Print thread ID in panic message

[tgross35]

panic! does not print any identifying information for threads that are
unnamed. However, in many cases, the thread ID can be determined.

This changes the panic message from something like this:

thread '<unnamed>' panicked at src/main.rs:3:5:
explicit panic

To something like this:

thread '<unnamed>' (12345) panicked at src/main.rs:3:5:
explicit panic

Stack overflow messages are updated as well.

This change applies to both named and unnamed threads. The ID printed is
the OS integer thread ID rather than the Rust thread ID, which should
also be what debuggers print.

try-job: aarch64-apple
try-job: aarch64-gnu
try-job: dist-apple-various
try-job: dist-various-*
try-job: dist-x86_64-freebsd
try-job: dist-x86_64-illumos
try-job: dist-x86_64-netbsd
try-job: dist-x86_64-solaris
try-job: test-various
try-job: x86_64-gnu
try-job: x86_64-mingw-1
try-job: x86_64-msvc-1

[rustbot]

r? @davidtwco

(rustbot has picked a reviewer for you, use r? to override)

[tgross35]

I think this needs FCP since it's a visible change

@rustbot label -T-libs -T-compiler +T-libs-api
r? libs-api

[rustbot]

The Miri subtree was changed

cc @rust-lang/miri

[tgross35]

cc @m-ou-se since you recently did the formatting in #112849

[bjorn3]

Maybe

thread '<unnamed 2>' panicked at src/main.rs:3:5:
explicit panic

or

thread '<unnamed#2>' panicked at src/main.rs:3:5:
explicit panic

? That fits more with the way named threads are shown.

[the8472]

Note that this is a rust-internal thread ID, which isn't the OS thread ID which can be relevant if you're also logging from C code or looking at things with GDB. And as_u64() is unstable and there are questions about stabilizing it (#110738).

[tgross35]

Maybe

thread '<unnamed 2>' panicked at src/main.rs:3:5:
explicit panic

or

thread '<unnamed#2>' panicked at src/main.rs:3:5:
explicit panic

I just proposed the syntax as a demo, figured libs-api would make the final choice - though between those two, I like the first one better

Note that this is a rust-internal thread ID, which isn't the OS thread ID which can be relevant if you're also logging from C code or looking at things with GDB. And as_u64() is unstable and there are questions about stabilizing it (#110738).

It is kind of unfortunate that Rust and C won't use the same thread IDs. But this seems worthwhile still - Rust-only applications printing the thread ID in logs is common (tracing even has a builtin way to do this), probably more common than Rust thread IDs silently mixing with C thread IDs in logs. And even in that case, it still gives you something more concrete to trace than "something failed".

This is all inspired by the below failure I recently had in an highly threaded system. The entire backtrace uselessly displayed one repeated function, with no hints about which preceding log events were relevant:

thread '<unnamed>' panicked at src/scan.rs:101:55:
called `Result::unwrap()` on an `Err` value: ()
stack backtrace:
   0:        0x1009661d0 - __mh_execute_header
   1:        0x10088869b - __mh_execute_header
   2:        0x10093ba0e - __mh_execute_header
   4:        0x10096757c - __mh_execute_header
   5:        0x100968632 - __mh_execute_header
   6:        0x1009680f4 - __mh_execute_header
   7:        0x100968059 - __mh_execute_header
   8:        0x100968042 - __mh_execute_header
   9:        0x100bdd913 - __mh_execute_header

I don't think that stability of the thread ID is much of a concern since we will always have some integer ID for a thread, even if the semantics of that ID might change. The important thing is probably just that this panic message thread ID is the same as what shows up as Debug for ThreadId (or as_u64 as applicable) since that is what other libraries are directed to use. That is the case here

[tgross35]

Another display option - it looks a bit cleaner to not even call out that a thread is unnamed, and I don't think it adds much

thread with ID 2 panicked at src/main.rs:3:5:
explicit panic

Or we could use ThreadId's debug formatting which tracing and I think log do, but that seems unnecessarily clunky

thread with `ThreadId(2)` panicked at src/main.rs:3:5:
explicit panic

I also tried to poke some discussion at #67939

[bors]

☔ The latest upstream changes (presumably #115627) made this pull request unmergeable. Please resolve the merge conflicts.

[tgross35]

@joshtriplett do you have any thoughts on this?

[timClicks]

Sorry to add bike shedding to the thread. Here is a slight derivative of the last suggestion, which omits a "with":

thread `ThreadId(2)` panicked at src/main.rs:3:5:
explicit panic

Although it's uglier than using the thread identifier in a sentence, using the Debug form makes it look like a Rust value rather than something else. It's also consistent with other output from Rust, although the case can definitely be made that thread IDs deserve a special case.

[tgross35]

I know Josh has a pretty busy queue, so perhaps it is best to reroll

r? libs-api

[dtolnay]

I think this needs FCP since it's a visible change

@​rustbot label -T-libs -T-compiler +T-libs-api

I think it wouldn't need one. T-libs-api FCP is primarily for any time a permanent API commitment is being made by the standard library, and deprecations. In contrast, anything that we can just change back with minimal effort or disruption would not warrant FCP.

#112849 had a T-libs FCP but I am not familiar with their criteria for that. @rust-lang/libs would you want to handle this PR?

In any case, this looks good to me.

[thomcc]

I don't know that this needs FCP. I'm not opposed and there is precedent for it, but OTOH we wouldn't FCP a panic message change somewhere in the stdlib. So I don't feel strongly.

In any case, I think this change is a good idea, and am in favor.

[RalfJung]

Sync completed in #143478.

[tgross35]

Rebased on top of the Miri sync, updated for Solaris, Illumos, and SGX (verified locally that they check correctly). I didn't update redox gettid isn't yet in libc.

Large list since this touches a lot of platform:
@bors2 try

[rustbot]

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

[tgross35]

@bors2 try cancel
@bors2 try

[rust-bors]

Try build cancelled. Cancelled workflows:

• https://github.com/rust-lang/rust/actions/runs/16104090308

[rust-bors]

⌛ Trying commit 4bfafd8 with merge 886d475…

To cancel the try build, run the command @bors2 try cancel.

[rust-bors]

☀️ Try build successful (CI)
Build commit: 886d475 (886d4752ec85d06c58c96ffb5379dc0fe5751ec9, parent: a84ab0ce6c4557a2f01a3a6c3fdb0f92098db78d)

[RalfJung]

(FYI, bors2 try will automatically cancel a previous try build if it is still running.)

[tgross35]

@rustbot ready