[gpt2pre 3] Preprocessor Layer (#7794)

* Add Preprocessor layer

* Remove uneeded args

* Use LayerArgs

* Remove import from src

* Add fromConfig method

* Serialize tokenizer properly

* Add test cases for preprocessor

* Preprocessor tests with no set tokenizer

---------

Co-authored-by: Linchenn <40653845+Linchenn@users.noreply.github.com>

tfjs-layers/src/layers/nlp/models/preprocessor.ts

@@ -0,0 +1,76 @@
+/**
+ * @license
+ * Copyright 2023 Google LLC.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * =============================================================================
+ */
+
+/* Original source: keras-nlp/models/preprocessor.py */
+import { serialization } from '@tensorflow/tfjs-core';
+
+import { Layer, LayerArgs } from '../../../engine/topology';
+import { Tokenizer } from '../tokenizers';
+import { Kwargs } from '../../../types';
+import { deserializeKerasObject, serializeKerasObject } from '../../../utils/generic_utils';
+
+/**
+ * Base class for model Preprocessors.
+ */
+export class Preprocessor extends Layer {
+  /** @nocollapse */
+  static readonly className = 'Preprocessor';
+
+  private _tokenizer: Tokenizer;
+
+  constructor(args: LayerArgs) {
+    super(args);
+  }
+
+  /**
+   * The tokenizer used to tokenize strings.
+   */
+  get tokenizer() {
+    return this._tokenizer;
+  }
+
+  set tokenizer(value: Tokenizer) {
+    this._tokenizer = value;
+  }
+
+  override getConfig(): serialization.ConfigDict {
+    const config = super.getConfig();
+    config.tokenizer = serializeKerasObject(this.tokenizer);
+    return config;
+  }
+
+  static override fromConfig<T extends serialization.Serializable>(
+    cls: serialization.SerializableConstructor<T>,
+    config: serialization.ConfigDict
+  ): T {
+    const kwargs: Kwargs = config;
+
+    if (config.tokenizer != null && !(config.tokenizer instanceof Tokenizer)) {
+      const tokenizerConfigDict = config.tokenizer as serialization.ConfigDict;
+
+      kwargs.tokenizer = deserializeKerasObject(
+        tokenizerConfigDict,
+        serialization.SerializationMap.getMap().classNameMap,
+        {}, 'preprocessor');
+    }
+    return new cls(kwargs);
+  }
+
+  static tokenizerCls<T extends serialization.Serializable>(
+    cls: serialization.SerializableConstructor<T>) {}
+}
+serialization.registerClass(Preprocessor);

tfjs-layers/src/layers/nlp/models/preprocessor_test.ts

@@ -0,0 +1,35 @@
+/**
+ * @license
+ * Copyright 2023 Google LLC.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * =============================================================================
+ */
+
+/**
+ * Unit Tests for Preprocessor Layers.
+ */
+import { Preprocessor } from './preprocessor';
+
+describe('Preprocessor', () => {
+  let preprocessor: Preprocessor;
+
+  beforeEach(() => {
+    preprocessor = new Preprocessor({});
+  });
+
+  it('serialization round-trip with no set tokenizer', () => {
+    const reserialized = Preprocessor.fromConfig(
+      Preprocessor, preprocessor.getConfig());
+    expect(reserialized.getConfig()).toEqual(preprocessor.getConfig());
+  });
+});

tfjs-layers/src/layers/nlp/tokenizers.ts

@@ -331,7 +331,7 @@ export class BytePairTokenizer extends Tokenizer {
 
   override getConfig(): serialization.ConfigDict {
     const config = {
-      vocabulary: this.vocabulary,
+      vocabulary: Array.from(this._vocabulary.entries()),
       merges: this.merges,
       sequenceLength: this.sequenceLength,
       addPrefixSpace: this.addPrefixSpace,