Accurate Tensor.device for TFEager backends

Sources/TensorFlow/Core/Tensor.swift

@@ -13,6 +13,7 @@
 // limitations under the License.
 
 import CTensorFlow
+import Foundation
 import _Differentiation
 
 infix operator .==: ComparisonPrecedence
@@ -768,7 +769,40 @@ extension Tensor: Differentiable & EuclideanDifferentiable where Scalar: TensorF
         case .XLA:
           return xlaTensor.device
         case .TF_EAGER:
-          return Device.defaultTFEager
+          var kind: Device.Kind = .CPU
+          var ordinal = 0
+          let status = _ExecutionContext.global.status
+
+          // Find out what the underlying libraries think the default is.
+          if let cString = TFE_TensorHandleDeviceName(handle._cTensorHandle, status) {
+            checkOk(status)
+            let tfDeviceName = String(cString: cString)
+
+            // Parse type and ordinal from a string with the expected syntax:
+            //   /job:localhost/replica:0/task:0/device:CPU:0
+            let pattern = ".+device:(.+):(\\d+)$"
+            let regex = try! NSRegularExpression(pattern: pattern)
+            let nsrange = NSRange(tfDeviceName.startIndex..., in: tfDeviceName)
+            if let match = regex.firstMatch(in: tfDeviceName, range: nsrange) {
+              if let kindRange = Range(match.range(at: 1), in: tfDeviceName) {
+                switch String(tfDeviceName[kindRange]).uppercased() {
+                case "CPU":
+                  kind = .CPU
+                case "GPU":
+                  kind = .GPU
+                case "TPU":
+                  kind = .TPU
+                default:
+                  kind = .CPU
+                }
+              }
+              if let ordinalRange = Range(match.range(at: 2), in: tfDeviceName) {
+                ordinal = Int(tfDeviceName[ordinalRange]) ?? 0
+              }
+            }
+          }
+
+          return Device(kind: kind, ordinal: ordinal, backend: .TF_EAGER)
         }
       }
     }