Add async overloads of withLock for FS I/O (#420)

When converting parts of the SwiftPM codebase from callbacks to `async`/`await` I've stumbled upon uses of file system locking that have to work across an async closure call. This is an additive change and has no impact on the existing blocking non-async uses of `FileLock.withLock`.

Author: MaxDesiatov

Sources/TSCBasic/FileSystem.swift

@@ -288,6 +288,9 @@ public protocol FileSystem: Sendable {
 
     /// Execute the given block while holding the lock.
     func withLock<T>(on path: AbsolutePath, type: FileLock.LockType, _ body: () throws -> T) throws -> T
+
+    /// Execute the given block while holding the lock.
+    func withLock<T>(on path: AbsolutePath, type: FileLock.LockType, _ body: () async throws -> T) async throws -> T
 }
 
 /// Convenience implementations (default arguments aren't permitted in protocol
@@ -336,6 +339,10 @@ public extension FileSystem {
         throw FileSystemError(.unsupported, path)
     }
 
+    func withLock<T>(on path: AbsolutePath, type: FileLock.LockType, _ body: () async throws -> T) async throws -> T {
+        throw FileSystemError(.unsupported, path)
+    }
+
     func hasQuarantineAttribute(_ path: AbsolutePath) -> Bool { false }
 
     func hasAttribute(_ name: FileSystemAttribute, _ path: AbsolutePath) -> Bool { false }
@@ -601,12 +608,20 @@ private struct LocalFileSystem: FileSystem {
     func withLock<T>(on path: AbsolutePath, type: FileLock.LockType = .exclusive, _ body: () throws -> T) throws -> T {
         try FileLock.withLock(fileToLock: path, type: type, body: body)
     }
+
+    func withLock<T>(
+        on path: AbsolutePath,
+        type: FileLock.LockType = .exclusive,
+        _ body: () async throws -> T
+    ) async throws -> T {
+        try await FileLock.withLock(fileToLock: path, type: type, body: body)
+    }
 }
 
 /// Concrete FileSystem implementation which simulates an empty disk.
 public final class InMemoryFileSystem: FileSystem {
     /// Private internal representation of a file system node.
-    /// Not threadsafe.
+    /// Not thread-safe.
     private class Node {
         /// The actual node data.
         let contents: NodeContents
@@ -622,7 +637,7 @@ public final class InMemoryFileSystem: FileSystem {
     }
 
     /// Private internal representation the contents of a file system node.
-    /// Not threadsafe.
+    /// Not thread-safe.
     private enum NodeContents {
         case file(ByteString)
         case directory(DirectoryContents)
@@ -642,7 +657,7 @@ public final class InMemoryFileSystem: FileSystem {
     }
 
     /// Private internal representation the contents of a directory.
-    /// Not threadsafe.
+    /// Not thread-safe.
     private final class DirectoryContents {
         var entries: [String: Node]
 
@@ -697,7 +712,7 @@ public final class InMemoryFileSystem: FileSystem {
     }
 
     /// Private function to look up the node corresponding to a path.
-    /// Not threadsafe.
+    /// Not thread-safe.
     private func getNode(_ path: AbsolutePath, followSymlink: Bool = true) throws -> Node? {
         func getNodeInternal(_ path: AbsolutePath) throws -> Node? {
             // If this is the root node, return it.
@@ -841,7 +856,7 @@ public final class InMemoryFileSystem: FileSystem {
         }
     }
 
-    /// Not threadsafe.
+    /// Not thread-safe.
     private func _createDirectory(_ path: AbsolutePath, recursive: Bool) throws {
         // Ignore if client passes root.
         guard !path.isRoot else {
@@ -989,7 +1004,7 @@ public final class InMemoryFileSystem: FileSystem {
     }
 
     /// Private implementation of core copying function.
-    /// Not threadsafe.
+    /// Not thread-safe.
     private func _copy(from sourcePath: AbsolutePath, to destinationPath: AbsolutePath) throws {
         // Get the source node.
         guard let source = try getNode(sourcePath) else {

Sources/TSCBasic/Lock.swift

@@ -177,8 +177,19 @@ public final class FileLock {
         defer { unlock() }
         return try body()
     }
-    
-    public static func withLock<T>(fileToLock: AbsolutePath, lockFilesDirectory: AbsolutePath? = nil, type: LockType = .exclusive, body: () throws -> T) throws -> T {
+
+    /// Execute the given block while holding the lock.
+    public func withLock<T>(type: LockType = .exclusive, _ body: () async throws -> T) async throws -> T {
+        try lock(type: type)
+        defer { unlock() }
+        return try await body()
+    }
+
+    private static func prepareLock(
+        fileToLock: AbsolutePath,
+        at lockFilesDirectory: AbsolutePath? = nil,
+        _ type: LockType = .exclusive
+    ) throws -> FileLock {
         // unless specified, we use the tempDirectory to store lock files
         let lockFilesDirectory = try lockFilesDirectory ?? localFileSystem.tempDirectory
         if !localFileSystem.exists(lockFilesDirectory) {
@@ -215,7 +226,26 @@ public final class FileLock {
 #endif
         let lockFilePath = lockFilesDirectory.appending(component: lockFileName)
 
-        let lock = FileLock(at: lockFilePath)
+        return FileLock(at: lockFilePath)
+    }
+
+    public static func withLock<T>(
+        fileToLock: AbsolutePath,
+        lockFilesDirectory: AbsolutePath? = nil,
+        type: LockType = .exclusive,
+        body: () throws -> T
+    ) throws -> T {
+        let lock = try Self.prepareLock(fileToLock: fileToLock, at: lockFilesDirectory, type)
         return try lock.withLock(type: type, body)
     }
+
+    public static func withLock<T>(
+        fileToLock: AbsolutePath,
+        lockFilesDirectory: AbsolutePath? = nil,
+        type: LockType = .exclusive,
+        body: () async throws -> T
+    ) async throws -> T {
+        let lock = try Self.prepareLock(fileToLock: fileToLock, at: lockFilesDirectory, type)
+        return try await lock.withLock(type: type, body)
+    }
 }