Add a test documenting the current state of C++ exception handling

[martinboehme]

Swift currently allows C++ exceptions to propagate across Swift stack frames, which is wrong; this test documents that, but also the current behaviors that are fine.

See also the discussion here:
https://forums.swift.org/t/handling-c-exceptions/34823

I'm not sure whether this test will on all platforms, particularly Windows. I may restrict it to certain platforms if build bots show it doesn't work everywhere.

[gribozavr]

@swift-ci Please smoke test

[gribozavr]

@swift-ci Please test Windows

[gribozavr]

@swift-ci Please test Windows

[gribozavr]

@swift-ci Please smoke test Windows

[martinboehme]

I was hoping that linking libstdc++ explicitly in the module map would make this test work at least on macOS as well as Linux, but that doesn't seem to be the case.

So I think I'll have to do the right fix first, which is to make Swift link against the correct library for each platform when -enable-cxx-interop is specified.

Until that's done, I'm not looking for further review on this PR. What is the right way to do this -- just leave this PR open with this comment? (If I close it and reopen a new PR, the previous discussion will be lost, which seems undesirable.)

[gribozavr]

We can leave it open while it is blocked. Just make sure to close it should plans change and you decide to take another approach.

[martinboehme]

Thanks, will do!

[compnerd]

Also note that there is a third C++ library that you need to be aware of: msvcprt.

[compnerd]

@swift-ci please test Windows platform

[martinboehme]

Also note that there is a third C++ library that you need to be aware of: msvcprt.

Thanks for the heads-up!

As I mention above, I've come to the conclusion that it's really not a sustainable approach to link to all the platform-specific libraries locally in this test. Instead, Swift should generally link against the right C++ libraries when -enable-cxx-interop is enabled:

https://bugs.swift.org/browse/SR-12469

I'm pausing this PR until that bug is fixed.

[shahmishal]

Please update the base branch to main by Oct 5th otherwise the pull request will be closed automatically.

• How to change the base branch: (Link)
• More detail about the branch update: (Link)