[cmake] Build swift-testing with CMake.

[jeffdav]

Add files needed to build swift-testing with CMake.

Motivation:

Being able to build with CMake is useful in many scenarios. The immediate need is to bring swift-testing to Windows. To do so we need to support a non-SPM path to allow building targets that would otherwise hit the export symbol limit on Windows.

Modifications:

• Added CMake files to build Testing, TestingInternal, and TestingMacros.
• Build TestingMacros as an ExternalProject targeting the build machine.
• Add SwiftTesting_GenerateDerivedSources which generates a runner-swift-testing.swift and returns a variable that allows consumers to compile it with their sources.

Result:

• Can build swift-testing with CMake. Example command lines:

cmake -S . -B b -G Ninja -D CMAKE_CXX_COMPILER=clang
cmake --build .\b

• Example diff that converts swift-webdriver to use swift-testing via CMake.

Checklist:

• Code and documentation should follow the style of the Style Guide.
• If public symbols are renamed or modified, DocC references should be updated.

[grynspan]

Thanks for opening this PR! There's still some work to be done, but this is a great start.

[stmontgomery]

Thank you @jeffdav! Appreciate the helpful contribution. I have several comments so far and will take a second pass tomorrow

[grynspan]

Open question: how do we test this change?

[etcwilde]

This is looking good. I think disabling C++ exceptions on _TestingInternal will help make the experience a little smoother, but beyond that, it seems to be working as I would expect. Install story can come later.

[etcwilde]

LGTM

[jeffdav]

@grynspan any further concerns on your side?

[grynspan]

Nope, I defer to @etcwilde here.

(FYI we don't use Swift's C++ interop feature, so its lack of support for exceptions doesn't make a difference to us. However, we also don't throw any exceptions or intend to catch any, so it's moot.)

[grynspan]

Oh—please update the file lists before merging. There are a number of new files added since you opened this PR.

[jeffdav]

Oh—please update the file lists before merging. There are a number of new files added since you opened this PR.

Done!

[grynspan]

@etcwilde

[grynspan]

@swift-ci please test

[grynspan]

@jeffdav I know you folks obviously work with Windows. The Windows failure we're seeing is a compiler bug unrelated to your PR. If you're comfortable with merging the PR despite the failure, we can proceed. (I'm unsure if you can see a merge button—if not, ping me and I'll do it.)

[jeffdav]

@jeffdav I know you folks obviously work with Windows. The Windows failure we're seeing is a compiler bug unrelated to your PR. If you're comfortable with merging the PR despite the failure, we can proceed. (I'm unsure if you can see a merge button—if not, ping me and I'll do it.)

Yeah, I'm familiar with that compiler bug for other reasons. :)

[jeffdav]

@grynspan Thanks for your help! I don't have a merge button.

[grynspan]

@swift-ci please test