Improve handling of generic types in json-schema

apischema/json_schema/refs.py

@@ -27,7 +27,7 @@
 
 
 def _default_ref(cls: AnyType) -> Ref:
-    if (
+    if not hasattr(cls, "__parameters__") and (
         is_dataclass(cls)
         or hasattr(cls, "__supertype__")
         or isinstance(cls, _TypedDictMeta)
@@ -59,13 +59,21 @@ def __post_init__(self):
             raise ValueError("Empty schema ref not allowed")
 
     def check_type(self, cls: AnyType):
-        """Check if the given type can have a ref
-
-        NewType of non-builtin types cannot have a ref because their serialization
-        could be customized, but the NewType ref would then erase this customization
-        in the schema"""
         if hasattr(cls, "__supertype__") and not is_builtin(cls):
+            # NewType of non-builtin types cannot have a ref because their serialization
+            # could be customized, but the NewType ref would then erase this
+            # customization in the schema.
             raise TypeError("NewType of non-builtin type can not have a ref")
+        if hasattr(cls, "__parameters__") and (
+            not hasattr(cls, "__origin__")
+            or any(
+                isinstance(arg, TypeVar)  # type: ignore
+                for arg in getattr(cls, "__args__", ())
+            )
+        ):
+            raise TypeError("Unspecialized generic types cannot have a ref")
+        if hasattr(cls, "__origin__") and self.ref is ...:
+            raise TypeError(f"Generic alias {cls} cannot have ... ref")
 
     def __call__(self, cls: T) -> T:
         self.check_type(cls)

tests/test_refs.py

@@ -1,7 +1,11 @@
 from dataclasses import dataclass
-from typing import List, Optional
+from typing import Generic, List, Optional, TypeVar
+
+from _pytest.python_api import raises
+from pytest import mark
 
 from apischema import schema_ref
+from apischema.json_schema import deserialization_schema
 from apischema.json_schema.generation.builder import DeserializationSchemaBuilder
 from apischema.typing import Annotated
 
@@ -42,3 +46,52 @@ def test_find_refs():
         "Bs2": (Annotated[List[B], schema_ref("Bs2")], 1),
         "Recursive": (Recursive, 2),
     }
+
+
+T = TypeVar("T")
+U = TypeVar("U")
+
+
+@dataclass
+class DataGeneric(Generic[T]):
+    a: T
+
+
+schema_ref("StrData")(DataGeneric[str])
+
+
+@mark.parametrize("cls", [DataGeneric, DataGeneric[U], DataGeneric[int]])
+def test_generic_ref_error(cls):
+    with raises(TypeError):
+        schema_ref(...)(cls)
+
+
+def test_generic_schema():
+    schema_ref("StrData")(DataGeneric[str])
+    print()
+    assert deserialization_schema(DataGeneric, all_refs=True) == {
+        "$schema": "http://json-schema.org/draft/2019-09/schema#",
+        "type": "object",
+        "properties": {"a": {}},
+        "required": ["a"],
+        "additionalProperties": False,
+    }
+    assert deserialization_schema(DataGeneric[int], all_refs=True) == {
+        "$schema": "http://json-schema.org/draft/2019-09/schema#",
+        "type": "object",
+        "properties": {"a": {"type": "integer"}},
+        "required": ["a"],
+        "additionalProperties": False,
+    }
+    assert deserialization_schema(DataGeneric[str], all_refs=True) == {
+        "$schema": "http://json-schema.org/draft/2019-09/schema#",
+        "$ref": "#/$defs/StrData",
+        "$defs": {
+            "StrData": {
+                "type": "object",
+                "properties": {"a": {"type": "string"}},
+                "required": ["a"],
+                "additionalProperties": False,
+            }
+        },
+    }