Windows: Test failing due to assert in computing relative path.

[kcieplak]

Is it reproducible with SwiftPM command-line tools: swift build, swift test, swift package etc?

• Confirmed reproduction steps with SwiftPM CLI. The description text must include reproduction steps with either of command-line SwiftPM commands, swift build, swift test, swift package etc.

Description

The packageInitExecutable test in SwiftPMTests, attempts to build then execute a binary. When building using the native build system, the build succeeds but then fails to execute. The TSCBasic/Paths AbsolutePath extension is asserting causing a failure.

[2025-05-01T15:00:18.097Z]   TSCBasic/Path.swift:969: Assertion failed
[2025-05-01T15:00:18.097Z] 
[2025-05-01T15:00:18.097Z]   Current stack trace:
[2025-05-01T15:00:18.097Z] 
[2025-05-01T15:00:18.097Z]   0    swiftCore.dll                      0x00007ffc00908a80 swift_reportError + 94
[2025-05-01T15:00:18.097Z] 
[2025-05-01T15:00:18.097Z]   1    swiftCore.dll                      0x00007ffc009a5bb0 swift_stdlib_reportFatalErrorInFile + 132
[2025-05-01T15:00:18.097Z] 
[2025-05-01T15:00:18.097Z]   2    swiftCore.dll                      0x00007ffc00618900 StaticString.withUTF8Buffer<A>(_:) + 1828
[2025-05-01T15:00:18.097Z] 
[2025-05-01T15:00:18.097Z]   3    swiftCore.dll                      0x00007ffc00618900 StaticString.withUTF8Buffer<A>(_:) + 1239
[2025-05-01T15:00:18.097Z] 
[2025-05-01T15:00:18.097Z]   4    swiftCore.dll                      0x00007ffc00618900 StaticString.withUTF8Buffer<A>(_:) + 917
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   5    swiftCore.dll                      0x00007ffc00617ab0 _assertionFailure(_:_:file:line:flags:) + 326
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   6    swift-run.exe                      0x00007ff79d8480d0 AbsolutePath.relative(to:) + 3703
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   7    swift-run.exe                      0x00007ff799db1c4b <unavailable> + 990283
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   8    swift-run.exe                      0x00007ff79a54a7ff <unavailable> + 8955903
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   9    swift-run.exe                      0x00007ff79a546831 <unavailable> + 8939569
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   10   swift_Concurrency.dll              0x00007ffc0710e5d0 AsyncMapSequence.transform.getter + 20830
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   11   swift_Concurrency.dll              0x00007ffc071141a0 swift_job_run + 114
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   12   dispatch.dll                       0x00007ffc02efa920 dispatch_assert_queue_barrier + 1008
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   13   dispatch.dll                       0x00007ffc02efa920 dispatch_assert_queue_barrier + 632
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   14   dispatch.dll                       0x00007ffc02f02d80 dispatch_prohibit_transition_to_multithreaded + 8323
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   15   ucrtbase.dll                       0x00007ffc20da6af0 recalloc + 92
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   16   KERNEL32.DLL                       0x00007ffc21504ca0 BaseThreadInitThunk + 16
[2025-05-01T15:00:18.098Z] 
[2025-05-01T15:00:18.098Z]   17   ntdll.dll                          0x00007ffc22fdeda0 RtlUserThreadStart + 43

Expected behavior

No response

Actual behavior

No response

Steps to reproduce

cd IntegrationTests
swift test --filter packageInitExecutable

Swift Package Manager version/commit hash

No response

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

No response

[kcieplak]

related to #8511

[kcieplak]

This is another case of path handling and not dealing with windows paths properly.

In cases where we are creating paths by combining a root and relative path, if that path is greater than PATH_MAX (260) characters then the path will come back as a long path which windows supports in many of thier API calls. i.e.

C:\super-long.........path will become \\?\C:\super-long.......path

The\\?\is used to indicate this is a UNC long path. See https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation?tabs=registry

In the TSC path module, there are uses of PathAllocCombine to join paths and this is what converts to long UNC paths.

There is a bunch of code in the Path.swift that assumes a path is \ separated, which causes issues. It also has issues since it never represents a AbsolutePath the UNC version of path, but does comparisons with the UNC version, in certain cases!

We only see this is the path is longer than 260 chars. In SPM there is at least one case which is interesting, combining a root directory and another directory to make a long path. Note the two occurrences of C:

C:\Users\kcieplak\AppData\Local\Temp\Miscellaneous_Plugins.TJTA5p\MySourceGenPlugin\.build\plugins\outputs\mysourcegenplugin\MyLocalTool\destination\MySourceGenBuildToolPlugin\C:\Users\kcieplak\AppData\Local\Temp\Miscellaneous_Plugins.TJTA5p\MySourceGenPlugin\Sources\MyLocalTool\foo.swift

** Note this is not a valid path in windows, as colon is a reserved character! So this would likely explode in other spots.

[dschaefer2]

According to this, the C: drive would be \\server\C$\ in UNC. https://learn.microsoft.com/en-us/dotnet/standard/io/file-path-formats

[dschaefer2]

Ah, lower down they do mention DOS device paths:

\\.\C:\Test\Foo.txt \\?\C:\Test\Foo.txt

[dschaefer2]

Also interesting that neither cmd or powershell support those as valid paths. But super fascinating that git bash does...

[jakepetroules]

cmd and powershell both supports UNC paths, cmd just doesn't support them as current directories.

[kcieplak]

So the trigger on the long path is caused by a build command plugin that when creating the build commands computes the output file path calling into the PackagePlugin Path Interface

func createBuildCommands(context: PluginContext, target: Target) throws -> [Command] {
        guard let target = target as? SourceModuleTarget else { return [] }
        return try target.sourceFiles.map{ $0.path }.compactMap {
            guard $0.extension == "dat" else { return .none }
            let outputName = $0.stem + ".swift"
            let outputPath = context.pluginWorkDirectory.appending(outputName)
            return .buildCommand(
                displayName:
                    "\(verb) \(outputName) from \($0.lastComponent)",
                executable:
                    try context.tool(named: "MySourceGenBuildTool").path,
                arguments: [
                    "\($0)",
                    "\(outputPath)"
                ],
                inputFiles: [
                    $0,
                ],
                outputFiles: [
                    outputPath
                ]
            )
        }
    }
}

target.sourceFiles.map{ $0.path } is of type Path See: https://github.com/swiftlang/swift-package-manager/blob/main/Sources/PackagePlugin/Path.swift

The Path interface is not compatible with Windows at all looking for Unix / path separators.

let outputName = $0.stem + ".swift"
let outputPath = context.pluginWorkDirectory.appending(outputName)

Will take result in the $0.stem being the full absolute path to the source file:
C:\Users\kcieplak\AppData\Local\Temp\Miscellaneous_Plugins.Jlx8BR\MySourceGenPlugin\Sources\MyLocalTool\foo.swift

Appending that to the working directory of:

\C:\Users\kcieplak\AppData\Local\Temp\Miscellaneous_Plugins.Jlx8BR\MySourceGenPlugin\.build\plugins\outputs\mysourcegenplugin\MyLocalTool\destination\MySourceGenBuildToolPlugin\

This creates a path that is firstly incorrect, as it should simply be working directory and .swift, but also is greater than PATH_MAX, so it triggers issues in the swift-tools-support-core implementation of AbsolutePath.

C:\Users\kcieplak\AppData\Local\Temp\Miscellaneous_Plugins.Jlx8BR\MySourceGenPlugin\.build\plugins\outputs\mysourcegenplugin\MyLocalTool\destination\MySourceGenBuildToolPlugin\C:\Users\kcieplak\AppData\Local\Temp\Miscellaneous_Plugins.Jlx8BR\MySourceGenPlugin\Sources\MyLocalTool\foo.swift

Fixing swift-tools-support-core needs to be done, as paths greater than PATH_MAX could occur in the wild, however it will not fix this issue as the combining logic creates not just a long path but an invalid one.

Moving the test fixtures to use URL instead of Path, will make the plugins use Foundation URL under the covers which should eliminate the bad computation of the stem. The Path Interface is marked as deprecated as of 6.0 in favour of using URL.

This means that build command plugins will have the caveat of only working on Windows when using URL.

[kcieplak]

Fixes in swift-tools-support-core for this issue.
swiftlang/swift-tools-support-core#506