Add warning when set "alias" in low level annontated field

pydantic/_internal/_fields.py

@@ -226,6 +226,7 @@ def collect_model_fields(  # noqa: C901
                     # Nothing stops us from just creating a new FieldInfo for this type hint, so we do this.
                     field_info = FieldInfo.from_annotation(ann_type)
         else:
+            _warning_if_annotate_have_low_level_alias(ann_type, ann_name)
             field_info = FieldInfo.from_annotated_attribute(ann_type, default)
             # attributes which are fields are removed from the class namespace:
             # 1. To match the behaviour of annotation-only fields
@@ -251,6 +252,21 @@ def collect_model_fields(  # noqa: C901
     return fields, class_vars
 
 
+def _warning_if_annotate_have_low_level_alias(ann_type: type[Any], ann_name: str):
+    from ..fields import FieldInfo
+
+    if hasattr(ann_type, '__args__'):
+        for anno_arg in ann_type.__args__:
+            if _typing_extra.is_annotated(anno_arg):
+                for anno_type_arg in _typing_extra.get_args(anno_arg):
+                    if isinstance(anno_type_arg, FieldInfo) and anno_type_arg.alias is not None:
+                        warnings.warn(
+                            f'Field "{ann_name}" has `alias` should be set at higher level to have affect',
+                            UserWarning,
+                        )
+                        break
+
+
 def _is_finalvar_with_default_val(type_: type[Any], val: Any) -> bool:
     from ..fields import FieldInfo
 

tests/test_annotated.py

@@ -1,5 +1,5 @@
 import sys
-from typing import Any, Generic, Iterator, List, Set, TypeVar
+from typing import Any, Generic, Iterator, List, Optional, Set, TypeVar
 
 import pytest
 from annotated_types import BaseMetadata, GroupedMetadata, Gt, Lt, Predicate
@@ -232,6 +232,17 @@ class _(BaseModel):
     calls.clear()
 
 
+def test_annotated_alias_at_low_level() -> None:
+    with pytest.warns(
+        UserWarning, match=r'Field "low_level_alias_field" has `alias` should be set at higher level to have affect'
+    ):
+
+        class Model(BaseModel):
+            low_level_alias_field: Optional[Annotated[int, Field(alias='field_alias')]] = None
+
+    assert Model(field_alias=1).low_level_alias_field is None
+
+
 def test_get_pydantic_core_schema_source_type() -> None:
     types: Set[Any] = set()