Fix access time updates changing modification time

Sources/tart/URL+AccessDate.swift

@@ -8,21 +8,21 @@ extension URL {
   }
 
   func updateAccessDate(_ accessDate: Date = Date()) throws {
-    let attrs = try resourceValues(forKeys: [.contentAccessDateKey])
-    let modificationDate = attrs.contentAccessDate!
-
-    let times = [accessDate.asTimeval(), modificationDate.asTimeval()]
-    let ret = utimes(path, times)
+    let times = [accessDate.asTimespec(), timespec(tv_sec: 0, tv_nsec: Int(UTIME_OMIT))]
+    let ret = utimensat(AT_FDCWD, path, times, 0)
     if ret != 0 {
       let details = Errno(rawValue: CInt(errno))
 
-      throw RuntimeError.FailedToUpdateAccessDate("utimes(2) failed: \(details)")
+      throw RuntimeError.FailedToUpdateAccessDate("utimensat(2) failed: \(details)")
     }
   }
 }
 
 extension Date {
-  func asTimeval() -> timeval {
-    timeval(tv_sec: Int(timeIntervalSince1970), tv_usec: 0)
+  func asTimespec() -> timespec {
+    let seconds = floor(timeIntervalSince1970)
+    let nanoseconds = (timeIntervalSince1970 - seconds) * 1_000_000_000
+
+    return timespec(tv_sec: Int(seconds), tv_nsec: Int(nanoseconds))
   }
 }

Tests/TartTests/URLAccessDateTests.swift

@@ -2,21 +2,29 @@ import XCTest
 @testable import tart
 
 final class URLAccessDateTests: XCTestCase {
-  func testGetAndSetAccessTime() throws {
+  func testUpdateAccessDatePreservesModificationDate() throws {
     // Create a temporary file
     let tmpDir = URL(fileURLWithPath: NSTemporaryDirectory(), isDirectory: true)
     var tmpFile = tmpDir.appendingPathComponent(UUID().uuidString)
     FileManager.default.createFile(atPath: tmpFile.path, contents: nil)
+    defer { try? FileManager.default.removeItem(at: tmpFile) }
 
-    // Ensure it's access date is different than our desired access date
-    let arbitraryDate = Date.init(year: 2008, month: 09, day: 28, hour: 23, minute: 15)
-    XCTAssertNotEqual(arbitraryDate, try tmpFile.accessDate())
+    // Ensure its access date is different from our desired access date
+    let accessDate = Date.init(year: 2008, month: 09, day: 28, hour: 23, minute: 15)
+    let modificationDate = Date(timeIntervalSince1970: 1_577_836_800.125)
+    try FileManager.default.setAttributes([.modificationDate: modificationDate], ofItemAtPath: tmpFile.path)
+    XCTAssertNotEqual(accessDate, try tmpFile.accessDate())
 
     // Set our desired access date for a file
-    try tmpFile.updateAccessDate(arbitraryDate)
+    try tmpFile.updateAccessDate(accessDate)
 
     // Ensure the access date has changed to our value
     tmpFile.removeCachedResourceValue(forKey: .contentAccessDateKey)
-    XCTAssertEqual(arbitraryDate, try tmpFile.accessDate())
+    XCTAssertEqual(accessDate, try tmpFile.accessDate())
+
+    // Ensure the modification date has not changed
+    tmpFile.removeCachedResourceValue(forKey: .contentModificationDateKey)
+    let attrs = try tmpFile.resourceValues(forKeys: [.contentModificationDateKey])
+    XCTAssertEqual(modificationDate, try XCTUnwrap(attrs.contentModificationDate))
   }
 }