Harden logic for when typing_extensions doesn't alias TypeAliasType

python/src/typechat/_internal/ts_conversion/python_type_to_ts_nodes.py

@@ -2,6 +2,7 @@
 
 from collections import OrderedDict
 import inspect
+import sys
 import typing
 import typing_extensions
 from dataclasses import MISSING, Field, dataclass
@@ -79,6 +80,15 @@ class Dataclassish(Protocol):
 class TypeOfTypedDict(Protocol):
     __total__: bool
 
+if sys.version_info >= (3, 12) and typing.TypeAliasType is not typing_extensions.TypeAliasType:
+    # Sometimes typing_extensions aliases TypeAliasType,
+    # sometimes it's its own declaration.
+    def is_type_alias_type(py_type: object) -> TypeGuard[TypeAliasType]:
+        return isinstance(py_type, typing.TypeAliasType | typing_extensions.TypeAliasType)
+else:
+    def is_type_alias_type(py_type: object) -> TypeGuard[TypeAliasType]:
+        return isinstance(py_type, typing_extensions.TypeAliasType)
+
 
 def is_generic(py_type: object) -> TypeGuard[GenericAliasish]:
     return hasattr(py_type, "__origin__") and hasattr(py_type, "__args__")
@@ -88,9 +98,8 @@ def is_dataclass(py_type: object) -> TypeGuard[Dataclassish]:
 
 TypeReferenceTarget: TypeAlias = type | TypeAliasType | TypeVar | GenericAliasish
 
-
 def is_python_type_or_alias(origin: object) -> TypeGuard[type | TypeAliasType]:
-    return isinstance(origin, TypeAliasType | type)
+    return isinstance(origin, type) or is_type_alias_type(origin)
 
 
 _KNOWN_GENERIC_SPECIAL_FORMS: frozenset[Any] = frozenset(
@@ -393,7 +402,7 @@ def declare_type(py_type: object):
             reserve_name(py_type)
 
             return InterfaceDeclarationNode(py_type.__name__, None, "", None, [])
-        if isinstance(py_type, TypeAliasType):
+        if is_type_alias_type(py_type):
             type_params = [TypeParameterDeclarationNode(type_param.__name__) for type_param in py_type.__type_params__]
 
             reserve_name(py_type)

python/tests/__py3.12+_snapshots__/test_generic_alias_3/test_generic_alias3.schema.d.ts

@@ -0,0 +1,13 @@
+// Entry point is: 'FirstOrSecond'
+
+type FirstOrSecond<T> = First<T> | Second<T>
+
+interface Second<T> {
+    kind: "second";
+    second_attr: T;
+}
+
+interface First<T> {
+    kind: "first";
+    first_attr: T;
+}

python/tests/__py3.12+_snapshots__/test_type_alias_syntax/test_type_alias_union1.schema.d.ts

@@ -0,0 +1,3 @@
+// Entry point is: 'StrOrInt'
+
+type StrOrInt = string | number

python/tests/__snapshots__/test_generic_alias_2/test_generic_alias2.schema.d.ts

@@ -0,0 +1,17 @@
+// Entry point is: 'Nested'
+
+interface Nested {
+    item: FirstOrSecond<string>;
+}
+
+type FirstOrSecond<T> = First<T> | Second<T>
+
+interface Second<T> {
+    kind: "second";
+    second_attr: T;
+}
+
+interface First<T> {
+    kind: "first";
+    first_attr: T;
+}

python/tests/test_generic_alias_1.py

@@ -5,7 +5,6 @@
 
 T = TypeVar("T", covariant=True)
 
-
 class First(Generic[T], TypedDict):
     kind: Literal["first"]
     first_attr: T

python/tests/test_generic_alias_2.py

@@ -22,7 +22,5 @@ class Nested(TypedDict):
     item: FirstOrSecond[str]
 
 
-
-def test_generic_alias1(snapshot: Any):
+def test_generic_alias2(snapshot: Any):
     assert(python_type_to_typescript_schema(Nested) == snapshot(extension_class=TypeScriptSchemaSnapshotExtension))
-

python/tests/test_generic_alias_3.py

@@ -0,0 +1,20 @@
+from typing import Any
+from .utilities import check_snapshot_for_module_string_if_3_12_plus
+
+module_str = """
+from typing import Literal, TypedDict
+class First[T](TypedDict):
+    kind: Literal["first"]
+    first_attr: T
+
+
+class Second[T](TypedDict):
+    kind: Literal["second"]
+    second_attr: T
+
+
+type FirstOrSecond[T] = First[T] | Second[T]
+"""
+
+def test_generic_alias3(snapshot: Any):
+    check_snapshot_for_module_string_if_3_12_plus(snapshot, input_type_str="FirstOrSecond", module_str=module_str)

python/tests/test_generic_alias_4.py

@@ -0,0 +1,23 @@
+from typing import Any
+from .utilities import check_snapshot_for_module_string_if_3_12_plus
+
+module_str = """
+from typing import Literal, TypedDict
+class First[T](TypedDict):
+    kind: Literal["first"]
+    first_attr: T
+
+
+class Second[T](TypedDict):
+    kind: Literal["second"]
+    second_attr: T
+
+
+type FirstOrSecond[T] = First[T] | Second[T]
+
+class Nested(TypedDict):
+    item: FirstOrSecond[str]
+"""
+
+def test_generic_alias4(snapshot: Any):
+    check_snapshot_for_module_string_if_3_12_plus(snapshot, input_type_str="Nested", module_str=module_str)

python/tests/test_type_alias_syntax.py

@@ -0,0 +1,7 @@
+from typing import Any
+from .utilities import check_snapshot_for_module_string_if_3_12_plus
+
+module_str = "type StrOrInt = str | int"
+
+def test_type_alias_union1(snapshot: Any):
+    check_snapshot_for_module_string_if_3_12_plus(snapshot, "StrOrInt", module_str)

python/tests/utilities.py

@@ -1,13 +1,14 @@
 from pathlib import Path
 import sys
+import types
 
 from typing_extensions import Any, override
 import pytest
 
 from syrupy.extensions.single_file import SingleFileSnapshotExtension, WriteMode
 from syrupy.location import PyTestLocation
 
-from typechat._internal.ts_conversion import TypeScriptSchemaConversionResult
+from typechat._internal.ts_conversion import TypeScriptSchemaConversionResult, python_type_to_typescript_schema
 
 class TypeScriptSchemaSnapshotExtension(SingleFileSnapshotExtension):
     _write_mode = WriteMode.TEXT
@@ -41,6 +42,19 @@ def dirname(cls, *, test_location: PyTestLocation) -> str:
         )
         return str(result)
 
+class PyVersioned3_12_PlusSnapshotExtension(PyVersionedTypeScriptSchemaSnapshotExtension):
+    py_ver_dir: str = f"__py3.12+_snapshots__"
+
+def check_snapshot_for_module_string_if_3_12_plus(snapshot: Any, input_type_str: str, module_str: str):
+    if sys.version_info < (3, 12):
+        pytest.skip("requires python 3.12 or higher")
+
+    module = types.ModuleType("test_module")
+    exec(module_str, module.__dict__)
+    type_obj = eval(input_type_str, globals(), module.__dict__)
+
+    assert(python_type_to_typescript_schema(type_obj) == snapshot(extension_class=PyVersioned3_12_PlusSnapshotExtension))
+
 @pytest.fixture
 def snapshot_schema(snapshot: Any):
     return snapshot.with_defaults(extension_class=TypeScriptSchemaSnapshotExtension)