ICE with incr comp

[durka]

I upgraded the chrono dependency from 0.2 to 0.3 in several crates and recompiled. This is what happened:

Alexs-MacBook-Air-3:nri alex$ RUST_BACKTRACE=1 cargo build
   Compiling web v0.1.0 (file:///Users/alex/Documents/research/proton/code/nri/crates/front/web)
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/blob/master/CONTRIBUTING.md#bug-reports

note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', /Users/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-mac/build/src/libcore/option.rs:323
stack backtrace:
   1:        0x1104a95ec - std::sys::imp::backtrace::tracing::imp::write::hf587afb8e94ad165
   2:        0x1104b604e - std::panicking::default_hook::{{closure}}::haf3443cb412055ce
   3:        0x1104b5bf3 - std::panicking::default_hook::h742f925bfab3bbfa
   4:        0x1104b6507 - std::panicking::rust_panic_with_hook::h6f06ff8d28a94df6
   5:        0x1104b63b4 - std::panicking::begin_panic::h7b9167ba3324cfae
   6:        0x1104b62d2 - std::panicking::begin_panic_fmt::hb5f8f1fe0fe23e28
   7:        0x1104b6237 - rust_begin_unwind
   8:        0x1104f3e40 - core::panicking::panic_fmt::he6eb92dab4407c61
   9:        0x1104f3d44 - core::panicking::panic::h16db271caf2c9025
  10:        0x10b9523e1 - rustc_incremental::persist::load::decode_dep_graph::hd9a1e8a507634d7f
  11:        0x10b948c8f - rustc_incremental::persist::load::load_dep_graph::h5f726d61d7f24d69
  12:        0x10b4ae01a - rustc_driver::driver::phase_3_run_analysis_passes::{{closure}}::h46c275184428de94
  13:        0x10b4a15da - rustc_driver::driver::phase_3_run_analysis_passes::h9f46d8470c4871d9
  14:        0x10b490ba0 - rustc_driver::driver::compile_input::h550b23c65a0bc968
  15:        0x10b4d824e - rustc_driver::run_compiler::h65867e99dfb91e54
  16:        0x10b3f00d8 - std::panicking::try::do_call::hdfa57184047b194c
  17:        0x1104b911a - __rust_maybe_catch_panic
  18:        0x10b418b33 - <F as alloc::boxed::FnBox<A>>::call_box::h7af5270adbc74627
  19:        0x1104b5174 - std::sys::imp::thread::Thread::new::thread_start::h4ad0b40513420e9c
  20:     0x7fff9127a898 - _pthread_body
  21:     0x7fff9127a729 - _pthread_start

error: Could not compile `web`.

To learn more, run the command again with --verbose.
Alexs-MacBook-Air-3:nri alex$ unset CARGO_INCREMENTAL
Alexs-MacBook-Air-3:nri alex$ cargo build
   Compiling web v0.1.0 (file:///Users/alex/Documents/research/proton/code/nri/crates/front/web)
   Compiling nri v0.1.0 (file:///Users/alex/Documents/research/proton/code/nri)
error[E0277]: the trait bound `chrono::DateTime<chrono::UTC>: std::ops::Sub` is not satisfied
   --> src/main.rs:368:68
    |
368 |                             println!("Service {} took {} ms", who, UTC::now() - then);
    |                                                                    ^^^^^^^^^^^^^^^^^ the trait `std::ops::Sub` is not implemented for `chrono::DateTime<chrono::UTC>`
    |
    = help: the following implementations were found:
              <chrono::DateTime<Tz> as std::ops::Sub<chrono::FixedOffset>>
              <chrono::DateTime<Tz> as std::ops::Sub<chrono::Duration>>

error: aborting due to previous error

error: Could not compile `nri`.

To learn more, run the command again with --verbose.
Alexs-MacBook-Air-3:nri alex$

So, there was a breaking change from the upgrade, but with incr comp turned on, it crashed before that point.

[michaelwoerister]

Might be the same root cause as in #39569.
cc @nikomatsakis

[nikomatsakis]

@durka I believe this was fixed, can you verify?

[durka]

I'm not really sure how to reproduce since it was a fleeting Cargo.toml change and furthermore I have a different ICE now. I'll take your word for it :)