✅ Add regression test for unhashable Annotated in get_definitions

Add test that directly exercises get_definitions() with an Annotated
type containing unhashable metadata (simulating SQLModel extension
field-info objects). The test fails on main and passes with the fix.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

tests/test_openapi_unhashable_annotated.py

@@ -0,0 +1,35 @@
+from typing import Annotated
+
+from pydantic.fields import FieldInfo
+
+from fastapi._compat.v2 import ModelField, get_definitions
+
+
+class UnhashableMetadata:
+    """Simulates third-party field metadata (e.g. from SQLModel extensions)
+    that does not implement ``__hash__``."""
+
+    __hash__ = None  # type: ignore[assignment]
+
+
+def test_get_definitions_with_unhashable_annotation() -> None:
+    """``get_definitions()`` should not crash when a field annotation is an
+    ``Annotated`` type containing unhashable metadata.
+
+    Regression: the function used a set comprehension over
+    ``field_info.annotation`` values.  ``Annotated`` types that include
+    metadata with ``__hash__ = None`` (e.g. certain SQLModel / Pydantic
+    extension field-info objects) are themselves unhashable, causing
+    ``TypeError: unhashable type`` when building the set.
+    """
+    field = ModelField(
+        field_info=FieldInfo(annotation=Annotated[int, UnhashableMetadata()]),
+        name="test_field",
+        mode="validation",
+    )
+    # Should not raise TypeError
+    get_definitions(
+        fields=[field],
+        model_name_map={},
+        separate_input_output_schemas=True,
+    )