Duplicate `main` symbol for `swift test` on Windows

[remko]

Description

I have a package with an executable target, and a test target. The tests in the test target do a @testable import of the executable target. The main target has a @main struct ....

Running swift test works on macOS and Linux.
Running swift test on Windows fails.

Expected behavior

When running swift test on Windows, the tests run.

Actual behavior

When running swift test on windows, it fails with an error at link time:

lld-link: error: duplicate symbol: main
>>> defined at C:\\...\\MyPackageTests.build\\runner.swift.o
>>> defined at C:\\...\\MyPackage\\MyMainStruct.swift.o

Steps to reproduce

No response

Swift Package Manager version/commit hash

version included in the official Swift download for Windows

Swift & OS version (output of swift --version && uname -a)

Swift: 5.8
OS: Microsoft Windows Server 2022

(also happens on other versions of swift and OS).

[neonichu]

Sounds as if -entry-point-function-name is maybe not working correctly on Windows? We could disable the feature via BuildParameters.canRenameEntrypointFunctionName if it doesn't work there.

cc @compnerd

[compnerd]

@neonichu that definitely works: https://github.com/compnerd/swift-win32-application/blob/main/Package.swift even has an example. The problem is that you cannot alias functions using the linker on Windows and this needs to be done in SPM.

[compnerd]

https://github.com/apple/swift-package-manager/blob/main/Sources/Build/BuildPlan.swift#L138-L151

[compnerd]

I think that I have a solution to this that is cross-platform as long as we are reliant on LLVM! The symbol rewriter should do this properly on all file formats!

[dabrahams]

Oof; I should have searched for this before creating the minimal reproducer. But there it is in case it helps! Be sure you get the spm-bug-windows-test-executable-dependency tag.

[grynspan]

@MaxDesiatov Do you think this issue would be resolved now with your cross-compilation macros work?

[compnerd]

I'm still seeing it recently with swift-foundation at least.