slice index starts at 5 but ends at 4

[sanpii]

Code

This error appears when I add a new line in a macro with a unknown type:

"subcommand" => subcommand::Builder,

This is expanded as:

subcommands.insert("subcommand", <subcommand::Builder as crate::command::Builder>::new("subcommand") as Box<dyn crate::command::Builder>);

The rust-analyzer error:

Cannot find type `Builder` in module `subcommand` not found in `subcommand`.

I made this many times (it’s a early stage development software), but this new one (~270nth) this error appears.

Meta

rustc --version --verbose:

rustc 1.89.0 (29483883e 2025-08-04)
binary: rustc
commit-hash: 29483883eed69d5fb4db01964cdf2af4d86e9cb2
commit-date: 2025-08-04
host: x86_64-unknown-linux-gnu
release: 1.89.0
LLVM version: 20.1.7

This bug also exists in nightly (1.91.0-nightly (7ad23f43a 2025-09-09)) and without cargo configuration file.

Error output

$ RUST_BACKTRACE=1 cargo build
   Compiling postkey v0.1.0 (/home/sanpi/projects/rust/postkey)

thread 'rustc' panicked at /rustc-dev/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/alloc/src/vec/mod.rs:2678:36:
slice index starts at 5 but ends at 4
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::slice::index::slice_index_order_fail::do_panic::runtime
   3: core::slice::index::slice_index_order_fail
   4: <rustc_errors::styled_buffer::StyledBuffer>::replace
   5: <rustc_errors::emitter::HumanEmitter>::emit_messages_default_inner::{closure#0}
   6: <rustc_errors::emitter::HumanEmitter as rustc_errors::emitter::Emitter>::emit_diagnostic
   7: <rustc_errors::json::Diagnostic>::from_errors_diagnostic
   8: <rustc_errors::json::JsonEmitter as rustc_errors::emitter::Emitter>::emit_diagnostic
   9: <rustc_errors::DiagCtxtInner>::emit_diagnostic::{closure#3}
  10: rustc_interface::callbacks::track_diagnostic::<core::option::Option<rustc_span::ErrorGuaranteed>>::{closure#0}
  11: rustc_interface::callbacks::track_diagnostic::<core::option::Option<rustc_span::ErrorGuaranteed>>
  12: <rustc_errors::DiagCtxtInner>::emit_diagnostic
  13: <rustc_errors::DiagCtxtHandle>::emit_diagnostic
  14: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  15: <rustc_resolve::Resolver>::resolve_crate::{closure#0}
  16: <rustc_resolve::Resolver>::resolve_crate
  17: rustc_interface::passes::configure_and_expand
  18: rustc_interface::passes::resolver_for_lowering_raw
      [... omitted 2 frames ...]
  19: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  20: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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: rustc 1.89.0 (29483883e 2025-08-04) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type bin -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED] -C link-arg=-fuse-ld=lld

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

query stack during panic:
#0 [resolver_for_lowering_raw] getting the resolver for lowering
end of query stack
For more information about this error, try `rustc --explain E0412`.
error: could not compile `postkey` (bin "postkey")

Caused by:
  process didn't exit successfully: `/home/sanpi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/rustc --crate-name postkey --edition=2024 src/main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=167 --crate-type bin --emit=dep-info,link -C embed-bitcode=no -C debuginfo=2 --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values())' -C metadata=cbd9df087f182685 -C extra-filename=-37c29d03d7b94f0c --out-dir /home/sanpi/projects/rust/postkey/target/debug/deps -C incremental=/home/sanpi/projects/rust/postkey/target/debug/incremental -L dependency=/home/sanpi/projects/rust/postkey/target/debug/deps --extern derive_more=/home/sanpi/projects/rust/postkey/target/debug/deps/libderive_more-99848350edde0a49.rlib --extern dyn_clone=/home/sanpi/projects/rust/postkey/target/debug/deps/libdyn_clone-e8110d5f11504192.rlib --extern elephantry=/home/sanpi/projects/rust/postkey/target/debug/deps/libelephantry-d92bcff8301c1786.rlib --extern envir=/home/sanpi/projects/rust/postkey/target/debug/deps/libenvir-4e1e0ceeafee9aa3.rlib --extern log=/home/sanpi/projects/rust/postkey/target/debug/deps/liblog-76cf59219504c6cb.rlib --extern thiserror=/home/sanpi/projects/rust/postkey/target/debug/deps/libthiserror-3e46ed291a111f91.rlib -C link-arg=-fuse-ld=lld -L native=/usr/lib` (exit status: 101)

[lolbinarycat]

It would be appreciated if you could provide a complete reproducer, perhaps even minifiying it with treereduce-rust. At the very least, providing a permalink to the repo and commit that cause this crash would allow other people to actually work on this and try to fix it.

[sanpii]

I put a minimal code here: https://github.com/sanpii/rust-issue-146398

I'll try to minifiying it with treereduce.

[heaths]

I'm seeing this on rustc 1.93 and 1.94 as well. rust-analyzer (bundled with VSCode or from ~/.cargo/bin/ - either) is showing some warnings about cyclic dependencies (deps -> devDeps -> deps), but those are nothing new in our workspace. Figured it might be relevant, though.

Because I updated rust I also deleted my target/ directory and rebuilt entirely. In the past I saw some issues with torn state, but that doesn't appear to be the case here. My workspace builds with only a couple of unused lints (expected for now / WIP).

[bb1yd]

Can't reproduce the ICE on rustc 1.96.0 and rustc 1.98.0-nightly (df6ee909e 2026-06-28)

@rustbot label +e-needs-test