ICE: typeck: `no index for a field`

[matthiaskrgr]

snippet:

struct TestStruct {,}

fn edge_case_if() {
    let ts = TestStruct {};
    let _b = || { match ts {
        TestStruct{ x: 1, .. } | _ => (),
    }};
}

Version information

rustc 1.81.0-nightly (1ca578e68 2024-06-20)
binary: rustc
commit-hash: 1ca578e68eb715e772fc0c1b9e6ca7c5b122765a
commit-date: 2024-06-20
host: x86_64-unknown-linux-gnu
release: 1.81.0-nightly
LLVM version: 18.1.7

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

Program output

``` error: expected identifier, found `,` --> /tmp/icemaker_global_tempdir.hJLG4Uu9QCDq/rustc_testrunner_tmpdir_reporting.cVa4rm3LGIDH/mvce.rs:1:20 | 1 | struct TestStruct {,} | ---------- ^ expected identifier | | | while parsing this struct error[E0601]: `main` function not found in crate `mvce` --> /tmp/icemaker_global_tempdir.hJLG4Uu9QCDq/rustc_testrunner_tmpdir_reporting.cVa4rm3LGIDH/mvce.rs:8:2 | 8 | } | ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.hJLG4Uu9QCDq/rustc_testrunner_tmpdir_reporting.cVa4rm3LGIDH/mvce.rs` thread 'rustc' panicked at compiler/rustc_hir_typeck/src/expr_use_visitor.rs:1697:26: no index for a field stack backtrace: 0: 0x71e31da31915 - std::backtrace_rs::backtrace::libunwind::trace::h796e75e96c439f3e at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/../../backtrace/src/backtrace/libunwind.rs:116:5 1: 0x71e31da31915 - std::backtrace_rs::backtrace::trace_unsynchronized::h57b5b13bb46e11ba at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5 2: 0x71e31da31915 - std::sys::backtrace::_print_fmt::h11ce45f986076e87 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/sys/backtrace.rs:68:5 3: 0x71e31da31915 - ::fmt::hcd09ba6a4fc236f1 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/sys/backtrace.rs:44:22 4: 0x71e31da824bb - core::fmt::rt::Argument::fmt::h914f09f4a1c58d59 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/core/src/fmt/rt.rs:165:63 5: 0x71e31da824bb - core::fmt::write::hc590b91d463e6a2c at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/core/src/fmt/mod.rs:1168:21 6: 0x71e31da265af - std::io::Write::write_fmt::hc69b1d0ded026622 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/io/mod.rs:1835:15 7: 0x71e31da316ee - std::sys::backtrace::_print::hc852e4497da27a95 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/sys/backtrace.rs:47:5 8: 0x71e31da316ee - std::sys::backtrace::print::hc624de700d5fe576 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/sys/backtrace.rs:34:9 9: 0x71e31da34129 - std::panicking::default_hook::{{closure}}::hf8d8481f1d9702fb 10: 0x71e31da33ecc - std::panicking::default_hook::he469b58de751f8ee at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/panicking.rs:292:9 11: 0x71e31a147870 - std[eca1b30e63fdea7a]::panicking::update_hook::>::{closure#0} 12: 0x71e31da34a4f - as core::ops::function::Fn>::call::h7fb9108d23a6d563 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/alloc/src/boxed.rs:2076:9 13: 0x71e31da34a4f - std::panicking::rust_panic_with_hook::h738066c73a52890f at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/panicking.rs:804:13 14: 0x71e31da34677 - std::panicking::begin_panic_handler::{{closure}}::h8534a2aac695431b at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/panicking.rs:670:13 15: 0x71e31da31dd9 - std::sys::backtrace::__rust_end_short_backtrace::h3420ee35d28bf807 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/sys/backtrace.rs:171:18 16: 0x71e31da34304 - rust_begin_unwind at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/panicking.rs:661:5 17: 0x71e31da7ea73 - core::panicking::panic_fmt::h51cb44e3a97167f8 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/core/src/panicking.rs:74:14 18: 0x71e31da7e8cb - core::panicking::panic_display::h01c80b100e2db3b0 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/core/src/panicking.rs:264:5 19: 0x71e31da7e8cb - core::option::expect_failed::h227980ecada19c49 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/core/src/option.rs:2023:5 20: 0x71e31c05cd08 - >::cat_pattern::<>::maybe_read_scrutinee, >::walk_expr::{closure#1}>>::{closure#0}> 21: 0x71e31c05c919 - >::cat_pattern::<>::maybe_read_scrutinee, >::walk_expr::{closure#1}>>::{closure#0}> 22: 0x71e31c0669c0 - >::walk_expr 23: 0x71e31c0656b0 - >::consume_expr 24: 0x71e31c06404e - >::walk_block 25: 0x71e31c0656b0 - >::consume_expr 26: 0x71e31c05e887 - ::analyze_closure 27: 0x71e31900c688 - ::visit_expr 28: 0x71e31b8a58ef - ::visit_block 29: 0x71e31b8a780b - rustc_hir_typeck[3a3cc19eb2dfac16]::typeck 30: 0x71e31b8a6ffb - rustc_query_impl[da2d3b64247f93f0]::plumbing::__rust_begin_short_backtrace::> 31: 0x71e31ba031ee - rustc_query_system[5e65d9b3abdd3162]::query::plumbing::try_execute_query::>, false, false, false>, rustc_query_impl[da2d3b64247f93f0]::plumbing::QueryCtxt, false> 32: 0x71e31ba01cdf - rustc_query_impl[da2d3b64247f93f0]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace 33: 0x71e31ba01915 - ::par_body_owners::::{closure#0} 34: 0x71e31ba003bc - rustc_hir_analysis[74e881c9b9f2b37]::check_crate 35: 0x71e31bdf4f87 - rustc_interface[7fb7dc76513cf959]::passes::analysis 36: 0x71e31bdf4ac7 - rustc_query_impl[da2d3b64247f93f0]::plumbing::__rust_begin_short_backtrace::> 37: 0x71e31c433ea5 - rustc_query_system[5e65d9b3abdd3162]::query::plumbing::try_execute_query::>, false, false, false>, rustc_query_impl[da2d3b64247f93f0]::plumbing::QueryCtxt, false> 38: 0x71e31c433c0f - rustc_query_impl[da2d3b64247f93f0]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace 39: 0x71e31c2dd252 - rustc_interface[7fb7dc76513cf959]::interface::run_compiler::, rustc_driver_impl[93e75e0175b92285]::run_compiler::{closure#0}>::{closure#1} 40: 0x71e31c29dac9 - std[eca1b30e63fdea7a]::sys::backtrace::__rust_begin_short_backtrace::, rustc_driver_impl[93e75e0175b92285]::run_compiler::{closure#0}>::{closure#1}, core[daaba097f859fa28]::result::Result<(), rustc_span[1efc0ab8e6bb0790]::ErrorGuaranteed>>::{closure#0}, core[daaba097f859fa28]::result::Result<(), rustc_span[1efc0ab8e6bb0790]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[daaba097f859fa28]::result::Result<(), rustc_span[1efc0ab8e6bb0790]::ErrorGuaranteed>> 41: 0x71e31c29d880 - <::spawn_unchecked_, rustc_driver_impl[93e75e0175b92285]::run_compiler::{closure#0}>::{closure#1}, core[daaba097f859fa28]::result::Result<(), rustc_span[1efc0ab8e6bb0790]::ErrorGuaranteed>>::{closure#0}, core[daaba097f859fa28]::result::Result<(), rustc_span[1efc0ab8e6bb0790]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[daaba097f859fa28]::result::Result<(), rustc_span[1efc0ab8e6bb0790]::ErrorGuaranteed>>::{closure#2} as core[daaba097f859fa28]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0} 42: 0x71e31da3e8cb - as core::ops::function::FnOnce>::call_once::ha1ad2417ff4e2c89 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/alloc/src/boxed.rs:2062:9 43: 0x71e31da3e8cb - as core::ops::function::FnOnce>::call_once::ha5ab2243447620ef at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/alloc/src/boxed.rs:2062:9 44: 0x71e31da3e8cb - std::sys::pal::unix::thread::Thread::new::thread_start::he00df2d38aeed7a5 at /rustc/1ca578e68eb715e772fc0c1b9e6ca7c5b122765a/library/std/src/sys/pal/unix/thread.rs:108:17 45: 0x71e316ca6ded - 46: 0x71e316d2a0dc - 47: 0x0 - 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 1.81.0-nightly (1ca578e68 2024-06-20) running on x86_64-unknown-linux-gnu query stack during panic: #0 [typeck] type-checking `edge_case_if` #1 [analysis] running analysis passes on this crate end of query stack error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0601`. ```

[matthiaskrgr]

126320 cc @oli-obk :D

[oli-obk]

wtf. why does that wrong comma cause the struct to be different from a struct with no fields

[matthiaskrgr]

minimized

struct X {,}

fn main() {
    || {
        if let X { x: 1,} = (X {}) {}
    };
}

[chenyukang]

wtf. why does that wrong comma cause the struct to be different from a struct with no fields

An extra , is a recovered struct variant, and it is skipped here: https://github.com/rust-lang/rust/blob/382148d9a21ae0b506adf44fc1e55a410acde828/compiler/rustc_hir_typeck/src/pat.rs#L1533

so we didn't emit the error like an empty struct: https://github.com/rust-lang/rust/blob/382148d9a21ae0b506adf44fc1e55a410acde828/compiler/rustc_hir_typeck/src/pat.rs#L1610

error[E0026]: struct `X` does not have a field named `x`
 --> src/main.rs:5:20
  |
5 |         if let X { x: 1,} = (X {}) {}
  |                    ^ struct `X` does not have this field

So the compiler continues until the ICE point.

I think a trivial fix will be ok here?

[oli-obk]

Hmm... I'd look into reporting that error even for recovered structs and figuring out how to avoid it just for the cases that this skip was intended to avoid

[chenyukang]

seems there is nothing else we are trying to avoid:

https://github.com/rust-lang/rust/commit/2ea2bb430665277ccb01e514011782b329f78840

I'd prefer not to report the no-field error, since the first error in parsing will point out the root cause, and there is a case like https://github.com/rust-lang/rust/issues/126344, which may introduce noise when there are too many type errors, it's also applied to this issue.

[oli-obk]

Oh... we can probably just replace the is_recovered method with a new tainted_by_errors method and return an Result<(), ErrorGuaranteed>. This way we act as if we reported an error, and thus not continue to the ICE

[oli-obk]

Since we cannot encode an ErrorGuaranteed in the flags list, either take a TyCtxt argument on the tainted_by_errors method, or check if replacing the field field with Result<IndexVec<FieldIdx, FieldDef>, ErrorGuaranteed> works out nicely