Add test for case where parser overwrite annotations (#9406)

* Add test for case where parser overwrite annotations

* Move test to its own file

Also add note about how other tokens modify results.

* Fix xfail decorator

spacy/tests/regression/test_issue7716.py

@@ -0,0 +1,54 @@
+import pytest
+from thinc.api import Adam
+from spacy.attrs import NORM
+from spacy.vocab import Vocab
+from spacy import registry
+from spacy.training import Example
+from spacy.pipeline.dep_parser import DEFAULT_PARSER_MODEL
+from spacy.tokens import Doc
+from spacy.pipeline import DependencyParser
+
+
+@pytest.fixture
+def vocab():
+    return Vocab(lex_attr_getters={NORM: lambda s: s})
+
+
+def _parser_example(parser):
+    doc = Doc(parser.vocab, words=["a", "b", "c", "d"])
+    gold = {"heads": [1, 1, 3, 3], "deps": ["right", "ROOT", "left", "ROOT"]}
+    return Example.from_dict(doc, gold)
+
+
+@pytest.fixture
+def parser(vocab):
+    vocab.strings.add("ROOT")
+    cfg = {"model": DEFAULT_PARSER_MODEL}
+    model = registry.resolve(cfg, validate=True)["model"]
+    parser = DependencyParser(vocab, model)
+    parser.cfg["token_vector_width"] = 4
+    parser.cfg["hidden_width"] = 32
+    # parser.add_label('right')
+    parser.add_label("left")
+    parser.initialize(lambda: [_parser_example(parser)])
+    sgd = Adam(0.001)
+
+    for i in range(10):
+        losses = {}
+        doc = Doc(vocab, words=["a", "b", "c", "d"])
+        example = Example.from_dict(
+            doc, {"heads": [1, 1, 3, 3], "deps": ["left", "ROOT", "left", "ROOT"]}
+        )
+        parser.update([example], sgd=sgd, losses=losses)
+    return parser
+
+
+@pytest.mark.xfail(reason="Not fixed yet")
+def test_partial_annotation(parser):
+    doc = Doc(parser.vocab, words=["a", "b", "c", "d"])
+    doc[2].is_sent_start = False
+    # Note that if the following line is used, then doc[2].is_sent_start == False
+    # doc[3].is_sent_start = False
+
+    doc = parser(doc)
+    assert doc[2].is_sent_start == False