Make Configuration.workingDirectory optional

jakepetroules · jakepetroules · commit 75573f9bc1b0 · 2025-06-13T11:47:16.000-07:00
On all platforms, retrieving the current working directory is a failable operation. When a Configuration is given a null working directory, instead of resolving that to the current working directory at initialization time (which can't be done safely because Configuration.init is non-failable), make Configuration.workingDirectory optional and preserve any nil input through to process creation time. Both CreateProcess (Windows) and posix_spawn or fork/exec (POSIX) inherit the working directory of the calling process if it is not specified, so this doesn't change any behavior.

It also better matches the design of other properties on the Configuration struct like the Executable, which defer resolution of their concrete value rather than doing so at Configuration.init time.

Lastly, it removes incorrect code: the implementation of FilePath.currentWorkingDirectory could crash on POSIX platforms if the current directory was no longer accessible or getcwd failed for any other reason, and on Windows it would not properly support non-ASCII characters in path names nor path names longer than 260 characters.
diff --git a/Sources/Subprocess/Configuration.swift b/Sources/Subprocess/Configuration.swift
@@ -39,7 +39,8 @@ public struct Configuration: Sendable {
     /// The environment to use when running the executable.
     public var environment: Environment
     /// The working directory to use when running the executable.
-    public var workingDirectory: FilePath
+    /// If this property is `nil`, the subprocess will inherit the working directory from the parent process.
+    public var workingDirectory: FilePath?
     /// The platform specific options to use when
     /// running the subprocess.
     public var platformOptions: PlatformOptions
@@ -54,7 +55,7 @@ public struct Configuration: Sendable {
         self.executable = executable
         self.arguments = arguments
         self.environment = environment
-        self.workingDirectory = workingDirectory ?? .currentWorkingDirectory
+        self.workingDirectory = workingDirectory
         self.platformOptions = platformOptions
     }
 
@@ -107,7 +108,7 @@ extension Configuration: CustomStringConvertible, CustomDebugStringConvertible {
                 executable: \(self.executable.description),
                 arguments: \(self.arguments.description),
                 environment: \(self.environment.description),
-                workingDirectory: \(self.workingDirectory),
+                workingDirectory: \(self.workingDirectory?.string ?? ""),
                 platformOptions: \(self.platformOptions.description(withIndent: 1))
             )
             """
@@ -119,7 +120,7 @@ extension Configuration: CustomStringConvertible, CustomDebugStringConvertible {
                 executable: \(self.executable.debugDescription),
                 arguments: \(self.arguments.debugDescription),
                 environment: \(self.environment.debugDescription),
-                workingDirectory: \(self.workingDirectory),
+                workingDirectory: \(self.workingDirectory?.string ?? ""),
                 platformOptions: \(self.platformOptions.description(withIndent: 1))
             )
             """
@@ -714,14 +715,6 @@ internal struct CreatedPipe: ~Copyable {
     }
 }
 
-extension FilePath {
-    static var currentWorkingDirectory: Self {
-        let path = getcwd(nil, 0)!
-        defer { free(path) }
-        return .init(String(cString: path))
-    }
-}
-
 extension Optional where Wrapped: Collection {
     func withOptionalUnsafeBufferPointer<Result>(
         _ body: ((UnsafeBufferPointer<Wrapped.Element>)?) throws -> Result
diff --git a/Sources/Subprocess/Platforms/Subprocess+Darwin.swift b/Sources/Subprocess/Platforms/Subprocess+Darwin.swift
@@ -349,9 +349,13 @@ extension Configuration {
                 }
 
                 // Setup cwd
-                let intendedWorkingDir = self.workingDirectory.string
-                let chdirError: Int32 = intendedWorkingDir.withPlatformString { workDir in
-                    return posix_spawn_file_actions_addchdir_np(&fileActions, workDir)
+                let chdirError: Int32
+                if let intendedWorkingDir = self.workingDirectory?.string {
+                    chdirError = intendedWorkingDir.withPlatformString { workDir in
+                        return posix_spawn_file_actions_addchdir_np(&fileActions, workDir)
+                    }
+                } else {
+                    chdirError = 0
                 }
 
                 // Error handling
@@ -457,12 +461,13 @@ extension Configuration {
                 errorRead: errorReadFileDescriptor,
                 errorWrite: errorWriteFileDescriptor
             )
-            let workingDirectory = self.workingDirectory.string
-            guard Configuration.pathAccessible(workingDirectory, mode: F_OK) else {
-                throw SubprocessError(
-                    code: .init(.failedToChangeWorkingDirectory(workingDirectory)),
-                    underlyingError: .init(rawValue: ENOENT)
-                )
+            if let workingDirectory = self.workingDirectory?.string {
+                guard Configuration.pathAccessible(workingDirectory, mode: F_OK) else {
+                    throw SubprocessError(
+                        code: .init(.failedToChangeWorkingDirectory(workingDirectory)),
+                        underlyingError: .init(rawValue: ENOENT)
+                    )
+                }
             }
             throw SubprocessError(
                 code: .init(.executableNotFound(self.executable.description)),
diff --git a/Sources/Subprocess/Platforms/Subprocess+Linux.swift b/Sources/Subprocess/Platforms/Subprocess+Linux.swift
@@ -85,11 +85,10 @@ extension Configuration {
                     errorReadFileDescriptor?.platformDescriptor() ?? -1,
                 ]
 
-                let workingDirectory: String = self.workingDirectory.string
                 // Spawn
                 var pid: pid_t = 0
                 let spawnError: CInt = possibleExecutablePath.withCString { exePath in
-                    return workingDirectory.withCString { workingDir in
+                    return (self.workingDirectory?.string).withOptionalCString { workingDir in
                         return supplementaryGroups.withOptionalUnsafeBufferPointer { sgroups in
                             return fileDescriptors.withUnsafeBufferPointer { fds in
                                 return _subprocess_fork_exec(
@@ -173,12 +172,13 @@ extension Configuration {
                 errorRead: errorReadFileDescriptor,
                 errorWrite: errorWriteFileDescriptor
             )
-            let workingDirectory = self.workingDirectory.string
-            guard Configuration.pathAccessible(workingDirectory, mode: F_OK) else {
-                throw SubprocessError(
-                    code: .init(.failedToChangeWorkingDirectory(workingDirectory)),
-                    underlyingError: .init(rawValue: ENOENT)
-                )
+            if let workingDirectory = self.workingDirectory?.string {
+                guard Configuration.pathAccessible(workingDirectory, mode: F_OK) else {
+                    throw SubprocessError(
+                        code: .init(.failedToChangeWorkingDirectory(workingDirectory)),
+                        underlyingError: .init(rawValue: ENOENT)
+                    )
+                }
             }
             throw SubprocessError(
                 code: .init(.executableNotFound(self.executable.description)),
diff --git a/Sources/Subprocess/Platforms/Subprocess+Windows.swift b/Sources/Subprocess/Platforms/Subprocess+Windows.swift
@@ -84,7 +84,7 @@ extension Configuration {
                 try environment.withCString(
                     encodedAs: UTF16.self
                 ) { environmentW in
-                    try intendedWorkingDir.withNTPathRepresentation { intendedWorkingDirW in
+                    try intendedWorkingDir.withOptionalNTPathRepresentation { intendedWorkingDirW in
                         let created = CreateProcessW(
                             applicationNameW,
                             UnsafeMutablePointer<WCHAR>(mutating: commandAndArgsW),
@@ -223,7 +223,7 @@ extension Configuration {
                             try environment.withCString(
                                 encodedAs: UTF16.self
                             ) { environmentW in
-                                try intendedWorkingDir.withNTPathRepresentation { intendedWorkingDirW in
+                                try intendedWorkingDir.withOptionalNTPathRepresentation { intendedWorkingDirW in
                                     let created = CreateProcessWithLogonW(
                                         usernameW,
                                         domainW,
@@ -769,7 +769,7 @@ extension Configuration {
         applicationName: String?,
         commandAndArgs: String,
         environment: String,
-        intendedWorkingDir: String
+        intendedWorkingDir: String?
     ) {
         // Prepare environment
         var env: [String: String] = [:]
@@ -806,19 +806,21 @@ extension Configuration {
             commandAndArgs
         ) = try self.generateWindowsCommandAndAgruments()
         // Validate workingDir
-        guard Self.pathAccessible(self.workingDirectory.string) else {
-            throw SubprocessError(
-                code: .init(
-                    .failedToChangeWorkingDirectory(self.workingDirectory.string)
-                ),
-                underlyingError: nil
-            )
+        if let workingDirectory = self.workingDirectory?.string {
+            guard Self.pathAccessible(workingDirectory) else {
+                throw SubprocessError(
+                    code: .init(
+                        .failedToChangeWorkingDirectory(workingDirectory)
+                    ),
+                    underlyingError: nil
+                )
+            }
         }
         return (
             applicationName: applicationName,
             commandAndArgs: commandAndArgs,
             environment: environmentString,
-            intendedWorkingDir: self.workingDirectory.string
+            intendedWorkingDir: self.workingDirectory?.string
         )
     }
 
diff --git a/Sources/_SubprocessCShims/process_shims.c b/Sources/_SubprocessCShims/process_shims.c
@@ -397,9 +397,11 @@ static int _subprocess_posix_spawn_fallback(
         if (rc != 0) { return rc; }
     }
     // Setup working directory
-    rc = _subprocess_addchdir_np(&file_actions, working_directory);
-    if (rc != 0) {
-        return rc;
+    if (working_directory != NULL) {
+        rc = _subprocess_addchdir_np(&file_actions, working_directory);
+        if (rc != 0) {
+            return rc;
+        }
     }
 
     // Close parent side

Original file line number	Diff line number	Diff line change
`@@ -397,9 +397,11 @@ static int _subprocess_posix_spawn_fallback(`
`397`	`397`	`if (rc != 0) { return rc; }`
`398`	`398`	`}`
`399`	`399`	`// Setup working directory`
`400`		`- rc = _subprocess_addchdir_np(&file_actions, working_directory);`
`401`		`- if (rc != 0) {`
`402`		`- return rc;`
	`400`	`+ if (working_directory != NULL) {`
	`401`	`+ rc = _subprocess_addchdir_np(&file_actions, working_directory);`
	`402`	`+ if (rc != 0) {`
	`403`	`+ return rc;`
	`404`	`+ }`
`403`	`405`	`}`
`404`	`406`
`405`	`407`	`// Close parent side`