Fixes for Sequential model with multiple inputs.

- While `Sequential` works with multiple inputs in most scenarios, `build()` did not allow building with multiple inputs. This is now fixed.
- Removed the `build_input_shape` from the new serialization format. This is a legacy concept, which has been replaced with `build_config.input_shape` in the new format. Having both could cause models to be built twice.
- `build_from_config` now always call `build` with `TensorShape`s, not tuples. Not all layers handle tuples correctly.

PiperOrigin-RevId: 716010092

tf_keras/engine/base_layer.py

@@ -2321,7 +2321,7 @@ def build_from_config(self, config):
         """
         input_shape = config["input_shape"]
         if input_shape is not None:
-            self.build(input_shape)
+            self.build(tf_utils.convert_shapes(input_shape, to_tuples=False))
 
     ############################################################################
     # Methods & attributes below are all private and only used by the framework.

tf_keras/engine/sequential.py

@@ -285,12 +285,16 @@ def _build_graph_network_for_inferred_shape(
         ):
             # Determine whether the input shape is novel, i.e. whether the model
             # should be rebuilt.
-            input_shape = tuple(input_shape)
+            input_shape = tf_utils.convert_shapes(input_shape)
             if self._inferred_input_shape is None:
                 new_shape = input_shape
             else:
-                new_shape = relax_input_shape(
-                    self._inferred_input_shape, input_shape
+                new_shape = tf.nest.map_structure(
+                    _relax_input_shape,
+                    tf_utils.convert_shapes(
+                        self._inferred_input_shape, to_tuples=False
+                    ),
+                    tf_utils.convert_shapes(input_shape, to_tuples=False),
                 )
             if (
                 new_shape is not None
@@ -299,10 +303,13 @@ def _build_graph_network_for_inferred_shape(
                 # A novel shape has been received: we need to rebuild the model.
                 # In case we are inside a graph function, we step out of it.
                 with tf.init_scope():
-                    inputs = input_layer.Input(
-                        batch_shape=new_shape,
-                        dtype=input_dtype,
-                        name=self.layers[0].name + "_input",
+                    inputs = tf.nest.map_structure(
+                        lambda s: input_layer.Input(
+                            batch_shape=tf_utils.convert_shapes(s),
+                            dtype=input_dtype,
+                            name=self.layers[0].name + "_input",
+                        ),
+                        tf_utils.convert_shapes(new_shape, to_tuples=False),
                     )
                     layer_input = inputs
                     created_nodes = set()
@@ -370,7 +377,7 @@ def build(self, input_shape=None):
                 raise ValueError("You must provide an `input_shape` argument.")
             self._build_graph_network_for_inferred_shape(input_shape)
             if not self.built:
-                input_shape = tuple(input_shape)
+                input_shape = tf_utils.convert_shapes(input_shape)
                 self._build_input_shape = input_shape
                 super().build(input_shape)
         self.built = True
@@ -435,7 +442,8 @@ def compute_mask(self, inputs, mask):
     def get_config(self):
         layer_configs = []
         serialize_obj_fn = serialization_lib.serialize_keras_object
-        if getattr(self, "use_legacy_config", None):
+        use_legacy_config = getattr(self, "use_legacy_config", False)
+        if use_legacy_config:
             serialize_obj_fn = legacy_serialization.serialize_keras_object
         for layer in super().layers:
             # `super().layers` include the InputLayer if available (it is
@@ -446,7 +454,11 @@ def get_config(self):
         config = training.Model.get_config(self)
         config["name"] = self.name
         config["layers"] = copy.deepcopy(layer_configs)
-        if not self._is_graph_network and self._build_input_shape is not None:
+        if (
+            use_legacy_config
+            and not self._is_graph_network
+            and self._build_input_shape
+        ):
             config["build_input_shape"] = self._build_input_shape
         return config
 
@@ -458,6 +470,7 @@ def from_config(cls, config, custom_objects=None):
             layer_configs = config["layers"]
         else:
             name = None
+            build_input_shape = None
             layer_configs = config
         model = cls(name=name)
         for layer_config in layer_configs:
@@ -519,11 +532,15 @@ def _get_shape_tuple(t):
     return None
 
 
-def relax_input_shape(shape_1, shape_2):
+def _relax_input_shape(shape_1, shape_2):
     if shape_1 is None or shape_2 is None:
         return None
-    if len(shape_1) != len(shape_2):
+    if shape_1.rank is None or shape_2.rank is None:
+        return None
+    if shape_1.rank != shape_2.rank:
         return None
+    shape_1 = shape_1.as_list()
+    shape_2 = shape_2.as_list()
     return tuple(None if d1 != d2 else d1 for d1, d2 in zip(shape_1, shape_2))
 
 

tf_keras/engine/sequential_test.py

@@ -19,6 +19,7 @@
 from absl.testing import parameterized
 
 import tf_keras as keras
+from tf_keras.saving import object_registration
 from tf_keras.testing_infra import test_combinations
 from tf_keras.testing_infra import test_utils
 
@@ -574,6 +575,22 @@ def test_multi_inputs_outputs(self):
         model(image_inputs)
         model.fit(x=image_inputs, y=image_inputs, steps_per_epoch=1)
 
+    @test_combinations.run_all_keras_modes(always_skip_v1=True)
+    def test_multi_inputs_build(self):
+        model = keras.Sequential([ImageMultiplyLayer()])
+        model.build({"images": (None, 512, 512, 3), "weights": (None, 3)})
+
+        image_inputs = tf.ones((2, 512, 512, 3))
+        weight_inputs = tf.ones((2, 3))
+        output = model({"images": image_inputs, "weights": weight_inputs})
+
+        config = model.to_json()
+        new_model = keras.models.model_from_json(config)
+        new_output = new_model(
+                {"images": image_inputs, "weights": weight_inputs}
+        )
+        self.assertAllClose(output, new_output)
+
 
 class TestSequentialEagerIntegration(test_combinations.TestCase):
     @test_combinations.run_all_keras_modes
@@ -642,10 +659,20 @@ def test_build_empty_network(self):
         self.assertTrue(model.built)
 
 
+@object_registration.register_keras_serializable()
 class ImageAugmentLayer(keras.layers.Layer):
     def call(self, inputs):
         return inputs
 
 
+@object_registration.register_keras_serializable()
+class ImageMultiplyLayer(keras.layers.Layer):
+    def call(self, inputs):
+        images = inputs["images"]
+        weights = inputs["weights"]
+        images = tf.reshape(images, (-1, 1, 1, 3))
+        return images * weights
+
+
 if __name__ == "__main__":
     tf.test.main()