fn_test])
}

[jhwgh1968]

I have reduced this reproducer from about 500 lines of code total to 130 lines total. There are more syntax errors in it now, but the panic still triggers before them.

Most of the other things I could change create an error that short circuits the compiler before the panic could trigger.

EDIT: I also just updated the backtrace, because I didn't ask for a full backtrace last time.

[JohnTitor]

Let's get a MCVE and bisect the culprit PR.
@rustbot ping cleanup

[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 @imtsuki @kanru @KarlK90 @LeSeulArtichaut @MAdrianMattocks @matheus-consoli @mental32 @nmccarty @Noah-Kennedy @pard68 @PeytonT @pierreN @Redblueflame @RobbieClarken @RobertoSnap @robjtede @SarthakSingh31 @senden9 @shekohex @sinato @spastorino @turboladen @woshilapin @yerke

[Aaron1011]

Minimized:

mod foo {
    struct Bar();
}

fn main() {
    foo::Bar();
}

[petrochenkov]

#74211 is the likely cause.