remap libstd paths in backtraces for test crates

[jonas-schievink]

I just got this backtrace when running RUST_BACKTRACE=1 cargo test on salsa-rs/salsa@bb4b42a:

thread 'frozen::in_par_get_set_cancelation' panicked at 'called `Result::unwrap()` on an `Err` value: Any { .. }', tests/parallel/frozen.rs:64:33
stack backtrace:
   0: rust_begin_unwind
             at /rustc/881c1ac408d93bb7adaa3a51dabab9266e82eee8/library/std/src/panicking.rs:493:5
   1: core::panicking::panic_fmt
             at /rustc/881c1ac408d93bb7adaa3a51dabab9266e82eee8/library/core/src/panicking.rs:92:14
   2: core::result::unwrap_failed
             at /rustc/881c1ac408d93bb7adaa3a51dabab9266e82eee8/library/core/src/result.rs:1355:5
   3: core::result::Result<T,E>::unwrap
             at /home/jonas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/result.rs:1037:23
   4: parallel::frozen::in_par_get_set_cancelation
             at ./tests/parallel/frozen.rs:64:18
   5: parallel::frozen::in_par_get_set_cancelation::{{closure}}
             at ./tests/parallel/frozen.rs:13:1
   6: core::ops::function::FnOnce::call_once
             at /home/jonas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:227:5
   7: core::ops::function::FnOnce::call_once
             at /rustc/881c1ac408d93bb7adaa3a51dabab9266e82eee8/library/core/src/ops/function.rs:227:5

The remapping from /rustc/... paths to the rust-src component only seems to kick in once here, but I expected it to always work (since the component is installed). Frames 6 and 7 also point to the exact same location, but path remapping still failed for one of them.

[jyn514]

@jonas-schievink what version of rustc is this?

[jonas-schievink]

This is on rustc 1.54.0-nightly (881c1ac40 2021-05-08)

[jyn514]

Can you try with latest nightly? #83813 was merged recently and may have fixed this.

[jonas-schievink]

The most recent nightly seems to work even less:

thread 'frozen::in_par_get_set_cancelation' panicked at 'called `Result::unwrap()` on an `Err` value: Any { .. }', tests/parallel/frozen.rs:64:33
stack backtrace:
   0: rust_begin_unwind
             at /rustc/4e3e6db011c5b482d2bef8ba02274657f93b5e0d/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/4e3e6db011c5b482d2bef8ba02274657f93b5e0d/library/core/src/panicking.rs:92:14
   2: core::result::unwrap_failed
             at /rustc/4e3e6db011c5b482d2bef8ba02274657f93b5e0d/library/core/src/result.rs:1355:5
   3: core::result::Result<T,E>::unwrap
             at /rustc/4e3e6db011c5b482d2bef8ba02274657f93b5e0d/library/core/src/result.rs:1037:23
   4: parallel::frozen::in_par_get_set_cancelation
             at ./tests/parallel/frozen.rs:64:18
   5: parallel::frozen::in_par_get_set_cancelation::{{closure}}
             at ./tests/parallel/frozen.rs:13:1
   6: core::ops::function::FnOnce::call_once
             at /rustc/4e3e6db011c5b482d2bef8ba02274657f93b5e0d/library/core/src/ops/function.rs:227:5
   7: core::ops::function::FnOnce::call_once
             at /rustc/4e3e6db011c5b482d2bef8ba02274657f93b5e0d/library/core/src/ops/function.rs:227:5

[jyn514]

@jonas-schievink what do you mean? Those look correctly remapped to /rustc/hash to me, were you expecting something else?

[jyn514]

Oh I see, you want it to not remap and use the local path.

[jyn514]

Note that people have requested the opposite behavior in the past, but it seems reasonable to do this only for tests: #82188

[jonas-schievink]

The /rustc/<hash> path is the non-remapped path. I have the rust-src component installed, so they should be remapped to point there. (my mistake, the terminology used here wasn't clear to me)

[jyn514]

cc @cbeuw