Update catch_unwind doc comments for c_unwind

[BatmanAoD]

Updates catch_unwind doc comments to indicate that catching a foreign exception will no longer be UB. Instead, there are two possible behaviors, though it is not specified which one an implementation will choose.

Nominated for t-lang to confirm that they are okay with making such a promise based on t-opsem FCP, or whether they would like to be included in the FCP.

Related: #74990, #115285, rust-lang/reference#1226

[rustbot]

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[tgross35]

@rustbot author

[rustbot]

There are merge commits (commits with multiple parents) in your changes. We have a no merge policy so these commits will need to be removed for this pull request to be merged.

You can start a rebase with the following commands:

$ # rebase
$ git pull --rebase https://github.com/rust-lang/rust.git master
$ git push --force-with-lease

The following commits are merge commits:

• 4a8fe8c

[BatmanAoD]

@rustbot ready

[rustbot]

There are merge commits (commits with multiple parents) in your changes. We have a no merge policy so these commits will need to be removed for this pull request to be merged.

You can start a rebase with the following commands:

$ # rebase
$ git pull --rebase https://github.com/rust-lang/rust.git master
$ git push --force-with-lease

The following commits are merge commits:

• 8e8a1d0

[BatmanAoD]

@rust-lang/libs I think we need some official sign-off of some sort on this, because it provides a new guarantee that wasn't part of the initial RFC.

If there's agreement that this should be merged, can we also backport it to beta in time for the 1.81 release, so that the documentation will be correct in time for the full stabilization of c_unwind?

[cuviper]

New guarantees should be considered by @rust-lang/libs-api.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[BatmanAoD]

IMO we should "just" document what happens when a foreign unwind (or really, any unwind) leaves main, similar to what we now say for join. But I also don't know where to put this.

I don't see anything about an "entrypoint" in the standard library, but I may just not know what to look for. The other place that might make sense to document this would be, I guess, in the new panic documentation in the Reference, or possibly somewhere else in the Reference?

[RalfJung]

Yeah, the reference docs is the best place I can think of for this right now.

[BatmanAoD]

@RalfJung The other PR mentioned unwinding past main in the "panic" section, but I've explicitly added this information to the fn main documentation as well.

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

[BatmanAoD]

@tgross35 There are now only two commits; do you need me to squash again before merge?

[tgross35]

@tgross35 There are now only two commits; do you need me to squash again before merge?

It's up to whoever approves this, and officially we have no history requirements. But it's always good to avoid making a change in one commit and then immediately undoing/modifying that change in another commit within the same PR, so I would probably squash (history/blame/bisect gets significantly harder to understand otherwise - nbd here, just good practice).

Also, you can drop the Co-authored-by: Trevor Gross ..., that was just a small wording suggestion :)

[Mark-Simulacrum]

I think https://github.com/rust-lang/rust/pull/128321/files#r1750418130 is still unresolved -- it would make sense to me to clarify that behavior in this PR.

[BatmanAoD]

@Mark-Simulacrum resolved.

@tgross35 That was added automatically by GH. 😆 Removed; thank you.