🐛 Restore public QbField properties (#7480)

Restore the public `QbField` properties removed during the ORM
model-system update: `annotation`, `doc`, `is_attribute`,
and `is_subscriptable`.

These properties are part of the public `aiida.orm` API and can
be used by query helpers and plugin code. Add regression coverage
for the restored accessors.

Author: agoscinski

src/aiida/orm/fields.py

@@ -18,6 +18,7 @@
 from types import UnionType
 
 from aiida.common.lang import isidentifier
+from aiida.common.warnings import warn_deprecation
 
 __all__ = (
     'QbField',
@@ -92,11 +93,51 @@ def backend_key(self) -> str:
             return f'attributes.{self._backend_key}'
         return self._backend_key
 
+    @property
+    def doc(self) -> str:
+        """Return the field documentation string."""
+        warn_deprecation(
+            '`QbField.doc` is deprecated. Inspect the corresponding ORM model field description instead.',
+            version=3,
+            stacklevel=2,
+        )
+        return self._doc
+
     @property
     def dtype(self) -> t.Any | None:
         """Return the primitive root type."""
         return extract_root_type(self._dtype)
 
+    @property
+    def annotation(self) -> t.Any | None:
+        """Return the full type annotation."""
+        warn_deprecation(
+            '`QbField.annotation` is deprecated. Inspect the corresponding ORM model field annotation instead.',
+            version=3,
+            stacklevel=2,
+        )
+        return self._dtype
+
+    @property
+    def is_attribute(self) -> bool:
+        """Return whether the field is stored in the attributes namespace."""
+        warn_deprecation(
+            '`QbField.is_attribute` is deprecated. Inspect the corresponding ORM model field metadata instead.',
+            version=3,
+            stacklevel=2,
+        )
+        return self._is_attribute
+
+    @property
+    def is_subscriptable(self) -> bool:
+        """Return whether nested lookup through ``field['key']`` is supported."""
+        warn_deprecation(
+            '`QbField.is_subscriptable` is deprecated. Inspect the corresponding ORM model field metadata instead.',
+            version=3,
+            stacklevel=2,
+        )
+        return isinstance(self, QbDictField)
+
     def in_(self, value: t.Iterable[t.Any]):
         """Return a filter for only values in the list"""
         try:

tests/orm/test_fields.py

@@ -12,6 +12,7 @@
 from importlib_metadata import entry_points
 
 from aiida import orm
+from aiida.common.warnings import AiidaDeprecationWarning
 from aiida.orm.fields import add_field
 from aiida.orm.pydantic import OrmMetadataField
 from aiida.plugins import load_entry_point
@@ -60,10 +61,20 @@ class AttributesModel(orm.Data.AttributesModel):
     node = NewNode()
 
     assert 'key1' in node.fields
+    with pytest.warns(AiidaDeprecationWarning, match='QbField.doc'):
+        assert node.fields.key1.doc == ''
     assert node.fields.key1.dtype is str
+    with pytest.warns(AiidaDeprecationWarning, match='QbField.annotation'):
+        assert node.fields.key1.annotation is str
+    with pytest.warns(AiidaDeprecationWarning, match='QbField.is_attribute'):
+        assert node.fields.key1.is_attribute is True
+    with pytest.warns(AiidaDeprecationWarning, match='QbField.is_subscriptable'):
+        assert node.fields.key1.is_subscriptable is False
     assert isinstance(node.fields.key1, orm.fields.QbStrField)
     assert node.fields.key1.backend_key == 'attributes.key1'
     assert node.fields.key1 == node.fields.attributes.key1
+    with pytest.warns(AiidaDeprecationWarning, match='QbField.is_subscriptable'):
+        assert node.fields.attributes.is_subscriptable is True
 
 
 @pytest.mark.parametrize('key', ('|', 'some.field', '1key'))