[shims] Remove some obsolete shims modules

[lorentey]

The corresponding overlays are maintained outside of this repository, and they haven’t been importing these shims for years.

SDKs that shipped between Xcode 10.2 and Xcode 11 (or so) contained overlay modules that imported these shims modules, so future toolchain builds won’t work correctly with those SDKs. (This is fine! We do not expect toolchain builds to work with years old Xcode installations anyway.)

The shims that remain are used either by stdlib components, or by one of the overlays that still exist in the repository (ObjectiveC, Darwin, CoreGraphics, CoreFoundation, Foundation).

[lorentey]

@swift-ci test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 928882698a4d7669688c22246459f05a8945924e

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 928882698a4d7669688c22246459f05a8945924e

[lorentey]

19:31:51 
/Users/buildnode/jenkins/workspace/swift-PR-macos/branch-main/swift/stdlib/public/Darwin/XCTest/XCTest.swift:27:29: error: no such module '_SwiftXCTestOverlayShims'
19:31:51 @_implementationOnly import _SwiftXCTestOverlayShims
19:31:51                             ^

Oh yeah, this depends on #37587.

[lorentey]

@swift-ci test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 928882698a4d7669688c22246459f05a8945924e

[lorentey]

01:16:33 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib/XCTest.swiftmodule/x86_64-apple-macos.swiftinterface:8:8: error: no such module '_SwiftXCTestOverlayShims'
01:16:33 import _SwiftXCTestOverlayShims
01:16:33        ^
01:16:33 /Users/buildnode/jenkins/workspace/swift-PR-macos/branch-main/swiftpm/Sources/swiftpm-xctest-helper/main.swift:12:8: error: failed to build module 'XCTest'; this SDK is not supported by the compiler (the SDK is built with 'Apple Swift version 5.3.2 (swiftlang-1200.0.45 clang-1200.0.32.28)', while this compiler is 'Apple Swift version 5.5-dev (LLVM ad98975a96ba709, Swift 7d5e3f1882a6c05)'). Please select a toolchain which matches the SDK.
01:16:33 import XCTest
01:16:33        ^

Well well well, what do we have here.

[lorentey]

Let's pick this up again. The bogus XCTest overlay was removed (#37587) by the time the failing build above started. It is possible we picked up an older version of it from the SDK somehow, in which case we'll probably need to keep the XCTest shims in the toolchain for a year or two yet. But first, let's try again with the current state of this branch.

[lorentey]

@swift-ci test

[lorentey]

It is possible we picked up an older version of it from the SDK somehow

Ah, the console logs were in fact pretty clear about the issue -- the version of the real XCTest overlay in the Xcode we currently use in CI (Xcode 12.3 (12C33)) apparently still imports the old toolchain shims:

01:16:33 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib/XCTest.swiftmodule/x86_64-apple-macos.swiftinterface:8:8: error: no such module '_SwiftXCTestOverlayShims'

This is unexpected, as I thought these imports were removed as far back as Xcode 11.4 (or so). 🤔

[lorentey]

Oh, a stray import remained until Xcode 12.5. That's okay -- we just need to keep the XCTest shims around a bit longer.

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 928882698a4d7669688c22246459f05a8945924e

[lorentey]

@swift-ci test