fix deprecation warning for Plugin's Path

[sebsto]

Replace the usage of Plugin's Path with URL

Motivation:

Path is deprecated in Swift 6

Modifications:

• Replace the use of Path with URL and adjust path components management accordingly

Result:

no more compilation warnings when compiling the archive plugin on Swift 6

Command to test the plugin with Swift 6

	swift package archive \
		--base-docker-image swiftlang/swift:nightly-6.0-amazonlinux2 \
		--disable-sandbox

[sebsto]

@swift-server-bot test this please

[fabianfett]

I'm afraid we need full Foundation here. This is a built time dependency. So therefore we don't really care.

Suggested change

	#if canImport(FoundationEssentials)
	import FoundationEssentials
	#else
	import struct Foundation.URL
	import class Foundation.ProcessInfo
	import class Foundation.FileManager
	import struct Foundation.ObjCBool
	#endif
	import Foundation

[sebsto]

Correct - just realized that when testing the CI compilation (that failed) - I just pushed a change

[fabianfett]

I think the comment here is misleading. The important thing here is the following. We write to the variable from a single SerialDispatchQueue here. We wait until the process is run below process.waitUntilExit(). This means no further writes to output will happen. This makes it save for us to read the output.

[fabianfett]

We should switch to the new Foundation Process API as soon as it is available:
https://github.com/apple/swift-foundation/blob/main/Proposals/0007-swift-subprocess.md

[sebsto]

Changed to

        // We need to use an unsafe transfer here to get the fd into our Sendable closure.
        // This transfer is fine, because we write to the variable from a single SerialDispatchQueue here.
        // We wait until the process is run below process.waitUntilExit().
        // This means no further writes to output will happen.
        // This makes it save for us to read the output

[sebsto]

Created #364 to keep track of SubProcess

[fabianfett]

Thanks so much! This is so great!