Add deprecation warning for Pydantic v2 without --use-annotated

docs/cli-reference/typing-customization.md

@@ -2823,8 +2823,6 @@ syntax instead of default values. This also enables `--field-constraints`.
 
 **Related:** [`--field-constraints`](field-customization.md#field-constraints)
 
-**See also:** [Python Version Compatibility](../python-version-compatibility.md)
-
 !!! tip "Usage"
 
     ```bash

docs/llms-full.txt

@@ -14224,8 +14224,6 @@ syntax instead of default values. This also enables `--field-constraints`.
 
 **Related:** [`--field-constraints`](field-customization.md#field-constraints)
 
-**See also:** [Python Version Compatibility](../python-version-compatibility.md)
-
 !!! tip "Usage"
 
     ```bash

pyproject.toml

@@ -214,6 +214,7 @@ filterwarnings = [
   "error",
   "ignore:^.*Pydantic v1 runtime support is deprecated.*:DeprecationWarning",
   "ignore:^.*No --output-model-type specified.*:DeprecationWarning",
+  "ignore:^.*Pydantic v2 with --use-annotated is recommended.*:DeprecationWarning",
   "ignore:^.*`--validation` option is deprecated.*",
   "ignore:^.*--parent-scoped-naming is deprecated.*",
   "ignore:^.*Field name `name` is duplicated on Pet.*",

src/datamodel_code_generator/__main__.py

@@ -1209,6 +1209,22 @@ def main(args: Sequence[str] | None = None) -> Exit:  # noqa: PLR0911, PLR0912,
             stacklevel=1,
         )
 
+    if (
+        config.output_model_type in {DataModelType.PydanticV2BaseModel, DataModelType.PydanticV2Dataclass}
+        and not config.use_annotated
+        and namespace.use_annotated is None
+        and pyproject_config.get("use_annotated") is None
+    ):
+        warnings.warn(
+            "Pydantic v2 with --use-annotated is recommended for correct type annotations. "
+            "The current default (use_annotated=False) generates constrained types like "
+            "'conint(ge=1, le=365)' which are discouraged in Pydantic v2. "
+            "In a future version, --use-annotated will be enabled by default for Pydantic v2. "
+            "Please explicitly specify --use-annotated or --no-use-annotated.",
+            DeprecationWarning,
+            stacklevel=1,
+        )
+
     if not is_pydantic_v2():
         warnings.warn(
             "Pydantic v1 runtime support is deprecated and will be removed in a future version. "

src/datamodel_code_generator/arguments.py

@@ -520,8 +520,9 @@ def start_section(self, heading: str | None) -> None:
 )
 typing_options.add_argument(
     "--use-annotated",
-    help="Use typing.Annotated for Field(). Also, `--field-constraints` option will be enabled.",
-    action="store_true",
+    help="Use typing.Annotated for Field(). Also, `--field-constraints` option will be enabled. "
+    "Will become default for Pydantic v2 in a future version.",
+    action=BooleanOptionalAction,
     default=None,
 )
 typing_options.add_argument(

src/datamodel_code_generator/cli_options.py

@@ -179,6 +179,7 @@ class CLIOptionMeta:
         name="--use-generic-container-types", category=OptionCategory.TYPING
     ),
     "--use-annotated": CLIOptionMeta(name="--use-annotated", category=OptionCategory.TYPING),
+    "--no-use-annotated": CLIOptionMeta(name="--no-use-annotated", category=OptionCategory.TYPING),
     "--use-type-alias": CLIOptionMeta(name="--use-type-alias", category=OptionCategory.TYPING),
     "--use-root-model-type-alias": CLIOptionMeta(name="--use-root-model-type-alias", category=OptionCategory.TYPING),
     "--strict-types": CLIOptionMeta(name="--strict-types", category=OptionCategory.TYPING),

tests/main/test_main_general.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import warnings
 from argparse import ArgumentTypeError, Namespace
 from typing import TYPE_CHECKING
 
@@ -2240,3 +2241,53 @@ def test_custom_formatters_kwargs_invalid(output_file: Path, capsys: pytest.Capt
         capsys=capsys,
         expected_stderr_contains="Unable to load custom_formatters_kwargs mapping: must be a JSON string mapping",
     )
+
+
+def test_use_annotated_deprecation_warning_pydantic_v2(output_file: Path) -> None:
+    """Test that deprecation warning is emitted for Pydantic v2 without --use-annotated."""
+    with pytest.warns(DeprecationWarning, match=r"--use-annotated will be enabled by default for Pydantic v2"):
+        run_main_and_assert(
+            input_path=JSON_SCHEMA_DATA_PATH / "simple_string.json",
+            output_path=output_file,
+            input_file_type="jsonschema",
+            extra_args=["--output-model-type", "pydantic_v2.BaseModel"],
+        )
+
+
+def test_use_annotated_no_warning_with_flag(output_file: Path) -> None:
+    """Test that no warning is emitted when --use-annotated is explicitly set."""
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        run_main_and_assert(
+            input_path=JSON_SCHEMA_DATA_PATH / "simple_string.json",
+            output_path=output_file,
+            input_file_type="jsonschema",
+            extra_args=["--output-model-type", "pydantic_v2.BaseModel", "--use-annotated"],
+        )
+    assert not any("--use-annotated will be enabled" in str(warning.message) for warning in w)
+
+
+def test_use_annotated_no_warning_with_no_flag(output_file: Path) -> None:
+    """Test that no warning is emitted when --no-use-annotated is explicitly set."""
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        run_main_and_assert(
+            input_path=JSON_SCHEMA_DATA_PATH / "simple_string.json",
+            output_path=output_file,
+            input_file_type="jsonschema",
+            extra_args=["--output-model-type", "pydantic_v2.BaseModel", "--no-use-annotated"],
+        )
+    assert not any("--use-annotated will be enabled" in str(warning.message) for warning in w)
+
+
+def test_use_annotated_no_warning_pydantic_v1(output_file: Path) -> None:
+    """Test that use_annotated warning is not emitted for Pydantic v1."""
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        run_main_and_assert(
+            input_path=JSON_SCHEMA_DATA_PATH / "simple_string.json",
+            output_path=output_file,
+            input_file_type="jsonschema",
+            extra_args=["--output-model-type", "pydantic.BaseModel"],
+        )
+    assert not any("--use-annotated will be enabled" in str(warning.message) for warning in w)