Copy code from Bert to Roberta and add safeguard script (#7219)

* Copy code from Bert to Roberta and add safeguard script

* Fix docstring

* Comment code

* Formatting

* Update src/transformers/modeling_roberta.py

Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

* Add test and fix bugs

* Fix style and make new comand

Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

tests/test_utils_check_copies.py

@@ -0,0 +1,104 @@
+import os
+import re
+import shutil
+import sys
+import tempfile
+import unittest
+
+
+git_repo_path = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
+sys.path.append(os.path.join(git_repo_path, "utils"))
+
+import check_copies  # noqa: E402
+
+
+# This is the reference code that will be used in the tests.
+# If BertLMPredictionHead is changed in modeling_bert.py, this code needs to be manually updated.
+REFERENCE_CODE = """    def __init__(self, config):
+        super().__init__()
+        self.transform = BertPredictionHeadTransform(config)
+
+        # The output weights are the same as the input embeddings, but there is
+        # an output-only bias for each token.
+        self.decoder = nn.Linear(config.hidden_size, config.vocab_size, bias=False)
+
+        self.bias = nn.Parameter(torch.zeros(config.vocab_size))
+
+        # Need a link between the two variables so that the bias is correctly resized with `resize_token_embeddings`
+        self.decoder.bias = self.bias
+
+    def forward(self, hidden_states):
+        hidden_states = self.transform(hidden_states)
+        hidden_states = self.decoder(hidden_states)
+        return hidden_states
+"""
+
+
+class CopyCheckTester(unittest.TestCase):
+    def setUp(self):
+        self.transformer_dir = tempfile.mkdtemp()
+        check_copies.TRANSFORMER_PATH = self.transformer_dir
+        shutil.copy(
+            os.path.join(git_repo_path, "src/transformers/modeling_bert.py"),
+            os.path.join(self.transformer_dir, "modeling_bert.py"),
+        )
+
+    def tearDown(self):
+        check_copies.TRANSFORMER_PATH = "src/transformers"
+        shutil.rmtree(self.transformer_dir)
+
+    def check_copy_consistency(self, comment, class_name, class_code, overwrite_result=None):
+        code = comment + f"\nclass {class_name}(nn.Module):\n" + class_code
+        if overwrite_result is not None:
+            expected = comment + f"\nclass {class_name}(nn.Module):\n" + overwrite_result
+        fname = os.path.join(self.transformer_dir, "new_code.py")
+        with open(fname, "w") as f:
+            f.write(code)
+        if overwrite_result is None:
+            self.assertTrue(check_copies.is_copy_consistent(fname))
+        else:
+            check_copies.is_copy_consistent(f.name, overwrite=True)
+            with open(fname, "r") as f:
+                self.assertTrue(f.read(), expected)
+
+    def test_find_code_in_transformers(self):
+        code = check_copies.find_code_in_transformers("modeling_bert.BertLMPredictionHead")
+        self.assertEqual(code, REFERENCE_CODE)
+
+    def test_is_copy_consistent(self):
+        # Base copy consistency
+        self.check_copy_consistency(
+            "# Copied from transformers.modeling_bert.BertLMPredictionHead",
+            "BertLMPredictionHead",
+            REFERENCE_CODE + "\n",
+        )
+
+        # With no empty line at the end
+        self.check_copy_consistency(
+            "# Copied from transformers.modeling_bert.BertLMPredictionHead",
+            "BertLMPredictionHead",
+            REFERENCE_CODE,
+        )
+
+        # Copy consistency with rename
+        self.check_copy_consistency(
+            "# Copied from transformers.modeling_bert.BertLMPredictionHead with Bert->TestModel",
+            "TestModelLMPredictionHead",
+            re.sub("Bert", "TestModel", REFERENCE_CODE),
+        )
+
+        # Copy consistency with a really long name
+        long_class_name = "TestModelWithAReallyLongNameBecauseSomePeopleLikeThatForSomeReasonIReallyDontUnderstand"
+        self.check_copy_consistency(
+            f"# Copied from transformers.modeling_bert.BertLMPredictionHead with Bert->{long_class_name}",
+            f"{long_class_name}LMPredictionHead",
+            re.sub("Bert", long_class_name, REFERENCE_CODE),
+        )
+
+        # Copy consistency with overwrite
+        self.check_copy_consistency(
+            "# Copied from transformers.modeling_bert.BertLMPredictionHead with Bert->TestModel",
+            "TestModelLMPredictionHead",
+            REFERENCE_CODE,
+            overwrite_result=re.sub("Bert", "TestModel", REFERENCE_CODE),
+        )