Clippy panics on UTF-8 (Chinese) comments in protobuf-generated Rust code

[EMOAIRX]

Summary

Clippy panics with a "byte index is not a char boundary" error when running on Rust code generated from .proto files that contain Chinese (UTF-8) comments. The panic occurs during linting, making it impossible to use clippy on projects with such generated code. Removing the Chinese comments resolves the issue.

Reproducer

To Reproduce Steps to reproduce the behavior:

1. Create a .proto file with Chinese comments, e.g.:

// 发送启动信号
rpc SendStartSignal(StartSignalRequest) returns (StartSignalResponse);

2. Use tonic_build or prost_build to generate Rust code from the proto.
3. Run cargo clippy on the project.
   Expected behavior Clippy should not panic, even if the generated Rust code contains UTF-8 doc comments.

Actual behavior Clippy panics with:

thread 'rustc' panicked at compiler/rustc_resolve/src/rustdoc.rs:573:52:
byte index X is not a char boundary; it is inside '发' (bytes Y..Z) of `/// 发送启动信号`

Version

clippy version: (e.g. clippy 0.1.89 (45f256d9d 2025-05-27))
rustc version: (e.g. rustc 1.89.0-nightly (45f256d9d 2025-05-27))
OS: macOS (Apple Silicon)

Additional Labels

Removing the Chinese comments from the proto file or disabling doc generation avoids the panic.
This only happens with non-ASCII (e.g. Chinese) comments.

[ComputerDruid]

I was able to reproduce this, I added:

diff --git a/examples/proto/echo/echo.proto b/examples/proto/echo/echo.proto
index 49adc34..50f60b1 100644
--- a/examples/proto/echo/echo.proto
+++ b/examples/proto/echo/echo.proto
@@ -32,7 +32,7 @@
 
  // Echo is the echo service.
  service Echo {
-   // UnaryEcho is unary echo.
+   // 发送启动信号
    rpc UnaryEcho(EchoRequest) returns (EchoResponse) {}
    // ServerStreamingEcho is server side streaming.
    rpc ServerStreamingEcho(EchoRequest) returns (stream EchoResponse) {}

on the examples in https://github.com/hyperium/tonic/tree/master/examples , then

❯ rustup override set nightly-2025-05-28
❯ cargo clippy --package examples --bin streaming-client
    Checking examples v0.0.0 (/tmp/tonic/examples)

thread 'rustc' panicked at compiler/rustc_resolve/src/rustdoc.rs:573:52:
byte index 5 is not a char boundary; it is inside '发' (bytes 4..7) of `/// 发送启动信号`
stack backtrace:
   0:     0x7fca2898f533 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::ha3422b3d97a2afe5
   1:     0x7fca29005877 - core::fmt::write::h172d9004d7176029
   2:     0x7fca2a0b8651 - std::io::Write::write_fmt::he69c96b90ad625f2
   3:     0x7fca2898f392 - std::sys::backtrace::BacktraceLock::print::h55fe3d663e8dcf4a
   4:     0x7fca28992f8a - std::panicking::default_hook::{{closure}}::h7798b6fe123749da
   5:     0x7fca28992b0f - std::panicking::default_hook::h7168cef44723d9fb
   6:     0x7fca279b6aa3 - std[afd1485af05e62a]::panicking::update_hook::<alloc[8996f9fee9975b35]::boxed::Box<rustc_driver_impl[2c1a80e926d84f5e]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7fca28993803 - std::panicking::rust_panic_with_hook::h219931f4422da4eb
   8:     0x7fca289934fa - std::panicking::begin_panic_handler::{{closure}}::h9f8a100b65ab934c
   9:     0x7fca2898f9f9 - std::sys::backtrace::__rust_end_short_backtrace::h94b283aa2f1be656
  10:     0x7fca289931bd - __rustc[c809e5aa77cdda96]::rust_begin_unwind
  11:     0x7fca2528f440 - core::panicking::panic_fmt::h55be3c70c467eb79
  12:     0x7fca2732dfb8 - core::str::slice_error_fail_rt::h48d283c4440924fd
  13:     0x7fca26ed546a - core::str::slice_error_fail::h25bf8e5d07a86b3d
  14:     0x7fca28535fe3 - rustc_resolve[7a588aa8e3e1ed5a]::rustdoc::source_span_for_markdown_range
  15:     0x55e5bcb470ae - clippy_lints[a5a5aef6244f56c5]::doc::check_doc::<pulldown_cmark[fe4293ba627e6346]::parse::OffsetIter<&mut clippy_lints[a5a5aef6244f56c5]::doc::check_attrs::fake_broken_link_callback>>
  16:     0x55e5bcb44c08 - <clippy_lints[a5a5aef6244f56c5]::doc::Documentation as rustc_lint[ce376ed602e3bf75]::passes::LateLintPass>::check_attributes
  17:     0x7fca27f1f66f - <rustc_lint[ce376ed602e3bf75]::late::LateContextAndPass<rustc_lint[ce376ed602e3bf75]::late::RuntimeCombinedLateLintPass> as rustc_hir[f0af3f241176fb01]::intravisit::Visitor>::visit_nested_item
  18:     0x7fca27f1f128 - <rustc_lint[ce376ed602e3bf75]::late::LateContextAndPass<rustc_lint[ce376ed602e3bf75]::late::RuntimeCombinedLateLintPass> as rustc_hir[f0af3f241176fb01]::intravisit::Visitor>::visit_nested_item
  19:     0x7fca27f1f128 - <rustc_lint[ce376ed602e3bf75]::late::LateContextAndPass<rustc_lint[ce376ed602e3bf75]::late::RuntimeCombinedLateLintPass> as rustc_hir[f0af3f241176fb01]::intravisit::Visitor>::visit_nested_item
  20:     0x7fca29f3b2de - rustc_lint[ce376ed602e3bf75]::late::check_crate::{closure#0}
  21:     0x7fca29f3b589 - rustc_lint[ce376ed602e3bf75]::late::check_crate
  22:     0x7fca29f3eedf - rustc_interface[4146119d3f353038]::passes::analysis
  23:     0x7fca29f3ecb5 - rustc_query_impl[2be678b5186677a0]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[2be678b5186677a0]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[fd64a7f8ce0ec918]::query::erase::Erased<[u8; 0usize]>>
  24:     0x7fca2a2c3784 - rustc_query_system[2d96945f7a7d8210]::query::plumbing::try_execute_query::<rustc_query_impl[2be678b5186677a0]::DynamicConfig<rustc_query_system[2d96945f7a7d8210]::query::caches::SingleCache<rustc_middle[fd64a7f8ce0ec918]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[2be678b5186677a0]::plumbing::QueryCtxt, true>
  25:     0x7fca2a2c30a8 - rustc_query_impl[2be678b5186677a0]::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
  26:     0x7fca2a1a9647 - rustc_interface[4146119d3f353038]::passes::create_and_enter_global_ctxt::<core[ea5d9ca38f544a92]::option::Option<rustc_interface[4146119d3f353038]::queries::Linker>, rustc_driver_impl[2c1a80e926d84f5e]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  27:     0x7fca2a0c9c8f - rustc_interface[4146119d3f353038]::interface::run_compiler::<(), rustc_driver_impl[2c1a80e926d84f5e]::run_compiler::{closure#0}>::{closure#1}
  28:     0x7fca2a0b2a46 - std[afd1485af05e62a]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[4146119d3f353038]::util::run_in_thread_with_globals<rustc_interface[4146119d3f353038]::util::run_in_thread_pool_with_globals<rustc_interface[4146119d3f353038]::interface::run_compiler<(), rustc_driver_impl[2c1a80e926d84f5e]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  29:     0x7fca2a0b26eb - <<std[afd1485af05e62a]::thread::Builder>::spawn_unchecked_<rustc_interface[4146119d3f353038]::util::run_in_thread_with_globals<rustc_interface[4146119d3f353038]::util::run_in_thread_pool_with_globals<rustc_interface[4146119d3f353038]::interface::run_compiler<(), rustc_driver_impl[2c1a80e926d84f5e]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[ea5d9ca38f544a92]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  30:     0x7fca2a0b3a3d - std::sys::pal::unix::thread::Thread::new::thread_start::h06cdc07e33bef493
  31:     0x7fca23e78850 - <unknown>
  32:     0x7fca23ef77ec - <unknown>
  33:                0x0 - <unknown>

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

note: we would appreciate a bug report: https://github.com/rust-lang/rust-clippy/issues/new?template=ice.yml

note: please make sure that you have updated to the latest nightly

note: please attach the file at `/tmp/tonic/rustc-ice-2025-06-28T01_53_56-396633.txt` to your bug report

note: compiler flags: --crate-type bin -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED]

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

query stack during panic:
#0 [analysis] running analysis passes on this crate
end of query stack
note: Clippy version: clippy 0.1.89 (45f256d9d7 2025-05-27)

error: could not compile `examples` (bin "streaming-client")

Caused by:
  process didn't exit successfully: `/home/cdruid/.rustup/toolchains/nightly-2025-05-28-x86_64-unknown-linux-gnu/bin/clippy-driver /home/cdruid/.rustup/toolchains/nightly-2025-05-28-x86_64-unknown-linux-gnu/bin/rustc --crate-name streaming_client --edition=2021 examples/src/streaming/client.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=211 --crate-type bin --emit=dep-info,metadata -C embed-bitcode=no -C debuginfo=2 --cfg 'feature="autoreload"' --cfg 'feature="cancellation"' --cfg 'feature="compression"' --cfg 'feature="default"' --cfg 'feature="full"' --cfg 'feature="gcp"' --cfg 'feature="grpc-web"' --cfg 'feature="h2c"' --cfg 'feature="health"' --cfg 'feature="json-codec"' --cfg 'feature="mock"' --cfg 'feature="reflection"' --cfg 'feature="routeguide"' --cfg 'feature="streaming"' --cfg 'feature="tls"' --cfg 'feature="tls-client-auth"' --cfg 'feature="tls-rustls"' --cfg 'feature="tower"' --cfg 'feature="tracing"' --cfg 'feature="types"' --cfg 'feature="uds"' --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values("autoreload", "cancellation", "compression", "default", "full", "gcp", "grpc-web", "h2c", "health", "json-codec", "mock", "reflection", "routeguide", "streaming", "tls", "tls-client-auth", "tls-rustls", "tower", "tracing", "types", "uds"))' -C metadata=295842889007bac5 -C extra-filename=-8c3a06e6bf99f218 --out-dir /tmp/tonic/target/debug/deps -C incremental=/tmp/tonic/target/debug/incremental -L dependency=/tmp/tonic/target/debug/deps --extern async_stream=/tmp/tonic/target/debug/deps/libasync_stream-107ba00d8322e5d7.rmeta --extern bytes=/tmp/tonic/target/debug/deps/libbytes-9d3487932bdbd853.rmeta --extern h2=/tmp/tonic/target/debug/deps/libh2-a9960526e0d3da96.rmeta --extern http=/tmp/tonic/target/debug/deps/libhttp-1011bad67192e6a8.rmeta --extern hyper=/tmp/tonic/target/debug/deps/libhyper-fd6314f69a54580d.rmeta --extern hyper_rustls=/tmp/tonic/target/debug/deps/libhyper_rustls-74c8509e20061c86.rmeta --extern hyper_util=/tmp/tonic/target/debug/deps/libhyper_util-0f5a50a35af97f9f.rmeta --extern listenfd=/tmp/tonic/target/debug/deps/liblistenfd-4ea802f03c0d0746.rmeta --extern prost=/tmp/tonic/target/debug/deps/libprost-23cd161beb28f152.rmeta --extern prost_types=/tmp/tonic/target/debug/deps/libprost_types-bc112016c12f8d54.rmeta --extern rand=/tmp/tonic/target/debug/deps/librand-fe1019ca42ce006b.rmeta --extern serde=/tmp/tonic/target/debug/deps/libserde-92a3c1944163f7fc.rmeta --extern serde_json=/tmp/tonic/target/debug/deps/libserde_json-5cced26cc96eb821.rmeta --extern tokio=/tmp/tonic/target/debug/deps/libtokio-1025fe819f886ada.rmeta --extern tokio_rustls=/tmp/tonic/target/debug/deps/libtokio_rustls-929f698d59e64ac1.rmeta --extern tokio_stream=/tmp/tonic/target/debug/deps/libtokio_stream-63fcba2fe196885b.rmeta --extern tokio_util=/tmp/tonic/target/debug/deps/libtokio_util-794192760bfed152.rmeta --extern tonic=/tmp/tonic/target/debug/deps/libtonic-ff71ce27c3c49ca9.rmeta --extern tonic_health=/tmp/tonic/target/debug/deps/libtonic_health-c45f899af5b98443.rmeta --extern tonic_reflection=/tmp/tonic/target/debug/deps/libtonic_reflection-b33e88cfbf1b9162.rmeta --extern tonic_types=/tmp/tonic/target/debug/deps/libtonic_types-09a0c6d57d55f153.rmeta --extern tonic_web=/tmp/tonic/target/debug/deps/libtonic_web-7bc72e02cb92f0ff.rmeta --extern tower=/tmp/tonic/target/debug/deps/libtower-88941da919d2debe.rmeta --extern tower_http=/tmp/tonic/target/debug/deps/libtower_http-37c865ea3508d400.rmeta --extern tracing=/tmp/tonic/target/debug/deps/libtracing-2be5fc652bf93af0.rmeta --extern tracing_subscriber=/tmp/tonic/target/debug/deps/libtracing_subscriber-5666aec8899761c0.rmeta -L native=/tmp/tonic/target/debug/build/ring-d697d01fa1effb9d/out` (exit status: 101)

On the other hand, I wasn't able to reproduce it on latest nightly:

❯ clippy-driver -Vv
rustc 1.90.0-nightly (b03b3a7ec 2025-06-26)
binary: rustc
commit-hash: b03b3a7ec92682be2917540b679478d41c95a30c
commit-date: 2025-06-26
host: x86_64-unknown-linux-gnu
release: 1.90.0-nightly
LLVM version: 20.1.7

Is it possible that it has been fixed already?

[ComputerDruid]

Probable fix: rust-lang/rust#141666