Use Literal type for nr_feature_tokens

requirements.txt

@@ -20,6 +20,7 @@ pytokenizations
 setuptools
 packaging
 importlib_metadata>=0.20; python_version < "3.8"
+typing_extensions>=3.7.4; python_version < "3.8"
 # Development dependencies
 cython>=0.25
 pytest>=4.6.5

setup.cfg

@@ -57,6 +57,7 @@ install_requires =
     setuptools
     packaging
     importlib_metadata>=0.20; python_version < "3.8"
+    typing_extensions>=3.7.4; python_version < "3.8"
 
 [options.entry_points]
 console_scripts =

spacy/compat.py

@@ -22,6 +22,11 @@ try:
 except ImportError:
     cupy = None
 
+try:  # Python 3.8+
+    from typing import Literal
+except ImportError:
+    from typing_extensions import Literal  # noqa: F401
+
 from thinc.api import Optimizer  # noqa: F401
 
 pickle = pickle

spacy/ml/models/parser.py

@@ -2,6 +2,7 @@ from typing import Optional, List
 from thinc.api import Model, chain, list2array, Linear, zero_init, use_ops
 from thinc.types import Floats2d
 
+from ...compat import Literal
 from ...util import registry
 from .._precomputable_affine import PrecomputableAffine
 from ..tb_framework import TransitionModel
@@ -11,7 +12,7 @@ from ...tokens import Doc
 @registry.architectures.register("spacy.TransitionBasedParser.v1")
 def build_tb_parser_model(
     tok2vec: Model[List[Doc], List[Floats2d]],
-    nr_feature_tokens: int,
+    nr_feature_tokens: Literal[3, 6, 8, 13],
     hidden_width: int,
     maxout_pieces: int,
     use_upper: bool = True,

spacy/tests/serialize/test_serialize_config.py

@@ -67,7 +67,7 @@ width = ${components.tok2vec.model.width}
 parser_config_string = """
 [model]
 @architectures = "spacy.TransitionBasedParser.v1"
-nr_feature_tokens = 99
+nr_feature_tokens = 3
 hidden_width = 66
 maxout_pieces = 2
 
@@ -95,7 +95,7 @@ def my_parser():
         MaxoutWindowEncoder(width=321, window_size=3, maxout_pieces=4, depth=2),
     )
     parser = build_tb_parser_model(
-        tok2vec=tok2vec, nr_feature_tokens=7, hidden_width=65, maxout_pieces=5
+        tok2vec=tok2vec, nr_feature_tokens=8, hidden_width=65, maxout_pieces=5
     )
     return parser
 
@@ -340,3 +340,13 @@ def test_config_auto_fill_extra_fields():
     assert "extra" not in nlp.config["training"]
     # Make sure the config generated is valid
     load_model_from_config(nlp.config)
+
+
+def test_config_validate_literal():
+    nlp = English()
+    config = Config().from_str(parser_config_string)
+    config["model"]["nr_feature_tokens"] = 666
+    with pytest.raises(ConfigValidationError):
+        nlp.add_pipe("parser", config=config)
+    config["model"]["nr_feature_tokens"] = 13
+    nlp.add_pipe("parser", config=config)