rustc nightly hangs with cross-crate trait bound issue involving pub use crate or extern crate self #149092
Description
rustc 1.93.0-nightly (3d461af2a 2025-11-18) hangs without producing any output instead of producing an error about an unsatisfied trait bound. The case involves at least two crates, I haven't been able to reduce it further. Here's a short shell script that sets it up by creating the crates in the current directory:
cargo new --bin user
cargo new --lib library
(cd user && cargo add --path ../library)
cat > user/src/main.rs <<EOF
fn assert_binread<T: library::BinRead>() {}
fn main() {
assert_binread::<()>();
}
EOF
cat > library/src/lib.rs <<EOF
pub trait BinRead {}
pub struct PosValue<T> {
pub t: T,
}
impl<T: BinRead> BinRead for PosValue<T> {}
pub use crate as library;
EOFRunning those commands and then cd user && cargo +nightly check, I observe a hang on:
Building [=============> ] 1/2: user(bin)
Whereas with cargo check on 1.91.1 stable it produces the expected error immediately:
error[E0277]: the trait bound `(): BinRead` is not satisfied
--> src/main.rs:3:22
|
3 | assert_binread::<()>();
| ^^ the trait `BinRead` is not implemented for `()`
|
= help: the trait `BinRead` is implemented for `PosValue<T>`
note: required by a bound in `assert_binread`
--> src/main.rs:1:22
|
1 | fn assert_binread<T: library::BinRead>() {}
| ^^^^^^^^^^^^^^^^ required by this bound in `assert_binread`
I looked at the open I-hang issues and this does not seem to match any of them. I also tried setting RUSTFLAGS=-Znext-solver=globally (as many of them are marked as "fixed-by-next-solver") but the hang still reproduces.
The library crate here was reduced from binrw 0.15.0. It uses extern crate self as binrw similarly to the pub use crate as library here — to hazard a guess, maybe that causes some kind of infinite loop related to name resolution.
Meta
rustc +nightly --version --verbose:
rustc 1.93.0-nightly (3d461af2a 2025-11-18)
binary: rustc
commit-hash: 3d461af2a23456a2676aadb13b4253c87bdfe28d
commit-date: 2025-11-18
host: x86_64-unknown-linux-gnu
release: 1.93.0-nightly
LLVM version: 21.1.5
RUSTFLAGS=-Ztime-passes cargo +nightly check output:
Checking library v0.1.0 (/path/to/library)
time: 0.000; rss: 36MB -> 37MB ( +1MB) parse_crate
time: 0.000; rss: 43MB -> 43MB ( +0MB) crate_injection
time: 0.003; rss: 43MB -> 53MB ( +10MB) expand_crate
time: 0.004; rss: 43MB -> 53MB ( +10MB) macro_expand_crate
time: 0.000; rss: 53MB -> 53MB ( +0MB) AST_validation
time: 0.000; rss: 53MB -> 54MB ( +0MB) finalize_macro_resolutions
time: 0.000; rss: 54MB -> 54MB ( +1MB) late_resolve_crate
time: 0.000; rss: 54MB -> 54MB ( +0MB) resolve_check_unused
time: 0.001; rss: 53MB -> 54MB ( +1MB) resolve_crate
time: 0.000; rss: 54MB -> 55MB ( +0MB) write_dep_info
time: 0.000; rss: 55MB -> 55MB ( +0MB) complete_gated_feature_checking
time: 0.000; rss: 56MB -> 57MB ( +0MB) looking_for_entry_point
time: 0.000; rss: 56MB -> 57MB ( +0MB) misc_checking_1
time: 0.000; rss: 57MB -> 57MB ( +0MB) coherence_checking
time: 0.000; rss: 57MB -> 57MB ( +0MB) type_check_crate
time: 0.000; rss: 58MB -> 58MB ( +0MB) lint_checking
time: 0.002; rss: 57MB -> 58MB ( +1MB) misc_checking_3
time: 0.000; rss: 58MB -> 58MB ( +0MB) generate_crate_metadata
time: 0.000; rss: 58MB -> 59MB ( +1MB) codegen_crate
time: 0.000; rss: 59MB -> 60MB ( +0MB) encode_query_results
time: 0.000; rss: 59MB -> 60MB ( +0MB) incr_comp_serialize_result_cache
time: 0.003; rss: 59MB -> 60MB ( +1MB) incr_comp_persist_result_cache
time: 0.003; rss: 59MB -> 60MB ( +1MB) serialize_dep_graph
time: 0.028; rss: 28MB -> 49MB ( +21MB) total
Checking user v0.1.0 (/path/to/user)
time: 0.000; rss: 36MB -> 37MB ( +1MB) parse_crate
time: 0.000; rss: 43MB -> 43MB ( +0MB) crate_injection
time: 0.003; rss: 43MB -> 53MB ( +10MB) expand_crate
time: 0.003; rss: 43MB -> 53MB ( +10MB) macro_expand_crate
time: 0.000; rss: 53MB -> 53MB ( +0MB) AST_validation
time: 0.000; rss: 53MB -> 53MB ( +0MB) finalize_macro_resolutions
time: 0.000; rss: 53MB -> 54MB ( +0MB) late_resolve_crate
time: 0.000; rss: 54MB -> 54MB ( +0MB) resolve_check_unused
time: 0.001; rss: 53MB -> 54MB ( +1MB) resolve_crate
time: 0.000; rss: 54MB -> 54MB ( +0MB) write_dep_info
time: 0.000; rss: 54MB -> 54MB ( +0MB) complete_gated_feature_checking
time: 0.000; rss: 56MB -> 56MB ( +0MB) looking_for_entry_point
time: 0.001; rss: 56MB -> 57MB ( +1MB) misc_checking_1
time: 0.001; rss: 57MB -> 62MB ( +4MB) coherence_checking
Building [=============> ] 1/2: user(bin)