Compiler started panicking on build, reverting changes does not stop crashes

[ZacBlanco]

Sorry, I don't have much experience with the Rust compiler yet -- would love to learn more :)

I was working on a project for a class doing some system benchmarking on nightly Rust. Everything was working and after a set of changes I started getting compiler crashes. Still trying to work out exactly what change triggered the crashes. I reverted a bunch of code to a state where I knew it compiled previously but it still crashed. I'm unsure if it's related to my code or not. I've attached a zip with the Cargo.toml and the main.rsfile.

Since reverting changes does not seem to affect the build, could this be an issue with already-compiled artifacts under ./target?

Code

I don't have the time right now to provide a strictly minimal example -- I could not reproduce this either. The two files in there are the only artifacts in the project.

code.tar.gz
See attached code.tar.gz

Meta

rustc --version --verbose:

zac@hulk:~/projects/cse221$ rustc --version --verbose
rustc 1.50.0-nightly (3d6705aa5 2020-12-07)
binary: rustc
commit-hash: 3d6705aa5abffe94c83bf09af8c3ba3c599845fc
commit-date: 2020-12-07
host: x86_64-unknown-linux-gnu
release: 1.50.0-nightly

Error output

zac@hulk:~/projects/cse221$ RUST_BACKTRACE=1 cargo build
   Compiling cse221 v0.1.0 (/home/zac/projects/cse221)
warning: constant is never used: `GB`
   --> src/main.rs:817:1
    |
817 | const GB: usize = 1024 * MB;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(dead_code)]` on by default

warning: function is never used: `drop_caches`
    --> src/main.rs:1041:4
     |
1041 | fn drop_caches() -> Result<(), Err> {
     |    ^^^^^^^^^^^

warning: function is never used: `measure_buffer_cache`
    --> src/main.rs:1056:4
     |
1056 | fn measure_buffer_cache() -> Result<(), Err> {
     |    ^^^^^^^^^^^^^^^^^^^^

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 bin

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

query stack during panic:
end of query stack
warning: 3 warnings emitted

error: could not compile `cse221`

To learn more, run the command again with --verbose.

backtrace

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.

[ZacBlanco]

A brief update:
I saved the state under the ./target directory somewhere else in case it could be useful, and then tried compiling again with a fresh build directory. With a fresh directory, everything worked fine.

Based on this, I would suspect that somehow some compiled files in the build directory were corrupted? The compressed directory is ~155M. If someone thinks the state of the build directory would be useful to try to reproduce this I can upload it somewhere.

[ghost]

I think this is #79661.
By the way, I'm just a normal Rust user reporting a bug here, but even I noticed that #79661 is duplicated many times.

[LeSeulArtichaut]

Closing as duplicate of #79661. Thanks for the bug report!