Make error message when explicitly adding an invalid device more clear.

Before, you would get something like:

`InvalidArgumentError: Cannot assign a device to node 'save/RestoreV2_45': Could not satisfy explicit device specification '/job:ps/task:1/device:CPU:0' because no devices matching that specification are registered in this process; available devices: /job:localhost/replica:0/task:0/cpu:0 [[Node: save/RestoreV2_45 = RestoreV2[dtypes=[DT_FLOAT], _device="/job:ps/task:1/device:CPU:0"](save/Const, save/RestoreV2_45/tensor_names, save/RestoreV2_45/shape_and_slices)]] Caused by op u'save/RestoreV2_45', defined`

And now this reads:

`InvalidArgumentError: Cannot assign a device for operation 'save/RestoreV2_45':
Operation was explicitly assigned to '/job:ps/task:1/device:CPU:0'
but available devices are [ /job:localhost/replica:0/task:0/cpu:0 ]. Make
sure the device specification refers to a valid device.

This drops the additional debug_info because this condition is tightly
scoped to lack of devices, and so node information is unnecessary.
Change: 154379360

tensorflow/core/common_runtime/simple_placer.cc

@@ -341,11 +341,10 @@ class ColocationGraph {
             std::sort(device_names.begin(), device_names.end());
 
             return errors::InvalidArgument(
-                "Could not satisfy explicit device specification '",
-                node->def().device(),
-                "' because no devices matching that specification "
-                "are registered in this process; available devices: ",
-                str_util::Join(device_names, ", "), debug_info);
+                "Operation was explicitly assigned to ", node->def().device(),
+                " but available devices are [ ",
+                str_util::Join(device_names, ", "), " ]. Make sure ",
+                "the device specification refers to a valid device.");
           } else if (specified_device_name.has_type) {
             return errors::InvalidArgument(
                 "Could not satisfy explicit device specification '",
@@ -741,7 +740,7 @@ Status SimplePlacer::Run() {
     status = colocation_graph.GetDevicesForNode(node, &devices);
     if (!status.ok()) {
       return AttachDef(
-          errors::InvalidArgument("Cannot assign a device to node '",
+          errors::InvalidArgument("Cannot assign a device for operation '",
                                   node->name(), "': ", status.error_message()),
           node->def());
     }
@@ -783,7 +782,7 @@ Status SimplePlacer::Run() {
     status = colocation_graph.GetDevicesForNode(node, &devices);
     if (!status.ok()) {
       return AttachDef(
-          errors::InvalidArgument("Cannot assign a device to node '",
+          errors::InvalidArgument("Cannot assign a device for operation '",
                                   node->name(), "': ", status.error_message()),
           node->def());
     }
@@ -801,7 +800,7 @@ Status SimplePlacer::Run() {
             return e->dst()->assigned_device_name() == output_device_name;
           });
 
-      if (consumers_on_same_device && 
+      if (consumers_on_same_device &&
           CanAssignToDevice(output_device_name, devices)) {
         assigned_device = output_device_name;
       }

tensorflow/core/common_runtime/simple_placer_test.cc

@@ -939,10 +939,7 @@ TEST_F(SimplePlacerTest, TestUnknownDevice) {
 
   Status s = Place(&g);
   EXPECT_EQ(error::INVALID_ARGUMENT, s.code());
-  EXPECT_TRUE(
-      StringPiece(s.error_message())
-          .contains(
-              "Could not satisfy explicit device specification '/job:foo'"));
+  EXPECT_TRUE(StringPiece(s.error_message()).contains("/job:foo"));
 }
 
 // Test that placement fails when the combination of partial
@@ -957,10 +954,7 @@ TEST_F(SimplePlacerTest, TestUnknownMergedDevice) {
 
   Status s = Place(&g);
   EXPECT_EQ(error::INVALID_ARGUMENT, s.code());
-  EXPECT_TRUE(
-      StringPiece(s.error_message())
-          .contains(
-              "Could not satisfy explicit device specification '/job:foo'"));
+  EXPECT_TRUE(StringPiece(s.error_message()).contains("/job:foo"));
 }
 
 // Test that placement fails when the previously-assigned device for a
@@ -1107,10 +1101,7 @@ TEST_F(SimplePlacerTest, TestNonexistentGpuNoAllowSoftPlacement) {
   SessionOptions options;
   Status s = Place(&g, &options);
   EXPECT_EQ(error::INVALID_ARGUMENT, s.code());
-  EXPECT_TRUE(StringPiece(s.error_message())
-                  .contains("Could not satisfy explicit "
-                            "device specification "
-                            "'/device:fakegpu:11'"));
+  EXPECT_TRUE(StringPiece(s.error_message()).contains("/device:fakegpu:11"));
 }
 
 // Test that placement fails when a node requests an explicit device that is not
@@ -1127,10 +1118,7 @@ TEST_F(SimplePlacerTest, TestUnsupportedDeviceNoAllowSoftPlacement) {
   SessionOptions options;
   Status s = Place(&g, &options);
   EXPECT_EQ(error::INVALID_ARGUMENT, s.code());
-  EXPECT_TRUE(StringPiece(s.error_message())
-                  .contains("Could not satisfy explicit "
-                            "device specification "
-                            "'/device:fakecpu:0'"));
+  EXPECT_TRUE(StringPiece(s.error_message()).contains("/device:fakecpu:0"));
   EXPECT_TRUE(
       StringPiece(s.error_message())
           .contains("no supported kernel for fakecpu devices is available"));
@@ -1151,12 +1139,9 @@ TEST_F(SimplePlacerTest, TestNonExistentDevice) {
   Status s = Place(&g, &options);
   EXPECT_EQ(error::INVALID_ARGUMENT, s.code());
   LOG(WARNING) << s.error_message();
-  EXPECT_TRUE(
-      StringPiece(s.error_message())
-          .contains("Could not satisfy explicit device specification "
-                    "'/job:foo/replica:17' "
-                    "because no devices matching that specification are "
-                    "registered in this process"));
+  EXPECT_TRUE(StringPiece(s.error_message())
+                  .contains("was explicitly assigned to /job:foo/replica:17 "
+                            "but available devices"));
 }
 
 TEST_F(SimplePlacerTest, TestUnsupportedDeviceAllowSoftPlacement) {

tensorflow/python/framework/test_util_test.py

@@ -252,8 +252,7 @@ class TestUtilTest(test_util.TensorFlowTestCase):
     self.assertArrayNear(a, b, 0.001)
 
   def testForceGPU(self):
-    with self.assertRaisesRegexp(errors.InvalidArgumentError,
-                                 "Cannot assign a device to node"):
+    with self.assertRaises(errors.InvalidArgumentError):
       with self.test_session(force_gpu=True):
         # this relies on us not having a GPU implementation for assert, which
         # seems sensible

tensorflow/python/training/saver_test.py

@@ -1845,8 +1845,8 @@ class MetaGraphTest(test.TestCase):
     with session.Session(graph=ops_lib.Graph()) as sess:
       saver_module.import_meta_graph(
           meta_graph_def, clear_devices=False, import_scope="new_model")
-      with self.assertRaisesRegexp(errors_impl.InvalidArgumentError,
-                                   "Cannot assign a device to node"):
+      # Device refers to GPU, which is not available here.
+      with self.assertRaises(errors_impl.InvalidArgumentError):
         sess.run(variables.global_variables_initializer())
 
     with session.Session(graph=ops_lib.Graph()) as sess: