Fix a build failure on Windows (#4224)

[kkebo]

This is a hot fix for Windows build broken by #4224. #4231 also needs this change.

Motivation:

#4224 broke Windows build as @compnerd pointed out at #4224 (comment). The global function exec added in #4224 is actually unnecessary for Windows because signal(SIGINT, SIG_IGN) is not compiled for Windows target.

            #if os(Windows)
            // set shutdown handler to terminate sub-processes, etc
            SwiftTool.cancellator = cancellator
            _ = SetConsoleCtrlHandler({ _ in
                // Terminate all processes on receiving an interrupt signal.
                try? SwiftTool.cancellator?.cancel(deadline: .now() + .seconds(30))

                // Reset the handler.
                _ = SetConsoleCtrlHandler(nil, false)

                // Exit as if by signal()
                TerminateProcess(GetCurrentProcess(), 3)

                return true
            }, true)
            #else
            // trap SIGINT to terminate sub-processes, etc
            signal(SIGINT, SIG_IGN)
            ...
            #endif

Modifications:

• Enclosed exec with #if !(os(Windows)) and #endif
• Changed comments to be clearer

Result:

Combined with this change, #4224 no longer affects Windows.

[compnerd]

@swift-ci please smoke test

[compnerd]

I think that we should really revert the change - its incomplete - this should have an analogous counterpart to Windows. (Having a separate exec is likely going to cause further conflicts as things evolve ... this should handle the Windows path internally).

[kkebo]

@compnerd

(Having a separate exec is likely going to cause further conflicts as things evolve ... this should handle the Windows path internally).

I initially considered alternatives such as SwiftTool.exec. However, there is a concern that when changes are made to add TSCBasic's exec in the future, the author may forget to use SwiftTool.exec.

In light of that, it might be better to revert and reimplement #3815 in other ways.

this should have an analogous counterpart to Windows.

I think that would be the most ideal too.

[compnerd]

I initially considered alternatives such as SwiftTool.exec. However, there is a concern that when changes are made to add TSCBasic's exec in the future, the author may forget to use SwiftTool.exec.

I think that we could just bring over exec from TSCBasic. I haven't gotten around to removing the last of the TSCUtility from swift-driver, which would then allow us to focus on removing the uses of TSCBasic. Doing that more immediately is reasonable. We should be able to entirely remove the use of TSCBasic.exec and use the internal exec only.

[kkebo]

TSCBasic provides other types and operators as well, so it's difficult for me to determine if TSCBasic should be removed.

By any chance, could your concern be addressed with code such as the following?

func exec(...) {
    #if !(os(Windows))
    // signal(SIGINT, SIG_IGN) is used for handling SIGINT by DispatchSourceSignal,
    // but this process is about to be replaced by exec, so SIG_IGN must be returned to default.
    signal(SIGINT, SIG_DFL)
    #endif

    TSCBasic.exec(...)
}

...

public class SwiftTool {
    ...

    // marked internal for testing
    internal init(outputStream: OutputByteStream, options: GlobalOptions) throws {
        ...

        do {
            ...

            #if os(Windows)
            ...
            #else
            ...
            signal(SIGINT, SIG_IGN)
            ...
            #endif

            ...
        } catch {
            ...
        }

        ...
    }

    ...
}

...

[tomerd]

@swift-ci please smoke test macOS

[compnerd]

Yeah, I think that would be better than the current version.

[kkebo]

@compnerd I pushed that change.

@tomerd Sorry for the change after you approve. Please could you check it again?

[tomerd]

@swift-ci smoke test

[tomerd]

no problem @KKK669 please bring this commit over to the 5.6 PR once merged

[kkebo]

Yes sure. Thank you.

[tomerd]

@swift-ci smoke test linux

[compnerd]

@swift-ci please smoke test Linux platform

[tomerd]

@swift-ci smoke test linux

[tomerd]

@swift-ci smoke test linux

[tomerd]

@swift-ci smoke test linux

[compnerd]

@swift-ci please smoke test Linux platform