Adopt utimensat for setting file modification dates (#1324)

Author: jmschonfeld

Sources/FoundationEssentials/FileManager/FileManager+Files.swift

@@ -965,15 +965,15 @@ extension _FileManagerImpl {
 
             if let date = attributes[.modificationDate] as? Date {
                 let (isecs, fsecs) = modf(date.timeIntervalSince1970)
-                if let tv_sec = time_t(exactly: isecs),
-                   let tv_usec = suseconds_t(exactly: round(fsecs * 1000000.0)) {
-                    var timevals = (timeval(), timeval())
-                    timevals.0.tv_sec = tv_sec
-                    timevals.0.tv_usec = tv_usec
-                    timevals.1 = timevals.0
-                    try withUnsafePointer(to: timevals) {
-                        try $0.withMemoryRebound(to: timeval.self, capacity: 2) {
-                            if utimes(fileSystemRepresentation, $0) != 0 {
+                if let tv_sec = Int(exactly: isecs),
+                   let tv_nsec = Int(exactly: round(fsecs * 1000000000.0)) {
+                    var timespecs = (timespec(), timespec())
+                    timespecs.0.tv_sec = tv_sec
+                    timespecs.0.tv_nsec = tv_nsec
+                    timespecs.1 = timespecs.0
+                    try withUnsafePointer(to: timespecs) {
+                        try $0.withMemoryRebound(to: timespec.self, capacity: 2) {
+                            if utimensat(AT_FDCWD, fileSystemRepresentation, $0, 0) != 0 {
                                 throw CocoaError.errorWithFilePath(path, errno: errno, reading: false)
                             }
                         }

Tests/FoundationEssentialsTests/FileManager/FileManagerTests.swift

@@ -793,6 +793,20 @@ final class FileManagerTests : XCTestCase {
         }
     }
 
+    func testRoundtripModificationDate() throws {
+        try FileManagerPlayground {
+            "foo"
+        }.test {
+            // Precision of modification dates is dependent not only on the platform, but on the file system used
+            // Ensure that roundtripping supports at least millisecond-level precision, but some file systems may support more up to nanosecond precision
+            let date = Date(timeIntervalSince1970: 10.003)
+            try $0.setAttributes([.modificationDate : date], ofItemAtPath: "foo")
+            let readValue = try XCTUnwrap($0.attributesOfItem(atPath: "foo")[.modificationDate], "No value provided for file modification date")
+            let readDate = try XCTUnwrap(readValue as? Date, "File modification date was not a date (found type \(type(of: readValue)))")
+            XCTAssertEqual(readDate.timeIntervalSince1970, date.timeIntervalSince1970, accuracy: 0.0005, "File modification date (\(readDate.timeIntervalSince1970)) does not match expected modification date (\(date.timeIntervalSince1970))")
+        }
+    }
+    
     func testImplicitlyConvertibleFileAttributes() throws {
         try FileManagerPlayground {
             File("foo", attributes: [.posixPermissions : UInt16(0o644)])