docs: Improve --use-type-alias help text documentation

[staging-devin-ai-integration]

Summary

Updates the CLI help text for the --use-type-alias flag to provide clearer documentation about its functionality and limitations.

Changes

The help text for --use-type-alias has been updated from:

Use TypeAlias instead of root models (experimental)

To:

Generate Python type aliases instead of RootModel classes. Uses 'type' statement for Python 3.12+, TypeAliasType for Pydantic v2 on 3.10-3.11, and TypeAlias annotation for Pydantic v1. Note: Type aliases don't support model_config or field-specific metadata like default/alias.

Version Matrix Documentation

The updated help text now documents the following version matrix:

Pydantic Version	Python Version	Output Format
Pydantic v2	Python 3.12+	type Name = type (native type statement)
Pydantic v2	Python 3.10-3.11	Name = TypeAliasType("Name", type)
Pydantic v1	Python 3.10+	Name: TypeAlias = type

Limitations Documented

The help text now notes that type aliases don't support:

• model_config configuration
• Field-specific metadata like default, alias, etc.

Related Issues

• Use annotated type instead of the RootModel koxudaxi/datamodel-code-generator#2427: RootModel doesn't work well with validate_call
• Generate Annotated types instead of root types for string constraints koxudaxi/datamodel-code-generator#2018: Users want simpler Annotated types instead of RootModel wrappers
• Add an option to generate TypeAlias for literals when using the --enum-field-as-literal koxudaxi/datamodel-code-generator#1285: No way to get reusable TypeAlias definitions with --enum-field-as-literal
• TypeAlias does not work for python versions <3.10 koxudaxi/datamodel-code-generator#1848: The existing TypeAlias output doesn't account for Python version differences

Testing

All existing type_alias tests pass:

tests/main/jsonschema/test_main_jsonschema.py::test_main_type_alias_forward_ref_keep_model_order PASSED
tests/main/jsonschema/test_main_jsonschema.py::test_main_type_alias_cycle_keep_model_order PASSED
tests/main/jsonschema/test_main_jsonschema.py::test_main_jsonschema_type_alias PASSED
tests/main/jsonschema/test_main_jsonschema.py::test_main_jsonschema_type_alias_py312 PASSED
tests/main/jsonschema/test_main_jsonschema.py::test_main_jsonschema_type_alias_with_field_description PASSED
tests/main/jsonschema/test_main_jsonschema.py::test_main_jsonschema_type_alias_with_field_description_py312 PASSED
tests/main/jsonschema/test_main_jsonschema.py::test_main_jsonschema_type_alias_with_circular_ref_to_class_msgspec PASSED
tests/main/jsonschema/test_main_jsonschema.py::test_main_use_root_model_type_alias PASSED

[staging-devin-ai-integration]

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