PathCchIsRoot Updated isRoot extension.

[macshome]

Now that swiftlang/swift-foundation#976 and swiftlang/swift-foundation#980 are fixed we can clean this code up a bit by removing the empty path check on Linux and by using the native PathCchIsRoot on Windows.

The isRoot extension now uses native Windows and macOS API and has the Linux tests cleaned up.

• macOS root is determined by comparing the path to NSOpenStepRootDirectory()
• Windows root is determined by a call to PathCchIsRoot
• Linux root is determined by a comparison to "/"
• Non-filesystem type URLs always return false as they can't be a filesystem root.

Fixes: #844

All tests pass on macOS and Windows 11.

[ahoppen]

We can’t switch this unconditionally yet because those fixes aren’t in Swift 6.0 toolchains. I think we need to guard this by #if compiler(>=6.1) and fall back to the old behavior if not.

[macshome]

OK, I gated the new behavior behind a check for >=6.1. Below that the old code is still in place. The Mac behavior isn't gated as it most certainly isn't new. 😄

[ahoppen]

path will be the URL path components. We should use filePath or withUnsafeFileSystemRepresentation instead.

[ahoppen]

This should be #else. Otherwise this function doesn’t have a return value eg. on platforms that are neither macOS, Linux, nor Windows, like Android.

[macshome]

I had that thought and will fix it.

[ahoppen]

I would change this to #elseif compiler(>=6.1) to ensure we don’t get any of the returns below for macOS

[macshome]

OK. I updated with the suggested changes, but note that I don't have my Windows setup with me right now. If someone can run the tests on Windows it would be great.

[ahoppen]

I updated your branch make it build on Windows. I also removed the macOS-specific call to NSOpenStepRootDirectory. It’s effectively / and I would prefer to not have the code between macOS and Linux unless necessary.