Prune stacktraces for tag-tracking diagnostics too

[saethlin]

In #1977 we forgot to use the pruning logic when printing tag-tracking messages. I just saw this output before this PR which is very silly:

test sanity ... note: tracking was triggered
   --> src/lib.rs:110:21
    |
110 |         unsafe { &*(&self.value[range] as *const [T] as *const Aligned<A, [T]>) }
    |                     ^^^^^^^^^^^^^^^^^^ created tag 160954
    |
    = note: inside `<Aligned<A4, [u8]> as std::ops::Index<std::ops::RangeTo<usize>>>::index` at src/lib.rs:110:21
note: inside `sanity` at src/lib.rs:261:30
   --> src/lib.rs:261:30
    |
261 |     let y: &Aligned<_, _> = &y[..2];
    |                              ^^^^^^
note: inside closure at src/lib.rs:229:1
   --> src/lib.rs:229:1
    |
228 |   #[test]
    |   ------- in this procedural macro expansion
229 | / fn sanity() {
230 | |     use core::mem;
231 | |
232 | |     let x: Aligned<A2, _> = Aligned([0u8; 3]);
...   |
284 | |     let _: &[u8] = y;
285 | | }
    | |_^
    = note: inside `<[closure@src/lib.rs:229:1: 285:2] as std::ops::FnOnce<()>>::call_once - shim` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/core/src/ops/function.rs:227:5
    = note: inside `<fn() as std::ops::FnOnce<()>>::call_once - shim(fn())` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/core/src/ops/function.rs:227:5
    = note: inside `test::__rust_begin_short_backtrace::<fn()>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/test/src/lib.rs:575:5
    = note: inside closure at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/test/src/lib.rs:566:30
    = note: inside `<[closure@test::run_test::{closure#1}] as std::ops::FnOnce<()>>::call_once - shim(vtable)` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/core/src/ops/function.rs:227:5
    = note: inside `<std::boxed::Box<dyn std::ops::FnOnce() + std::marker::Send> as std::ops::FnOnce<()>>::call_once` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/alloc/src/boxed.rs:1854:9
    = note: inside `<std::panic::AssertUnwindSafe<std::boxed::Box<dyn std::ops::FnOnce() + std::marker::Send>> as std::ops::FnOnce<()>>::call_once` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/core/src/panic/unwind_safe.rs:271:9
    = note: inside `std::panicking::r#try::do_call::<std::panic::AssertUnwindSafe<std::boxed::Box<dyn std::ops::FnOnce() + std::marker::Send>>, ()>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/panicking.rs:492:40
    = note: inside `std::panicking::r#try::<(), std::panic::AssertUnwindSafe<std::boxed::Box<dyn std::ops::FnOnce() + std::marker::Send>>>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/panicking.rs:456:19
    = note: inside `std::panic::catch_unwind::<std::panic::AssertUnwindSafe<std::boxed::Box<dyn std::ops::FnOnce() + std::marker::Send>>, ()>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/panic.rs:137:14
    = note: inside `test::run_test_in_process` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/test/src/lib.rs:598:18
    = note: inside closure at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/test/src/lib.rs:492:39
    = note: inside `test::run_test::run_test_inner` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/test/src/lib.rs:530:13
    = note: inside `test::run_test` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/test/src/lib.rs:562:28
    = note: inside `test::run_tests::<[closure@test::run_tests_console::{closure#2}]>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/test/src/lib.rs:305:17
    = note: inside `test::run_tests_console` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/test/src/console.rs:286:5
    = note: inside `test::test_main` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/test/src/lib.rs:116:15
    = note: inside `test::test_main_static` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/test/src/lib.rs:135:5
    = note: inside `main`
    = note: inside `<fn() as std::ops::FnOnce<()>>::call_once - shim(fn())` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/core/src/ops/function.rs:227:5
    = note: inside `std::sys_common::backtrace::__rust_begin_short_backtrace::<fn(), ()>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/sys_common/backtrace.rs:122:18
    = note: inside closure at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/rt.rs:145:18
    = note: inside `std::ops::function::impls::<impl std::ops::FnOnce<()> for &dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>::call_once` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/core/src/ops/function.rs:259:13
    = note: inside `std::panicking::r#try::do_call::<&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe, i32>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/panicking.rs:492:40
    = note: inside `std::panicking::r#try::<i32, &dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/panicking.rs:456:19
    = note: inside `std::panic::catch_unwind::<&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe, i32>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/panic.rs:137:14
    = note: inside closure at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/rt.rs:128:48
    = note: inside `std::panicking::r#try::do_call::<[closure@std::rt::lang_start_internal::{closure#2}], isize>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/panicking.rs:492:40
    = note: inside `std::panicking::r#try::<isize, [closure@std::rt::lang_start_internal::{closure#2}]>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/panicking.rs:456:19
    = note: inside `std::panic::catch_unwind::<[closure@std::rt::lang_start_internal::{closure#2}], isize>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/panic.rs:137:14
    = note: inside `std::rt::lang_start_internal` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/rt.rs:128:20
    = note: inside `std::rt::lang_start::<()>` at /home/ben/.rustup/toolchains/miri/lib/rustlib/src/rust/library/std/src/rt.rs:144:17
    = note: this note originates in the attribute macro `test` (in Nightly builds, run with -Z macro-backtrace for more info)

error: Undefined Behavior: trying to reborrow for SharedReadOnly at alloc61593+0x2, but parent tag <160954> does not have an appropriate item in the borrow stack
   --> src/lib.rs:261:30
    |
261 |     let y: &Aligned<_, _> = &y[..2];
    |                              ^^^^^^ trying to reborrow for SharedReadOnly at alloc61593+0x2, but parent tag <160954> does not have an appropriate item in the borrow stack
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the rules it violated are still experimental
    = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
            
    = note: inside `sanity` at src/lib.rs:261:30
note: inside closure at src/lib.rs:229:1
   --> src/lib.rs:229:1
    |
228 |   #[test]
    |   ------- in this procedural macro expansion
229 | / fn sanity() {
230 | |     use core::mem;
231 | |
232 | |     let x: Aligned<A2, _> = Aligned([0u8; 3]);
...   |
284 | |     let _: &[u8] = y;
285 | | }
    | |_^
    = note: this error originates in the attribute macro `test` (in Nightly builds, run with -Z macro-backtrace for more info)

note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

error: aborting due to previous error

error: test failed, to rerun pass '--lib'

[oli-obk]

@bors r+

[bors]

📌 Commit d2bb231 has been approved by oli-obk

[bors]

⌛ Testing commit d2bb231 with merge 144d565...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 144d565 to master...

[RalfJung]

That seems very fragile, since it relies on a detail inside another function.

I think either prune_stacktrace should return a bool to indicate whether anything was pruned, or we just always print this because it's not a big deal.

[saethlin]

Hm, I agree. Then here we could only check if the trace was pruned.

[RalfJung]

Yeah. Would you like to submit a PR for that?