[build-script] Add support for building static XCTest

[keith]

Depends on:

• Fix static linking swift-corelibs-xctest#551
• Fix static linking swift-testing#1815
• Fix importing dispatch's static build with cmake swift-corelibs-libdispatch#951

Work towards swiftlang/swift-package-manager#5590

[keith]

@swift-ci please test

[keith]

swiftlang/swift-testing#1815
swiftlang/swift-corelibs-xctest#551
swiftlang/swift-corelibs-libdispatch#951

@swift-ci please build toolchain Ubuntu 24.04

[finagolfin]

Would be great if we could add this for Android too, pinging @swiftlang/android-workgroup if anyone wants to work on it.

[compnerd]

I'm not sure if static linking XCTest is actually supported; CC: @grynspan @stmontgomery @briancroom

[grynspan]

It is not supported, no. On non-Apple platforms, it's technically feasible but comes with a bunch of questions we need to answer first; on Apple platforms, it's not really possible because XCTest and Swift Testing are distributed with Xcode as frameworks.

[keith]

it's technically feasible but comes with a bunch of questions we need to answer first

is there context on this I can read up on?

This is intended only for non-apple platforms (specifically I'm most interested in Linux)

[keith]

swiftlang/swift-testing#1815
swiftlang/swift-corelibs-xctest#551
swiftlang/swift-corelibs-libdispatch#951

@swift-ci please build toolchain Ubuntu 24.04

[grynspan]

it's technically feasible but comes with a bunch of questions we need to answer first

is there context on this I can read up on?

No as I don't think we've even defined all the questions. But in general, if you statically link to Swift Testing or XCTest, you've now got a copy in your executable that could end up shipping to customers. That's not something we want to enable.

This is intended only for non-apple platforms (specifically I'm most interested in Linux)

Changes to Swift Testing or XCTest need to take Apple platforms into account too. While you're not interested in them, we are.

[keith]

swiftlang/swift-testing#1815
swiftlang/swift-corelibs-xctest#551
swiftlang/swift-corelibs-libdispatch#951

@swift-ci please build toolchain Ubuntu 24.04

[keith]

But in general, if you statically link to Swift Testing or XCTest, you've now got a copy in your executable that could end up shipping to customers.

I think this concern is mostly around how we surface this from the build system? For the swiftpm use case users doing swift test --swift-static-stdlib should not ship that binary, and that would cause issues today if they did as well.

Changes to Swift Testing or XCTest need to take Apple platforms into account too. While you're not interested in them, we are.

I didn't mean to imply that I don't care about Apple platforms with this change, just that the intent of this change is to have no effect on toolchains targeting Apple platforms. Please left a comment on the code if you see somewhere where that's not the case! If you think it's worth it we can add some hard fails in the various cmake files if you even attempt to build the static variants targeting macOS.