Description
I encountered the backtrace that you can find below when compiling the documentation for Tokio. Unfortunately I am not able to provide a reproducible example because the panic appears to have been caused by the specific state of the incremental artifacts in the target/ directory when compiling the code.
The error was triggered after having performed a git switch some-other-branch from one version of the code to another. I don't think this checkout has modified any code in the tokio-test crate.
The compiler version in question was rustc 1.50.0-nightly (3d6705aa5 2020-12-07) running on Arch Linux. The error is persisted if I run the command several times, but both upgrading rustc and deleting target/ makes it go away. I assume that upgrading rustc doesn't trigger it because it doesn't try to reuse the old artifacts, which is why I submitted this even though I could not trigger it after upgrading.
Backtrace
tokio $ RUST_BACKTRACE=1 RUSTDOCFLAGS="--cfg docsrs" cargo +nightly doc --all-features
warning: output filename collision.
The lib target `pin-project-lite` in package `pin-project-lite v0.2.0` has the same output filename as the lib target `pin-project-lite` in package `pin-project-lite v0.1.10`.
Colliding filename is: /home/alice/src/tokio/target/doc/pin_project_lite/index.html
The targets should have unique names.
This is a known bug where multiple crates with the same name use
the same path; see <https://github.com/rust-lang/cargo/issues/6313>.
Checking tokio-test v0.4.0 (/home/alice/src/tokio/tokio-test)
Documenting tokio-test v0.4.0 (/home/alice/src/tokio/tokio-test)
Documenting tokio-util v0.6.0 (/home/alice/src/tokio/tokio-util)
Documenting tests-build v0.1.0 (/home/alice/src/tokio/tests-build)
thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', compiler/rustc_middle/src/ty/query/mod.rs:235:5
stack backtrace:
0: rust_begin_unwind
at /rustc/3d6705aa5abffe94c83bf09af8c3ba3c599845fc/library/std/src/panicking.rs:493:5
1: core::panicking::panic_fmt
at /rustc/3d6705aa5abffe94c83bf09af8c3ba3c599845fc/library/core/src/panicking.rs:92:14
2: core::panicking::panic
at /rustc/3d6705aa5abffe94c83bf09af8c3ba3c599845fc/library/core/src/panicking.rs:50:5
3: rustc_middle::ty::query::try_load_from_on_disk_cache
4: rustc_query_system::dep_graph::graph::DepGraph<K>::exec_cache_promotions
5: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
6: rustc_incremental::persist::save::save_in
7: rustc_data_structures::sync::join
8: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
9: rustc_incremental::persist::save::save_dep_graph
10: rustc_codegen_ssa::base::finalize_tcx
11: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
12: rustc_session::utils::<impl rustc_session::session::Session>::time
13: rustc_interface::passes::QueryContext::enter
14: rustc_interface::queries::Queries::ongoing_codegen
15: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
16: rustc_span::with_source_map
17: rustc_interface::interface::create_compiler_and_run
18: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
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 1.50.0-nightly (3d6705aa5 2020-12-07) running on x86_64-unknown-linux-gnu
note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type lib
note: some of the compiler flags provided by cargo are hidden
query stack during panic:
end of query stack
error: could not compile `tokio-test`
I hope that the above panic backtrace is enough that you can figure out what went wrong, because if not, then I'm sorry but I can't reproduce it.