fix: Deterministic alias selection when using validate_by_name (#707)

Author: chbndrhnns

pydantic_settings/main.py

@@ -466,7 +466,9 @@ def _settings_restore_init_kwarg_names(
             for field_name, field_info in settings_cls.model_fields.items():
                 alias_names, *_ = _get_alias_names(field_name, field_info)
                 matchable_names = set(alias_names)
-                include_name = settings_cls.model_config.get('populate_by_name', False)
+                include_name = settings_cls.model_config.get(
+                    'populate_by_name', False
+                ) or settings_cls.model_config.get('validate_by_name', False)
                 if include_name:
                     matchable_names.add(field_name)
                 init_kwarg_name = init_kwarg_names & matchable_names

pydantic_settings/sources/base.py

@@ -267,7 +267,9 @@ def __init__(
             # When populate_by_name is True, allow using the field name as an input key,
             # but normalize to the preferred alias to keep keys consistent across sources.
             matchable_names = set(alias_names)
-            include_name = settings_cls.model_config.get('populate_by_name', False)
+            include_name = settings_cls.model_config.get('populate_by_name', False) or settings_cls.model_config.get(
+                'validate_by_name', False
+            )
             if include_name:
                 matchable_names.add(field_name)
             init_kwarg_name = init_kwarg_names & matchable_names
@@ -369,7 +371,7 @@ def _extract_field_info(self, field: FieldInfo, field_name: str) -> list[tuple[s
             else:  # string validation alias
                 field_info.append((v_alias, self._apply_case_sensitive(v_alias), False))
 
-        if not v_alias or self.config.get('populate_by_name', False):
+        if not v_alias or self.config.get('populate_by_name', False) or self.config.get('validate_by_name', False):
             annotation = field.annotation
             if typing_objects.is_typealiastype(annotation) or typing_objects.is_typealiastype(get_origin(annotation)):
                 annotation = _strip_annotated(annotation.__value__)  # type: ignore[union-attr]
@@ -489,7 +491,13 @@ def _get_resolved_field_value(self, field: FieldInfo, field_name: str) -> tuple[
             A tuple that contains the value, preferred key and a flag to determine whether value is complex.
         """
         field_value, field_key, value_is_complex = self.get_field_value(field, field_name)
-        if not (value_is_complex or (self.config.get('populate_by_name', False) and (field_key == field_name))):
+        if not (
+            value_is_complex
+            or (
+                (self.config.get('populate_by_name', False) or self.config.get('validate_by_name', False))
+                and (field_key == field_name)
+            )
+        ):
             field_infos = self._extract_field_info(field, field_name)
             preferred_key, *_ = field_infos[0]
             return field_value, preferred_key, value_is_complex