Add missing _add_value_alias_ method for Python 3.13 enum

[tjdcs]

Fixes #14408

Summary

• Add missing _add_value_alias_ method to Enum class for Python 3.13
• Add comprehensive test cases for the MultiValueEnum pattern

Fixes #14408 by resolving the type checker error when using _add_value_alias_ method in Python 3.13 enum classes.

Changes Made

• Added _add_value_alias_(self, value: Any) -> None method to Enum class in stdlib/enum.pyi
• Added proper Python 3.13 version guard (if sys.version_info >= (3, 13):)
• Added comprehensive test cases in stdlib/@tests/test_cases/check_enum.py including:
  • MultiValueEnum pattern from Python documentation
  • Type inference tests for primary and alias values
  • Literal type verification

Test Plan

• Verify Pyright recognizes the method without errors (0 errors, 0 warnings)
• Verify mypy recognizes the method without errors (Success: no issues found)
• Test runtime functionality with Python 3.13 (✅ Works correctly)
• Ensure no regressions in existing enum functionality (✅ All tests pass)
• Test cases pass with both type checkers (✅ Pyright and mypy both succeed)

Example Usage

from enum import Enum

class MultiValueEnum(Enum):
    def __new__(cls, value, *values):
        self = object.__new__(cls)
        self._value_ = value
        for v in values:
            self._add_value_alias_(v)  # No longer causes type error
        return self

class DType(MultiValueEnum):
    float32 = 'f', 8
    double64 = 'd', 9

# Both work correctly
print(DType('f'))  # <DType.float32: 'f'>
print(DType(8))    # <DType.float32: 'f'>

🤖 Generated with Claude Code

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[srittau]

Thanks, remarks below. We should also add overridden variants of this method to StrEnum and IntEnum, similar to what we do for other attributes/methods where value is used.

Also, for future reference: Please don't use AI PR summaries. Those use a lot of words for something very simple, making it considerably harder to understand the issue and PR. In this case, a simple link back to the original issued would have sufficed.

[srittau]

These tests don't seem to test anything relevant – at least not as it relates to type annotations. We generally don't run our test cases, we just type check them, so any logic is meaningless. This is also seems to test something called a MultiValueEnum, which isn't a concept in Python's stdlib.

[srittau]

We nowadays require explanatory comments for all non-obvious Anys. In this case, maybe the following comment makes sense?

Suggested change

	def _add_value_alias_(self, value: Any) -> None: ...
	# value must have the same type as other enum members
	def _add_value_alias_(self, value: Any) -> None: ...

[donBarbos]

I would like to note that the _add_alias_ method was added in the same version, and it would be possible to add them together

[tjdcs]

Thank you for your comments. Give me a day or two to address them and correct this PR. I will add the requisite comments, remove the irrelevant tests, and check the additional special enum types.

Also, my apologies for the verbose PR summary. I was really just letting Claude run rampant and see what he did / what he came up with. I'll keep that in mind for the future.