Add tf.saved_model.Asset public symbol.

`Asset` is the mechanism that allows to make hermetic SavedModels
that depend on files. It replaces functionality that on TF-1.x was
typically provided by the ASSET_FILEPATHS collection.

PiperOrigin-RevId: 267534289

tensorflow/python/compiler/tensorrt/trt_convert.py

@@ -750,7 +750,7 @@ class _TRTEngineResource(tracking.TrackableResource):
     self._resource_name = resource_name
     # Track the serialized engine file in the SavedModel.
     self._filename = self._track_trackable(
-        tracking.TrackableAsset(filename), "_serialized_trt_resource_filename")
+        tracking.Asset(filename), "_serialized_trt_resource_filename")
     self._maximum_cached_engines = maximum_cached_engines
 
   def _create_resource(self):

tensorflow/python/ops/lookup_ops.py

@@ -627,7 +627,7 @@ class TextFileInitializer(TableInitializerBase):
     self._delimiter = delimiter
     self._name = name
     self._filename = self._track_trackable(
-        trackable.TrackableAsset(filename), "_filename")
+        trackable.Asset(filename), "_filename")
 
     super(TextFileInitializer, self).__init__(key_dtype, value_dtype)
 

tensorflow/python/saved_model/load.py

@@ -206,7 +206,7 @@ class Loader(object):
         return obj
       elif resource_variable_ops.is_resource_variable(obj):
         return obj.handle
-      elif isinstance(obj, tracking.TrackableAsset):
+      elif isinstance(obj, tracking.Asset):
         return obj.asset_path
       elif tensor_util.is_tensor(obj):
         return obj
@@ -343,7 +343,7 @@ class Loader(object):
     filename = os.path.join(
         saved_model_utils.get_assets_dir(self._export_dir),
         self._asset_file_def[proto.asset_file_def_index].filename)
-    return tracking.TrackableAsset(filename), setattr
+    return tracking.Asset(filename), setattr
 
   def _recreate_function(self, proto):
     return function_deserialization.recreate_function(

tensorflow/python/saved_model/load_test.py

@@ -204,8 +204,8 @@ class LoadTest(test.TestCase, parameterized.TestCase):
     file2 = self._make_asset("contents 2")
 
     root = tracking.AutoTrackable()
-    root.asset1 = tracking.TrackableAsset(file1)
+    root.asset1 = tracking.Asset(file1)
-    root.asset2 = tracking.TrackableAsset(file2)
+    root.asset2 = tracking.Asset(file2)
 
     save_dir = os.path.join(self.get_temp_dir(), "save_dir")
     save.save(root, save_dir)
@@ -253,7 +253,7 @@ class LoadTest(test.TestCase, parameterized.TestCase):
 
   def test_capture_assets(self, cycles):
     root = tracking.AutoTrackable()
-    root.vocab = tracking.TrackableAsset(self._make_asset("contents"))
+    root.vocab = tracking.Asset(self._make_asset("contents"))
     root.f = def_function.function(
         lambda: root.vocab.asset_path,
         input_signature=[])
@@ -266,7 +266,7 @@ class LoadTest(test.TestCase, parameterized.TestCase):
 
   def test_capture_assets_in_graph(self, cycles):
     root = tracking.AutoTrackable()
-    root.vocab = tracking.TrackableAsset(self._make_asset("contents"))
+    root.vocab = tracking.Asset(self._make_asset("contents"))
     root.f = def_function.function(
         lambda: root.vocab.asset_path,
         input_signature=[])
@@ -290,8 +290,8 @@ class LoadTest(test.TestCase, parameterized.TestCase):
   def test_dedup_assets(self, cycles):
     vocab = self._make_asset("contents")
     root = tracking.AutoTrackable()
-    root.asset1 = tracking.TrackableAsset(vocab)
+    root.asset1 = tracking.Asset(vocab)
-    root.asset2 = tracking.TrackableAsset(vocab)
+    root.asset2 = tracking.Asset(vocab)
     imported = cycle(root, cycles)
     self.assertEqual(imported.asset1.asset_path.numpy(),
                      imported.asset2.asset_path.numpy())

tensorflow/python/saved_model/load_v1_in_v2.py

@@ -201,7 +201,7 @@ class _EagerSavedModelLoader(loader_impl.SavedModelLoader):
     for tensor_name, value in loader_impl.get_asset_tensors(
         self._export_dir, meta_graph_def).items():
       asset_feed_tensors.append(wrapped.graph.as_graph_element(tensor_name))
-      asset_paths.append(tracking.TrackableAsset(value))
+      asset_paths.append(tracking.Asset(value))
     init_fn = wrapped.prune(
         feeds=asset_feed_tensors,
         fetches=[init_anchor, wrapped.graph.as_graph_element(init_op)])

tensorflow/python/saved_model/save.py

@@ -270,7 +270,7 @@ class _SaveableView(object):
         object_map[obj] = new_variable
         resource_map[obj.handle] = new_variable.handle
         self.captured_tensor_node_ids[obj.handle] = node_id
-      elif isinstance(obj, tracking.TrackableAsset):
+      elif isinstance(obj, tracking.Asset):
         _process_asset(obj, asset_info, resource_map)
         self.captured_tensor_node_ids[obj.asset_path] = node_id
 
@@ -498,7 +498,7 @@ _AssetInfo = collections.namedtuple(
         "asset_initializers_by_resource",
         # Map from base asset filenames to full paths
         "asset_filename_map",
-        # Map from TrackableAsset to index of corresponding AssetFileDef
+        # Map from Asset to index of corresponding AssetFileDef
         "asset_index"])
 
 
@@ -662,7 +662,7 @@ def _serialize_object_graph(saveable_view, asset_file_def_index):
 
 def _write_object_proto(obj, proto, asset_file_def_index):
   """Saves an object into SavedObject proto."""
-  if isinstance(obj, tracking.TrackableAsset):
+  if isinstance(obj, tracking.Asset):
     proto.asset.SetInParent()
     proto.asset.asset_file_def_index = asset_file_def_index[obj]
   elif resource_variable_ops.is_resource_variable(obj):

tensorflow/python/saved_model/save_test.py

@@ -426,7 +426,7 @@ class AssetTests(test.TestCase):
 
   def test_asset_path_returned(self):
     root = tracking.AutoTrackable()
-    root.path = tracking.TrackableAsset(self._vocab_path)
+    root.path = tracking.Asset(self._vocab_path)
     save_dir = os.path.join(self.get_temp_dir(), "saved_model")
     root.get_asset = def_function.function(lambda: root.path.asset_path)
     save.save(root, save_dir, signatures=root.get_asset.get_concrete_function())
@@ -469,7 +469,7 @@ class AssetTests(test.TestCase):
     root.f = def_function.function(
         lambda x: 2. * x,
         input_signature=[tensor_spec.TensorSpec(None, dtypes.float32)])
-    root.asset = tracking.TrackableAsset(self._vocab_path)
+    root.asset = tracking.Asset(self._vocab_path)
 
     export_dir = os.path.join(self.get_temp_dir(), "save_dir")
     save.save(root, export_dir)

tensorflow/python/training/tracking/tracking.py

@@ -28,6 +28,7 @@ from tensorflow.python.framework import ops
 from tensorflow.python.training.tracking import base
 from tensorflow.python.training.tracking import data_structures
 from tensorflow.python.util import tf_contextlib
+from tensorflow.python.util.tf_export import tf_export
 
 
 # global _RESOURCE_TRACKER_STACK
@@ -275,8 +276,44 @@ class TrackableResource(CapturableResource):
     super(TrackableResource, self).__init__(device=device, deleter=deleter)
 
 
-class TrackableAsset(base.Trackable):
+@tf_export("saved_model.Asset")
-  """Base class for asset files which need to be tracked."""
+class Asset(base.Trackable):
+  """Represents a file asset to hermetically include in a SavedModel.
+
+  A SavedModel can include arbitrary files, called assets, that are needed
+  for its use. For example a vocabulary file used initialize a lookup table.
+
+  When a trackable object is exported via `tf.saved_model.save()`, all the
+  `Asset`s reachable from it are copied into the SavedModel assets directory.
+  Upon loading, the assets and the serialized functions that depend on them
+  will refer to the correct filepaths inside the SavedModel directory.
+
+  Example:
+
+  ```
+  filename = tf.saved_model.Asset("file.txt")
+
+  @tf.function(input_signature=[])
+  def func():
+    return tf.io.read_file(filename)
+
+  trackable_obj = tf.train.Checkpoint()
+  trackable_obj.func = func
+  trackable_obj.filename = filename
+  tf.saved_model.save(trackable_obj, "/tmp/saved_model")
+
+  # The created SavedModel is hermetic, it does not depend on
+  # the original file and can be moved to another path.
+  tf.io.gfile.remove("file.txt")
+  tf.io.gfile.rename("/tmp/saved_model", "/tmp/new_location")
+
+  reloaded_obj = tf.saved_model.load("/tmp/new_location")
+  print(reloaded_obj.func())
+  ```
+
+  Attributes:
+    asset_path: A 0-D `tf.string` tensor with path to the asset.
+  """
 
   def __init__(self, path):
     """Record the full path to the asset."""
@@ -389,5 +426,5 @@ def cached_per_instance(f):
 
 
 ops.register_tensor_conversion_function(
-    TrackableAsset,
+    Asset,
     lambda asset, **kw: ops.internal_convert_to_tensor(asset.asset_path, **kw))

tensorflow/tools/api/golden/v1/tensorflow.saved_model.-asset.pbtxt

@@ -0,0 +1,14 @@
+path: "tensorflow.saved_model.Asset"
+tf_class {
+  is_instance: "<class \'tensorflow.python.training.tracking.tracking.Asset\'>"
+  is_instance: "<class \'tensorflow.python.training.tracking.base.Trackable\'>"
+  is_instance: "<type \'object\'>"
+  member {
+    name: "asset_path"
+    mtype: "<type \'property\'>"
+  }
+  member_method {
+    name: "__init__"
+    argspec: "args=[\'self\', \'path\'], varargs=None, keywords=None, defaults=None"
+  }
+}

tensorflow/tools/api/golden/v1/tensorflow.saved_model.pbtxt

@@ -8,6 +8,10 @@ tf_module {
     name: "ASSETS_KEY"
     mtype: "<type \'str\'>"
   }
+  member {
+    name: "Asset"
+    mtype: "<type \'type\'>"
+  }
   member {
     name: "Builder"
     mtype: "<type \'type\'>"

tensorflow/tools/api/golden/v2/tensorflow.saved_model.-asset.pbtxt

@@ -0,0 +1,14 @@
+path: "tensorflow.saved_model.Asset"
+tf_class {
+  is_instance: "<class \'tensorflow.python.training.tracking.tracking.Asset\'>"
+  is_instance: "<class \'tensorflow.python.training.tracking.base.Trackable\'>"
+  is_instance: "<type \'object\'>"
+  member {
+    name: "asset_path"
+    mtype: "<type \'property\'>"
+  }
+  member_method {
+    name: "__init__"
+    argspec: "args=[\'self\', \'path\'], varargs=None, keywords=None, defaults=None"
+  }
+}

tensorflow/tools/api/golden/v2/tensorflow.saved_model.pbtxt

@@ -8,6 +8,10 @@ tf_module {
     name: "ASSETS_KEY"
     mtype: "<type \'str\'>"
   }
+  member {
+    name: "Asset"
+    mtype: "<type \'type\'>"
+  }
   member {
     name: "CLASSIFY_INPUTS"
     mtype: "<type \'str\'>"